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Everything About Dengue Fever

Mosquito bite

(Para leer este artículo en español, haga clic aquí.)

“Spiking fever, searing muscle and joint pain, blood seeping through the skin, shock and possibly death—the severest form of dengue fever can inflict unspeakable misery. Once rare, dengue fever now threatens more than 2.5 billion people.” (1)

“Dengue is the most rapidly spreading mosquito-borne viral disease in the world. In the last 50 years, incidence has increased 30-fold with increasing geographic expansion to new countries and, in the present decade, from urban to rural settings…” (2)

History of Dengue Fever

People’s stories from hundreds and thousands of years ago tell the origins of ka-dinga pepo: the “disease of the devil” (in Swahili), a.k.a. Dengue Virus. Roughly 2000 years ago, one species of mosquito (Aedes aegypti) found new hosts. Those hosts lived in cities and villages along the Nile, and they recorded their experiences for us to read today. They told tales of a terrible illness that started with a fever and often a rash and easy-bruising. It caused unbelievable pain in the bones and joints, with a special pain emanating from behind the eyes. In its worst forms, the suffering included bleeding from the eyes and oozing blood from the pores. Some recovered, some died. (1)

These entrepreneurial mosquitoes spread across the tropical and sub-tropical world, eventually stowing away on ships with slave traders and rum-runners, and making their way to 17th century Boston and Philadelphia. By 1780, the famed Dr. Benjamin Rush (a signer of the Declaration of Independence) reported treating an outbreak of “Bone Break Fever” among Philadelphia residents, and the name stuck.(1)

Dengue Virus (DV) infections continued to plague much of the Tropical New World until hemisphere-wide mosquito eradication efforts in the 1950’s and 1960’s nearly exterminated it in the Western Hemisphere. 1945 marked the last Dengue epidemic in the United States. Unfortunately, Cuba did not eradicate their Aedes aegypti mosquitoes, although Castro maintained an official public façade that Cuba too should be certified as a Dengue-free nation. Cuba’s living population of Aedes aegypti mosquitoes and their accompanying Dengue Virus apparently provided an ongoing reservoir of Dengue Virus for re-infecting all the Caribbean and Central American and South American nations. (2,3)

Dengue in Mexico

Dengue virus re-appeared in Mexico in 1968 and has spread across almost of Mexico as Aedes aegypti mosquitos moved inland from the Gulf Coastal regions. Since that time, city-loving Aedes aegypti mosquitos and the Dengue Virus have basically been endemic to the Yucatan Peninsula, with confirmed Dengue Virus cases peaking and increasing the past 3 years in Yucatan State. (3)

This year, the Federal Government of Mexico has announced that overall cases of the milder, classic form of Dengue have fallen slightly in Mexico since 2009. "But the more serious hemorrhagic form has spiked to about 1,900 cases this year, compared with about 1,430 in the same period of 2009. Only 16 people have died this year from the hemorrhagic form, but the seriousness of the disease makes it a concern." For the first time in 64 years, there is evidence of Dengue in the United States as well (in Key West, Florida).

Dengue Fact Sheet

  • Dengue infections in Merida and the Yucatan beach areas are 4 times higher this Spring 2010 than they were a year ago.
  • Current rate may result in over 120,000 new Dengue Virus infections in Yucatan in 2010.
  • The recent rates of Dengue Hemorraghic Fever as a percentage (%) of total confirmed Dengue virus infections have exceeded 50% across most of Mexico,  which means that more than 50% of the confirmed Dengue virus cases proceeded to Dengue Hemorraghic Fever symptoms.
  • 2.5 billion people – two fifths of the world’s population – are now at risk from Dengue.
  • 50 million new Dengue Virus infections occur annually.
  • Dengue Virus is transmitted only through being bitten by Dengue-infected female Aedes Aegypti (silent) mosquitoes in the Americas.
  • Infection by 1 of 4 Dengue strains gives protection against only that strain for 4 months.
  • Infection by the other 3 strains are possible during the meantime, and re-infection by the first strain is possible after 4 months.
  • There is no such thing as "Dengue H".
  • All four Dengue Virus strains (DV-1, … , DV-4) are circulating in and endemic to the Yucatan Peninsula.
  • Prior Dengue infections seem to almost universally interfere with your subsequent immune responses to new Dengue infections, with each new infection producing more and more severe symptoms, increasing the likelyhood of the possibly fatal Dengue Hemorrhagic Fever (DHF) & Dengue Shock Syndrome (DSS).
  • Dengue infections take several forms. Infections can present no symptoms, mild symptoms like just a rash, flu-like symptoms, distinctive pain behind the eyes, high fevers (104ºF or 40ºC), and sometimes fatal Dengue Hemorrhagic Fever with bleeding from the eyes, under the skin, and into the Gastro-Intestinal Tract.
  • There is often a 3-week delay between the mosquito bite and onset of Dengue symptoms. There are anecdotal reports of as little as 4 days between being bitten and the onset of symptoms.
  • The key days for getting Dengue testing are DAYS 4 – 6 after onset of fever/symptoms.

Different Types of Dengue Infections

It is important to understand the different types of infections so that you will know how to treat yourself and your loved ones.

  • Primary Dengue Infections (First-Time Offenders): The commonly-used lab tests do not detect Dengue until Day 4 – Day 6 after the onset of symptoms. Waiting to get a tested during Days 4 – 6 will not change either your symptoms or medical treatments, unless your symptoms progress to DHF or DSS around Day 6.
  • Secondary Dengue Infections (Infected people who have already had a prior Dengue Infection): The commonly-used lab tests do not detect Dengue until Day 10 after onset of symptoms, because prior Dengue infections heavily interfere with the patient’s immune response to the new infection.

How Do I Know if I Have Dengue?

Yucatan has only two labs that do Dengue testing: a Departmento de Salud lab and one at Universidad Autonoma de Yucatan (UADY). Turn-around times (TATs) for Dengue test results CAN be 1 day. Free Physician Evaluations and Free Testing are available at UADY’s  Centro de Investigaciones "Hideyo Noguchi" research laboratory, across Calle 59 from the Merida Centennario Zoo, on the NE corner of  Avenida Itzaes and Calle 59.

Park across the street at the park (Parque de la Paz) in front of the old jail/penitentiary.  Walk into the building that is across from the Park on the northeast corner of Itzaes and Calle 59. Walk up to the front desk as you enter the Research Center, and explain that you need to be checked for Dengue.

"Ayudame, por favor." (Please help me)
"Yo penso que yo tener una infeccion de Dengue Virus."
(I think I am infected with Dengue Virus)
"Aqui se realizo pruebas de diagnostico de Dengue."
(I understand you can test for Dengue here)

 

The Mosquitos that Carry Dengue and How to Get Rid of ThemTeaspoon of Water

The Dengue carrying mosquitoes Aedes aegypti (A.ae.) mosquitoes need only a teaspoon of water that doesn’t evaporate for one week to convert eggs to free-flying adults at Yucatecan temperatures. With the kind of rain that this area has been experiencing over the past month, imagine all the teaspoons of water that might be lurking in your garden and your yard.

They (A. ae.) prefer clean water (or rain-water) residues, like those found in tinacos, flower pots, rubbish piles, old tires, old pipes, junk, rain water in unattended swimming pools, sink & floor drains, etc. The best methods for reducing Dengue risks are to kill and exclude mosquitoes from any areas where people live.

Other prevention ideas? Fountain in Merida Yucatan

  • When you are outside, wear long pants and socks or use a repellent.
  • Put screens on your windows and doors to keep mosquitoes outside, especially at night.
  • Seal or invert containers that might be outside in the rain, or which have water in them
  • Put mosquito larvae-eating fish like gambusia or guppies into ponds or fountains
  • Treat your fountains with chlorine to kill larvae at least weekly, plus use a copper algaecide to protect the chlorine. Since chlorine levels rapidly drop to ineffective levels when algae grows, especially after a rain, adding copper sulfate as an algaecide protects the chlorine.
  • Typical larvicides (like Abate (Temephos) or copper salts : a.k.a. Paris Green) kill larvae for a long period of time, unless you drain the water. The old time larvicide Paris Green is a mix of Copper Arsenate and Copper Acetate, called cardenillo, verdigris, or aerugo in Spanish. It should be used as a dry powder at 1% – 3% levels that floats on the surface of the water. Various formulations of Temephos are sold under the trade-name “Abate” and are reported to work for at least 1 month and up to a year, depending on the application.
  • Eliminate even small amounts of water that stand for a week or more

lab ratsThe adult A.ae. mosquitoes live roughly 1 month “in the wild” (normal conditions). Under better conditions, (like a nice laboratory with 3 hot meals and a cot), they can live for 6 months. Once an A.ae. adult mosquito gets Dengue Virus, they can transmit it for the rest of their little lives: 1 month – 6 months.

More About Larvicides

Larvicides are generally considered to be more effective at controlling mosquito populations than spraying to kill adult mosquitoes. Larvicides are also typically less toxic to humans than adult mosquito sprays, since they are usually applied to water that humans do not drink.

Maintaining sufficient free chlorine in a swimming pool or fountain also acts as a larvicide. When free chlorine levels fall in a pool or fountain, then mosquito larvae thrive. Copper Sulfate is one compound commonly used as an algaecide in swimming pools, because Copper Sulfate is nearly permanent (works until you drain the pool), and it protects the free chlorine from being chewed-up (consumed) by algae blooms that come after a rainfall(s). Rainfalls inject our swimming pools and fountains with algae-spore-laden dust, and the rainfall here is also generally basic (pH up to 9). Both the algae injection and pH increase reduces the amount of free chlorine very rapidly, reducing disinfecting power and reducing chlorine’s effect as a larvicide. (Now you know why your pool turns green faster after a rainfall!)

Since Aedes aegypti mosquitoes need one week for eggs to hatch and larvae to mature into free flying adults, if you maintain sufficient chlorine levels at least once a week, and suppress algae with an algaecide, then you effectively interrupt the mosquito’s breeding cycle by killing the larvae. Copper Sulfate (Tri-Hydrate) is available locally at places like Home Depot or the Baroso pool supply stores, and it only takes 34 grams (roughly 5 level tablespoons) of the pretty blue Copper Sulfate Tri-Hydrate salt to treat 50,000 liters of water (13,200 gal.).

A different form or type of larvicide, Paris Green (also using copper salts), is used for treating old tires, unused swimming pools, and other unused water features. In Spanish Paris Green is called cardenillo, verdigris, and aerugo. Paris Green is a toxic double salt of copper arsenate and copper acetate that floats on top of the water, which is why it is only typically used in old tires and other sources of unused standing water. It may also be worth considering using a synthetic organic pesticide larvicide like Abate (Temephos) .

Abate can be applied in various forms and concentrations, lasts a long time, and seems appropriate as a larvicide for non-drinking water supplies, based on USEPA reports. The USEPA reports that:

“Temephos, applied according to the label for mosquito control, does not pose unreasonable risks to human health.” (5)
“Temephos is not expected to have a direct impact on terrestrial animals. Risk quotients for freshwater fish only slightly exceed levels of concern; no acute toxicity data are available for marine fish species. Field monitoring data indicate little impact on birds. Aquatic invertebrates, particularly Daphnia magna, are extremely sensitive to temephos.” (5)

One final option of larvicides for mosquito control are natural pesticides that utilize bacteria spores to kill the larvae. Bacillus thuringiensis israelensis (called Bti for short) is a naturally occurring soil bacteria spore used to control mosquito larvae by releasing toxins into the mosquito’s gut, causing the larvae to stop eating and die. Since the larvae must eat the spores, Bti is only effective against actively feeding larvae, and does not affect mosquito pupae or adults. Because of its mosquito-larvae-only specific way of action, the USEPA reports that microbial larvicides (including Bti) are “essentially non-toxic to humans”, and that “microbial larvicides do not pose risks to wildlife, nontarget species, or the environment, when used according to label directions.“ (citation here)

There is one significant drawback to using Bti; it is reported to last only seven days in some applications. We hear Bti might be available here in Merida, but we cannot tell you where… yet!

What About the Neighbors?

If you think your neighbors are raising and herding mosquitoes in their backyard, there are a few measures you can take. First, do your best to contact them, and ask them to clean up rubbish & debris, and ask them to treat or drain standing water.

US and Canadian snowbird properties are some of the worst offenders, especially if there are no responsible and active property managers and the owners are absent. Snowbird-owned properties are notorious mosquito breeders because NOB folks love water features like pools, fountains, decorative troughs, hollowed-out stones and potted plants. These collect rainwater – and it only takes a tablespoon of residue that doesn’t dry to breed A.ae mosquitoes.   The problem is aggravated by local property managers who are hesitant to do anything new or different, particularly if the owner has not directly ordered it.


Property managers are notorious for letting fountains and pools get super nasty for months, and then making a big effort the week before the owner returns to clean things up. Consequently, the owners suspect nothing, because they return to sparkling pools, while their neighbors suffered with months of mosquitoes.

In a case such as this, do your best to educate your neighbors directly and voice your concerns, and get their property manager’s contact information from them. (Send them this article!)

Finally,  Mexican health authorities really have no authority to enter properties without the owner’s consent.

Dr. Fry had a friend in the centro who persistently tried to get various government agencies to help with their New York City neighbor’s algae/mosquito swamp-like swimming pool, with no success.   In a case such as this, we suggest discreetly throwing a nylon stocking with granulated/powdered chlorine, which would work for a while, or with the aforementioned Paris Green, which would work nearly permanently.

Traps and Repellents

Mosquito traps (that emit CO2 from propane) or the UV light+fan ones work well at trapping just mosquitoes, but the ones that use a UV light attractant and electrical grids indiscriminately kill lots of many types of bugs, thereby reducing bat populations. This is not a good thing when you want to reduce the mosquito population.

There are, of course, many ways that mankind has devised to keep mosquitoes at bay. The easiest methods to come by here in the Yucatan are in the grocery stores: sprays and pumps of liquid repellant, mosquito coils that burn like incense and mosquito "cards" that are inserted into special holders that plug into the wall and emit mosquito hormones that keep them away. There are candles with citronella to burn on your patio. This year, we’ve also seen mosquito bracelets that emit citronella to keep the wearer mosquito-free.

There are devices that emit sounds that are supposed to repel mosquitoes, and there are bug lights, as well as "tennis rackets", nifty devices that allow you to swat at the mosquitoes and give them a deadly electrical shock when you get one (these, we hear, are available at the Chinese restaurant on Calle 47 at Parque Santa Ana).

Nothing is failsafe, and in our experience, using multiple methods is probably a good idea.

The Dengue Transmission Chain

Dengue Transmission occurs as a chain of events. Break just one link of the chain and Dengue transmission ends.

  1. Uninfected female A. ae. finds febrile Dengue infected Human.
  2. Female A. ae. bites the febrile Dengue Human.
  3. Female A. ae. mosquito hides and rests for 3-4 days.
  4. Dengue virus moves into the A. ae. mosquito’s salivary glands.
  5. Female A. ae. mosquito lays eggs in water.
  6. The now Dengue-infected female A. ae. mosquito finds human and bites human.
  7. Mosquito eggs hatch and develop into adults in 7 days at Yucatan temperatures.
  8. Newly hatched female mosquito has sex with male mosquitoes.
  9. Male mosquitoes feed on nectar and plants.
  10. Newly hatched A. ae. female mosquitoes search for their first blood meal, and if successful, they bite a human for their first blood meal, continuing the cycle.

If you break or interrupt any single link in this chain of mosquito activity, (1-10), Dengue transmission stops, which makes mosquito control our best proven way to control the spread of Dengue virus.

How to Eliminate Mosquito BreedingRepellant

Eliminating or treating mosquito breeding sites is highly effective and our best current solution. As you read through this list, you will undoubtedly find a few things to do that you haven’t thought of yet, as well as more than a few suggestions for some of your neighbors.

  • Clean up rubbish piles & drain standing water
  • Drill holes in the bottoms of all outdoor flower pots
  • Cover household drains tightly, or treat with ammonia to kill larvae
  • Maintain sufficient free-Chlorine levels in swimming pools to kill larvae
  • Dispose of old tires, buckets, & plastic items that retain even small amounts of rain water
  • Drain unused swimming pools to total dryness, and consider using a larvacide like Copper Sulfate to treat any rain water that accumulates during the owner’s absence.
  • Treat fountains and pools with chlorine, copper, or add mosquito-eating fish, like Gambusia or guppies, mollies, and other live-breeding fish.
  • Flush unused guest bedroom toilets weekly, or treat, or seal them with plastic wrap
  • Flush all sink, shower or floor drains inside the house weekly,  and cover or seal unused drains

Don’t Worry… Be Happy

And after all this, don’t worry about it too much. After living here for over eight years, we know a few people that have contracted Dengue while living here. We also know a lot of people that have not. Some of our friends who came down with Dengue suffered greatly, and some seemed to have a mild case. Take the precautions listed above and enjoy yourself. If you feel you might have Dengue, get yourself to a doctor as soon as possible and get tested. If you do have it, stay hydrated and stay in touch with your doctor. Luckily, the doctors here are not only competent, but they give you their cel phone numbers to call if you need them. Take advantage of the great healthcare here if you need it, and otherwise, don’t worry! Enjoy the Yucatan!

References:
(1) “The Devil’s Disease, Dengue Fever”, P. McGuire, Johns Hopkins Public Health, Spring 2010 Ed., 2010, pp 16-21.
(2) Dengue: guidelines for diagnosis, treatment, prevention and control — New edition, WHO and the Special Programme for Research and Training in Tropical Diseases (TDR), 3rd Edition report, ISBN 978 92 4 154787 1, 2009.
(3) A Timeline for Dengue in the Americas to December 31, 2000 and Noted First Occurrences”. J Schneider, MPH and D Droll, Pan American Health Organization: Division of Disease Prevention and Control, June, 2001, 99 1-20.

(4) Mexico Worried by Rise in Hemorrageic Dengue by Mark Stevenson, Associated Press, July 21 2010.

(5) USEPA Pesticides: Reregistration: Temephos RED.  http://www.epa.gov/oppsrrd1/REDs/temephos_red.htm 

Links of Interest:

Center for Disease Control and Prevention – About Dengue in Tropical and Subtropical Regions

About Dengue in the United States by Ali Khan

Baroso Pool Supply is at Calle 51 #532-A x 74 y 76 in the centro

 


Editor’s Note: The facts of this article were painstakingly gathered by Dr. Steven Fry who lives in Merida, Yucatan with his wife. Dr. Fry is a doctor of Chemistry, and spent 27 years in Environmental and Public Health in the United States before coming to Merida. He was the first Western scientist invited into the former Soviet Union, (after its break-up) to evaluate public health & environmental issues in Ukraine, as a consultant to the US Agency for International Development. His wife is a laboratory director at UADY, specializing in Dengue and West Nile Viruses – and Dr. Fry developed a bit of a background from helping evaluate her data, and helping write her dissertation on Dengue and West Nile Viruses.  She is a full-time UADY researcher working on various joint projects with the Dept. of Health and the Bill and Melinda Gates Foundation.

You can read more about Dengue and more writings by Steven Fry at his website. Specific Dengue articles can be read here and here.

Information about Paris Green here (Foundations of Community Medicine, 2′nd Ed.  page 160) and here (Malariology: page 283).


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41 Responses to “Everything About Dengue Fever”

  1. Excellant Article! Thank you for posting!

  2. Dear Working Gringos & Drs Fry,

    Great article! It definitely gives one something to work with. I would like to know if it has been translated into Spanish in its entirety. I would like to send it to Spanish-speaking friends in Mérida who might not be so well-informed about the precautions that can be taken around one’s property.

    Thank you for the fine article.

  3. If it so nasty, I am surprised that they have not come up with a vaccination for it. Since it is a virus, like the flu, then one would seem that a vaccination for the different forms could keep individuals safe from dengue infection.

    I have watched the Houses of Merida series and have notice the beautiful doors to patios which are totally open and have cringed, being the phobe I am about mosquitos and things of the sort, without screen doors to be pulled to close the areas. Outside is nice, mosquitos are not.

    I have an immune problem where I do not manufacture enough B lymphocytes which combat viruses and bacteria, so I have to take immune globulin infusions, but I am sure that the dengue just might be the death to me, especially with repeated cases. We have been looking at the Yucatan and Panama as places in which to retire, and both places have Dengue. Surely, someone must be working on a vaccination for this, but we don’t have one for West Nile as of this moment and mosquitos carrying it have been found in the Harris Country (Houston) area in Houston after recent rains. We try to be careful in regard to the possibility for standing water, and our little lizards around the doors go nuts feasting on any bugs if we turn on the lights at the doors.

    Thank you for this informative and enlightening article.

  4. OOOUCH!

  5. I have had dengue once (about 2 years ago). the experience was like a two-week long case of flu… very painful muscles and joints, lethargic with no energy. I spent most of the two weeks in my hammock and drank lots of water and took Tylex CD (paracetamol and codeine) which is by prescription only in the Yucatan. I took the caps about every 8 hours to help with the pain. When I finally realized that I might have dengue (well into the two weeks) I googled the symptoms and the treatment and found that I was self-treating with the same treatments that probably would have been given by an MD. I never did get a blood test but the MDs with whom I subsequently spoke felt that I did have dengue based on my symptoms. As an aside, EVERY health clinic or facility that I have entered in the past 10 years in Mexico, Central and South America had a dengue poster outlining (in much less detail) the gist of your article. Another possible mosquito deterrent that I am currently trying is raising neem (nim) trees on my property. The tree is native to India and is currently being cultivated in the Yucatan. It has many natural pesticide properties. Indian friends have told me that just the presence of the tree discourages mosquitos. We’ll see.

  6. Thanks to Dennis about the information regarding the Nim trees.

  7. What a great article. If it isn’t in there, it doesn’t exist!

    Regarding Bti – Haven’t found it for sale yet in Merida, but surely it is. We’ve brought the “dunks” down (small cakes like smallish donuts) and put them in standing water puddles and water holding tanks in hacienda-like place. Within a week, the numbers of mosquitos diminished significantly. Within two weeks, there were hardly any to be found. The dunks last 30 days, according to the packaging, as they slowly release Bti into the water.

    The other things work too, but Bti is the least toxic to all other creatures, hardly being toxic at all. So, if birds, lizards or animals drink the water, they won’t be harmed. Birds and lizards are important allies against mosquitos, so we like to keep them around.

    Dengue is mostly a “city disease.” As the transmission information above shows, if any link is broken, transmission does not occur. In rural settings, transmission is less likely due to the distance between households. It becomes harder for the female to bite an infected person and encounter an uninfected person to bite in the limited timeframe.

    Great job on this entry for Yucatan Living. And much of the same applies to Malaria, West Nile, and other mosquito-born illnesses.

  8. Brenda Thornton” said on August 24th, 2010:
    “If it so nasty, I am surprised that they have not come up with a vaccination for it. Since it is a virus, like the flu, then one would seem that a vaccination for the different forms could keep individuals safe from dengue infection. ”

    Brenda,
    There are currently 2 major trials underway for Dengue Vaccines, with preliminary results expected in 2012 and 2014, but experts are not holding out much hope for the success of either trial for several reasons. An effective vaccine would need to treat all four strains of Dengue Virus (DV-1 – DV-4), and all 4 current Dengue Virus strains would have stop mutating for any vaccine to be useful.

    Dengue Virus started out as a single strain, and it has already mutated into 4 unique strains with different properties, so, it is unlikely that the Dengue Viruses will stop mutating any time soon (DV will likely remain a moving target). Since an infection with one Dengue Virus strain potentiates the patient’s immune for worse reactions to future Dengue infections from the other DV strains, providing immunity to one strain would likely expose the vaccinated patient to worse infections from the other 3 strains.

    For these reasons, Denis Larsen’s approaches to reduce mosquito habitats make the best sense for now. Cheers, Dr. Fry

  9. If I may, would like to assist you making your Spanish a bit user friendly…

    Ayudame, por favor. (Please help me)

    Creo que tengo una infeccion del Dengue (I think I am infected with Dengue Virus)

    Es aqui el lugar para las pruebas del Denge? (I understand you can test for Dengue here)

  10. Hello,
    I went to Baroso to try and buy Copper Sulfate — they told me it was carcinogenic, and while they sold it, didn’t use it themselves in pools they treated, and were required to warn people before they sold it..
    Anyone have any information about this?
    Thanks!
    Jorge

  11. Firedog,
    Thank you for the kind reply and suggestions.

    Background: Instead of translating English phrases, I asked the Director of UADY’s Dengue Testing Clinic and Dengue Laboratory what exact Spanish phrases and statements would work best, when a person requests help to get free Dengue Testing, when they enter UADY’s Centro de Investigacines and stop at the front desk. Dra. Loroño Pino suggested the phrases offered in the article. My apologies if they aren’t a word-for-word translation of the English phrases.

    Spanish’s 14 verb tenses and its reflexive verbs still confuse me, so, I have to rely on other’s help. Cheers, Dr. Fry

  12. Thanks to Dr. Frye. The mutations would be a big problem, and I should have thought of that. I suppose one could get one of those large-brimmed hats and put a mosquito net on it when one had to be outside in the dusk or evening.

    Otherwise, be vigilant and do what was suggested by the article.

  13. This is a serious problem.
    Mosquitoes transmit more than just dengue.
    Thank you Yucatan Living for doing your part!

  14. Jorge,
    The copper levels I recommended above are very safe and are actually below the United States and Canada’s Recommended Daily Dietary amounts of Copper. I recommended 5 teaspoons of Copper Sulfate Penta-Hydrate (the pretty blue salt that Barroso sells) for a 50,000 liter pool, which gives a concentration of 0.18 ppm free copper.

    You have to drink 5 liters of this copper treated pool water every day to get your US & Canada minimum daily required nutritional levels of copper. Even if you added 150 teaspoons of copper salts to you 50,000 liter pool, you would have less copper than tap water in the typical German home ( 4.8 mg/L Cu(II) ):
    World Health Organization:
    http://www.who.int/water_sanitation_health/dwq/chemicals/copper.pdf page 12

    The USEPA allows 1.2 mg/L of Copper in children’s drinking water:
    http://water.epa.gov/infrastructure/drinkingwater/schools/upload/2006_1_11_schools_lead_sqrg_lcr_schools.pdf

    The amount of copper I have prescribed has been recommended by US State and Federal agencies for algae control for decades, and at just 0.18 mg/L Copper, (5 tsp. per 50,000 liters), the amount I recommended is 7 times LOWER than the US clean drinking water standards.

    Finally, one might note that Yucatan’s high pH water slowly oxidizes our copper plumbing, so, if the Barroso guys were right, millions of Yucatecans would be getting cancer from our hard water inside our copper pipes, and millions of Germans would be getting cancer, since their drinking water has 27 times more copper than I advised.

    Hope these descriptions have helped ease your mind.
    Dr. Steven Fry

  15. First of all, I have done my own research and this article is excellent. Along with the care of pools, fountains, plants and other things around the house and ideas to help your neighbors cut their mosquito breeding, screens, and the use of one of the CO2 devices, I think I would feel pretty secure regarding Dengue and avoidance of it.

  16. Friends who spent considerable time living in Thailand and visiting Vietnam said they are convinced that there is one true solution: fans.

    Not only are fans more comfortable in humid weather, but weak-flying mosquitoes cannot make headway in breezy conditions.

    They used pedestal fans and table fans on the floor, oscillating. Ceiling fans are ok for comfort, our friends told us, but they don’t make sufficient air currents near your ankles and there’s where mosquitoes love to attack. So, they simply kept 3 or 4 fans going at a good enough speed to keep the mosquitoes away in whichever room they were in at the time. And, they used mosquito nets for sleeping, of course. (with fans as well — it is surprising how warm it can become under a mosquito net!)

    I have no idea if this actually works as a sole solution as claimed, but consider swampy areas of coastal Thailand and Vietnam. You can’t do much about “your neighbor’s mosquitoes” there!

    Perhaps there’s something to it. One more thing to try.

  17. CasiYucateco,
    Good point about Thailand. They should know about mosquitoes, because they are often the country in the world with the highest rates of Dengue Fever infections.

    Sidelight: Past studies in Thailand have found that 98% of the Aedes Aegypti mosquitoes have Dengue infections when found in Thai homes that also have a patient with an active Dengue infection.

    This means that Thailand (and Yucatan to a lesser degree) has a big problem with other family members getting Dengue after just one person in the house gets Dengue.

    Why? After the first person gets Dengue, that person then infects all the other mosquitoes (98%) in the house with Dengue, and these newly-infected mosquitoes then go on to bite and infect the other family members

    There is only one way to break that cycle:
    When the first family member get’s infected, it is important to immediately attempt to kill ALL mosquitoes in the house, by carefully spraying every room (leaving the windows and doors shut on every room after spraying for 1-2 hours to improve eradication effectiveness). It is particularly difficult to kill all the mosquitoes inside a bedroom, because they hide under the bed, under the dresser, up on the ceiling, and especially in our hanging clothes, since they are attracted to the residual body odor that lingers in our clothes closets. You have a better chance of killing the mosquitoes if you vigorously move the hanging clothes around while you are spraying with mosquito spray, especially spraying the areas between/in and under the clothes.

    We’ve used Mata Mosco successfully. (Mosco = Mosquito, Mosca = House Fly).

    Since Thailand typically has some of the worst rates of Dengue infections, they might need more fans – or your friends need to spread the word of their discovery? ;-}
    Dr. Steven Fry

  18. Just guessing, but I imagine that most Thai’s have a hard time affording 3 or 4 fans in every room of the house to keep the air moving at all levels. I’ve tried to imagine it and keep getting a headache thinking of all the oscillations. On the other hand, it might help with the comfort level in high humidity. . .

  19. Thank You Dr.S. Fry!

  20. I must say, after hearing American after American carry on about how Mexico “just can’t seem to get it together” to get this dengue situation under control, I find it rather vindicating to read that these snowbird homes are some of the worst offenders.

  21. Is there any danger to pets?

  22. Hi Joanne,
    There is no danger from Dengue virus to typical pets like cats and dogs. Research studies have found that rhesus monkeys can get Dengue virus infections, and these monkeys can maintain serum Dengue viral titers at levels that could infect Aedes Aegyptii mosquitoes that could go on to infect the monkey’s human family members.

    Do you have any monkeys as pets?
    Dr. Fry

  23. I am trying to locate a mosquito delito (co2) machine in Merida and have been unsuccesful. Does anyone know where I can buy one?

    Claudia

  24. What manufacturer of CO2 based traps were you interested in?

    According to their website: http://support.mosquitomagnet.com/store_locator/International/Default.aspx?sltCountry=MX
    Mosquito Magnet brand traps for Mexico are handled by:
    Global Expansions LLC
    81 West Street – D2
    Attleboro, MA 02703
    Mexico
    Phone: (508) 222-2238
    Fax: (617) 890-0876
    Email: info [at] globalexpansions [dot] info
    Contact: Esteban A. Arrondo

    Their traps work well for the first year, but reports from around the web say that 1 in 3-4 of them have problems, and Mosquito Magnets official policy is that they do not sell parts for repairs. Broken units must be shipped back to the USA for repair only by their official techs. Typical repair costs on past broken units have been quoted at over $200, without shipping, for even minor power supply problems. Their rechargable battery powered units seem to have less problems here than their 120V units, since the 120V units are plugged in 24/7, making them susceptible to the fluctuating power issues common here in Yucatan.

  25. This is a very helpful article and I learned a lot of new information. I have a couple of questions. Is there a dengue season or can someone get dengue anytime of the year. Also, I heard that dengue mosquitoes are only active during the day. Is this true? Thank you for a very good article.

  26. webergirl,
    Dengue infections tend to increase during the rainy season here, with infection rates often peaking in October – November, but Dengue is present year round in Yucatan. The Aedes aegypti mosquitoes are most active in the morning, when they are out seeking blood meals. They do bite at other times during the day, particularly in shaded places, like darting out from under a desk to bite a foot or ankle, but at much lower frequency. They can show some low activity in the evening, and they basically are not active at all during the night, so, the mosquito you hear buzzing in the dark is most likely a Culex (no Dengue or Malaria risk).
    Dr. Fry

  27. Dr. Fry…..I was wondering if bug spray was a good idea when going out and about….I will be spending sometime in the Yucatan in March around Merida. When I was in Playa del Carmen last year I didn’t notice any mosquitos……

  28. In the interest of full disclosure, I want to point out to everyone that Dr. Steven Fry, while he has “Dr.” in front of his name and is an extremely intelligent and well-read gentleman, is not a medical doctor. If anyone has questions or concerns about their own health, we at Yucatan Living want to encourage you to seek the advice of a physician.

    Thank you!!

  29. Peter,
    Yes, all three major health organizations, WHO, PAHO, and CDC advocate using insect repellent on exposed skin when visiting areas where Dengue is endemic. Since Aedes Aegypti like to bite feet and ankles, pay special attention to protecting these areas with clothing (socks and long pants) or with insect repellents.
    Dr. Fry

    **As as aside to Working Gringos’ observation: It is true that I am not a physician, but I have over 25 years of professional experience and training in working on public health. I was the first Western scientific expert invited into the former Soviet Union to evaluate public health, water, and food quality issues after the break-up of the Soviet Union. I have worked with public health and environmental programs in 37 states, Canada, Scotland, Italy, Mexico, and Ukraine. More recently, I have spent the past 5 years here in Mexico, with efforts to study Dengue Virus and West Nile Virus and supporting leading Dengue control research programs. In the interest of full disclosure, I am employed part-time by the Universidad Autonoma de Yucatan working under a Gates Foundation grant to study Aedes Aegypti mosquitos and Dengue. I mention these things, because most US physicians have little or no training or experience in mosquitoes or Tropical Medicine or Dengue. Most experts in the field consider that PAHO, WHO, and CDC recommendations are generally better than the information provided by US or Canadian physicians, because these physicians have little experience with Dengue and Tropical Medicine.

  30. Thank you, Dr. Fry!! We’re lucky to have you in our city and on our website…

  31. Ankle biters of all types really bug me!

    Thanks to Steven Fry, PhD, for sharing his massive volume of information. And, if I am not mistaken, his wife is a medical doctor involved in Dengue research as well? (I think).

    What’s the news on any possible treatments, vaccines, or other progress against the virus that causes this? Can I drink a cup of sugar water that immunizes me soon?

  32. CasiYucateco,
    Excellent questions.

    As posted above in the comments, there are trials underway for a Dengue vaccine with results expected in 1-2 years, but because:
    1. Dengue virus mutates somewhat rapidly, it is difficult to hit a moving target; and
    2. the presence of 4 major strains (DV1, DV2, DV4, & DV4) requires immunizing for each strain, likely requiring 4 different solutions.

    Alternately, Dengue transmission has many links, where breaking one link stops the chain. There is very promising research underway in Australia demonstrating the ability of a Wolbachia bacteria to infect Aedes Aegypti mosquitoes. The Wolbachia bacteria interferes with the reproduction of the Dengue Virus inside the A. Ae mosquitoes. After a female A.Ae mosquito bites a febrile Dengue infected human, the female mosquito usually serves as an incubator for Dengue Virus, but since the Dengue Virus is unable to replicate inside the Wolbachia-infected female mosquitoes, a critical link of the Dengue transmission cycle is broken. The Wolbachia bacterial infection is then passed from the mother mosquito to her eggs, and her progeny are then infected with the Wobachia bacteria – making them also unable to transmit Dengue Virus. The Australians are currently conducting field trials to prove the efficacy of infecting natural populations of Aedes Aegypti with Wolbachia to permanently produce natural Aedes Aegypti mosquito populations that cannot transmit Dengue Virus.
    http://www.nature.com/nature/journal/v476/n7361/full/nature10356.html#access

    So, while human vaccine trials do not look promising, mosquito alteration trial results do look very promising for controlling Dengue Virus transmission. If successful, we are left with the potential ethical issues of messing around with Mother Nature. If producing lines of permanently Wolbachia-infected mosquitoes is troubling, consider gardener’s frequent & common usage of Bacillus thuringiensis (Bt) bacteria to control garden pest larvae.

    What do you all think?
    Dr. Fry

  33. Thanks so much for this. We will be coming to Puuc region and Merida in early January and will be outside most of the time. You say to cover your skin as much as possible, but in Minnesota the mosquitoes bite through clothes. Do these mosquitoes do that also, or are they smaller or do they have shorter probosces, to make that less of a problem? Should we wear thicker shirts, pants, and socks rather than thinner? Many thanks for any help!

  34. Hi sara,
    Fortunately, Minnesota’s mosquitoes are not like ours.

    Even light cotton clothing gives protection from Aedes Aegypti (and other Yucatecan mosquito) bites.
    Enjoy your trip!
    steve

  35. Dear Dr. Fry,

    I am working on a charity case for a local Mexican person. A woman was bit by some kind of poisonous insect 3 years ago when she was asleep. Her legs were swollen like an elephant’s legs and she went to the hospital and had the infection removed. However, her whole body became very stiff. Almost paralyzed. She went from a normal person to a cripple sitting in a wheelchair. Now she has become blind. I have been searching the internet to see if there is any poisonous insect in this region that could do such damage to a person.

    Do you have any idea what kind of insect that would do this? Does anyone know of any similar case like this in the Yucatan region?

    Thank you for any information someone might have or anyone you can refer me to.

    Dr. Huynh

  36. Could this be West Nile?

  37. West Nile Virus (WNV) has different symptoms than Dengue Virus (DV). Like Dengue, WNV is also a Flavirus, but the human immune system makes different Immunoglobulin (IG) proteins and enzymes (IGG and IGM isotypes) when fighting a WNV infection than the IGG and IGM results for Dengue Virus infections.

    Since the major clinical symptoms are different (no bleeding, rash, retro-orbital pain etc for WNV), the IGG, IGM, & Blocking ELISA results are different, and the DNA sequencing results are different for DV infections vs. WNV infections, then it is doubtful that local lab test results are confusing WNV infections for Dengue.

    The UADY lab I work for found WNV in birds migrating to the Yucatan in 9 years ago, but there were no significant numbers of human infections. Since the corvids are hit hard by WNV, we lost most of our crows here in Yucatan to WNV at that time.

    There is Cache Virus (another Flavivirus) circulating in Yucatan, but Dengue remains the main Flavivirus health concern.

  38. Just published official Sanofi study results for 4,000 children studied, actually show that the study group had the statistically similar rates of Dengue infections as the control group.

    These were Phase 2 results, and there is a small (but highly unlikely) possibility that the Phase 3 results will show more promise.

    This points to the need for all of us to continue cleaning-up mosquito breeding grounds, as there is no vaccine in the works to treat all the strains of Dengue virus infections.

    There is one trial running that might treat 1 of the 4 strains circulating here in Yucatan.

  39. Dr. Fry … Can you tell us where to buy ammonia, which you suggest using in a solution to get rid of mosquitoes? I can’t locate it here, tho years ago there was a drugstore down near the central market on calle 54 which sold it in double-capped plastic containers. I’ve not tried looking down there again, assuming the drugstore no longer is there.

    Miguel Kiton/Merida

  40. Hi Miguel,
    You can buy ammonia in the cleaning products sections of larger grocery stores. Ammonia is also sold down on C. 54 and C. 54A, between C65 and C67, and possible on C. 56 – basically in the farmacias around the Mercado Lucas de Galvez.
    Dr. Fry

  41. Where can I get lavender oil (aceite de lavanda) in Yucatan? It is supposed to be very good for fighting mosquitos, for controlling itching, and for skin health. We are in Yucatan for the whole summer, and the mosquitos are horrible in the pueblos.

    Gracias.

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