Nov. 20, 2011 Update: 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 ….
Dengue: transmitted between humans in the Americas by our friends(?) Aedes aegypti.
An estimated 50 million dengue infections occur annually, and approximately 2.5 billion people live in dengue endemic countries.
The affected countries include México and almost all other countries in the Tropics. Fatality rates from extreme Dengue Virus infections (DHF & DSS) have ranged from 1%-3.5% in Dengue endemic areas. Yucatán and along the Gulf coast of Mexico are Dengue endemic areas (areas maintaining Dengue Virus).
The WHO and the Special Programme for Research and Training in Tropical Diseases (TDR) has released their latest guidelines on Dengue Virus. Their presentation is available in a 160 page format (for those who enjoy a bit of light reading). The 3′rd Edition report contains all their updates since the 1997 Second Edition.
This article is a summary of bits and pieces (for the rest of us) taken directly from the report, so, I have put things extracted directly from their report in italics, along with my observations in normal type and I will give no other citations or references.
Dengue Virus infections come in several forms:
- most people get mild infections with few symptoms and possibly a short duration low fever;
- others get some combination of intense fever, pain behind the eyes, body rash, extreme pain in their bones and joints, and mild nose bleeds; (these two are called “Dengue Virus Infections” or “Dengue Fever”)
- WHO reports that a few (3% – 5%) get the potentially fatal symptoms of “Dengue Hemorrhagic Fever” (DHF) of Dengue Shock Syndrome (DSS), where DHF causes bleeding from the eyes, gums, nose, under the skin, or into the GI tract, vomiting, and black stools. **DHF rates in Mexico have been increasing the past 3 years, with up to 50% of Dengue Virus cases exhibiting DHF or DSS symptoms.
Hydration (at least 5 glasses of liquid per day for adults) and bed rest are the main treatments for the first two types of symptoms. In the cases of DHF or DSS Intravenous rehydration is the therapy of choice; this intervention can reduce the case fatality rate (for DHF) to less than 1% of severe cases. The main symptoms of DHF and DSS requiring hospitalization are listed below.
Symptomatic dengue virus infections were grouped into three categories: undifferentiated fever, dengue fever (DF) and dengue haemorrhagic fever (DHF). DHF was further classified into four severity grades, with grades III and IV being defined as dengue shock syndrome (DSS).
If you get a suspected Dengue Virus infection, you can get tested in Mérida for roughly $400 pesos at the laboratory across from the Zoo, on Izaes and Calle 59: El Centro de Investigaciones Regionales “Dr. Hideyo Noguchi“. The NS1 tests for Dengue virus protein work very well during the first 3 days of fever, so, it is good to get tested before the 5′th or 6′th day of fever. The evaluations also include seeing a Physician and lots of good advice. There is a physician (Dr. Nubia Rivero) there every day between 7:00 AM and 9:00 AM who specializes in Dengue cases.
Merida is the center for advanced medical care for 500 miles around, and we are very lucky to have one of the top laboratories in the Developing World that does this testing and research = yet another reason to move to Merida.
The treatments for mild Dengue infections are the same (whether you get tested or not): bed rest, hydration with water juices etc ( at least 5 glasses per day for adults), reduce fevers greater than 102º F / 39º C, using cool baths, cool showers, alcohol rubdowns, and possibly Tylenol. There are no pills, no antibiotics, no magic elixers that have been shown to work in treating Dengue cases.
NSAIDs like aspirin, Advil, Motrin, Alleve, ibuprofen, etc and blood thinners should be completely avoided because they inhibit clotting which can cause death if the patient proceeds to DHF or DSS symptoms.
Getting Waiting to get Dengue Virus testing here in Merida before Day 5 – Day 6 of fever, also fits with the possible progression to Dengue Hemorrhagic Fever (DHF) or Dengue Shock Syndrome (DSS). If you get positive NS1-test results for Dengue, then you know to pay special attention to your Dengue symptoms to watch for DHF or DSS. Dengue infections can proceed to DHF or DSS around Day 4 – Day 7 of fever, so, patients should be monitored carefully for symptoms of bleeding or shock or abdominal symptoms during this period, where DHF or DSS causes bleeding from the eyes, gums, nose, or into the GI tract. Patients with severe bleeding symptoms or shock** should be taken to a hospital immediately for IV hydration treatments.
**Several definite indicators of need for immediate hospitalization:
- black stools (evidence of GI bleeding)
- coffee-ground vomiting (congealed blood in vomit)
- not passing urine for more than 4–6 hours
- heavy menstruation/vaginal bleeding
- Frequent vomiting
- Severe abdominal pain
- Drowsiness, mental confusion or seizures
- Pale, cold or clammy hands and feet
- Difficulty in breathing
Conditions like these require hospitalization: IV rehydration and possible blood transfusions.
~ Does avoiding these possible consequences make it worth installing screens, getting rid of old tires, draining flower pots, and cleaning up other mosquito breeding habitats in your and the neighbors’ properties?
Dengue viruses occur as 4 different serotypes: DEN-1, DEN-2, DEN-3, and DEN-4, and we have all 4 serotypes circulating here in Yucatán.
From 2001 to 2007, more than 30 countries of the Americas notified a total of 4,332,731 cases of dengue. The number of cases of dengue haemorrhagic fever (DHF) in the same period was 106,037. The total number of dengue deaths from 2001 to 2007 was 1299, with a DHF case fatality rate of 1.2%. The four serotypes of the dengue virus (DEN-1, DEN-2, DEN-3 and DEN-4) circulate in the region. In Barbados, Colombia, Dominican Republic, El Salvador, Guatemala, French Guyana, Mexico, Peru, Puerto Rico and Venezuela, all four serotypes were simultaneously identified in one year during this period.
During 2001–2007, a total of 545,049 cases, representing 12.5% of dengue in the Americas, was reported, with 35,746 cases of DHF and 209 deaths. Nicaragua had 64 deaths (31%), followed by Honduras with 52 (25%) and Mexico with 29 (14%). Costa Rica, Honduras and Mexico reported the highest number of cases in this period. DEN-1, -2 and -3 were the serotypes most frequently reported.
The dengue virus enters via the skin while an infected mosquito is taking a bloodmeal, so Dengue is transmitted from Dengue infected humans to Aedes aegyptii (A. ae) female mosquitos. After the previously uninfected female A. ae mosquitos rest & digest their blood meal for 2-3 days, they then lay eggs. Next the now-Dengue-infected females return to bite other humans – infecting those humans.
It is worth noting that the WHO study results only include Dengue cases that were confirmed by laboratory tests, while Dengue experts routinely report that less than 10% of Dengue patients get tested, so, all numbers of infections reported here are likely in reality 10X higher.
There were just over 2,000 Dengue virus infections reported for Yucatán in 2009, which means there were most likely over 20,000 Dengue infections in Yucatán in 2009. Dengue has been circulating continuously in Mexico since the 1970′s, when it was re-introduced from Cuba. Dengue had been eliminated from Western Hemisphere for roughly 12 years, except for Castro’s Cuba, where they denied its presence, refused to treat for mosquitos, and jailed & imprisoned Cuban scientists who dared to report its presence.
Probable Indications & Signs of Dengue Infections:
•Live in / Travel to dengue endemic area.
and 2 of the following criteria:
• Nausea, vomiting
• Aches and pains
• Tourniquet test positive
• Any warning sign (see next list)
• Abdominal pain or tenderness
• Persistent vomiting
• Clinical fluid accumulation
• Mucosal bleed
• Lethargy, restlessness
• Liver enlargement 2 cm
• Laboratory: increase in HCT concurrent with rapid decrease
in platelet count
Our local Dengue experts add the following warning signs that are unique to Dengue infections:
- pain behind the eyes (retro-orbital pain),
- pain in the bones and joints (hence Dengue’s other name: “Break-Bone Fever”), and
- Mild hemorrhagic manifestations like petechiae (small dots of bleeding under the skin) and mucosal membrane bleeding (e.g. nose and gums) may be seen.
CRITERIA FOR SEVERE DENGUE SYMPTOMS
Severe plasma leakage leading to:
• Shock (DSS)
• Fluid accumulation with respiratory distress
• Severe bleeding as evaluated by clinician
• Severe organ involvement
• Liver: AST or ALT =1000
• CNS: Impaired consciousness
• Heart and other organs
…an average Dengue episode represented 14.8 lost days for ambulatory patients and 18.9 days for hospitalized patients.
DENGUE IN INTERNATIONAL TRAVEL
Travelers play an essential role in the global epidemiology of dengue infections, as viraemic travellers carry various dengue serotypes and strains into areas with mosquitoes that can transmit infection. … Travellers often transport the dengue virus from areas in tropical developing countries to developed countries…
Fortunately, Dengue virus is not communicable from person to person. Dengue virus is transmitted by only one type of mosquito: Aedes mosquitoes, exclusively Aedes aegypti in our part of the world. The A. ae. mosquitos get infected by biting a human with an active Dengue fever. For this reason, mosquito control is the key to controlling and limiting Dengue’s spread. Typical studies find that 90%-95% of A. ae. mosquitos collected in the homes of a Dengue fever patient have Dengue Virus.
This means that one of the first actions when a person has a suspected Dengue infections is to spray the patient’s home to kill all mosquitos, to protect the home’s other occupants from getting Dengue infections.
A. ae. mosquitos love to live, rest, and digest blood meals, in dark cool places, like under the bed and in clothes closets (attracted by our smell on our clothes), so, focus mosquito spraying efforts on low, cool, dark places. We treat our rooms by spraying thoroughly with commercial mosquito spray, with the windows and doors tightly closed, and then we retreat to the next room/area spraying it, and continuing that process until the whole house is treated and then left tightly closed-up for 1 – 2 hours – and we go somewhere else in the meantime.
The A. ae. mosquito is a tropical and subtropical species widely distributed around the world, mostly between latitudes 35 0N and 35 0S. These geographical limits correspond approximately to a winter isotherm of 10 0C. Ae. aegypti has been found as far north as 45 0N, but such invasions have occurred during warmer months and the mosquitoes have not survived
the winters. Also, because of lower temperatures, Ae. aegypti is relatively uncommon above 1000 metres.
The immature stages are found in water-filled habitats, mostly in artificial containers closely associated with human dwellings and often indoors. Studies suggest that most female Ae. aegypti may spend their lifetime in or around the houses** where they emerge as adults. This means that people, rather than mosquitoes, rapidly move the virus within and between communities.
Mosquito Facts & Dengue and Mosquito Control:
**A. ae. mosquitos love fresh water and prefer human blood – making them a “City Mosquito”, not a marsh mosquito, and not a jungle mosquito. A. ae. mosquitoes can fly very fast, unlike other mosquitos, and they inject a little anesthetic with their saliva when biting, so you don’t feel them bite.
A. ae. mosquitos can breed in as little as a tablespoon of residual rainwater, so, you can best eliminate Dengue and A. ae. mosquitos by eliminating their breeding grounds, getting rid of anything around your property that collects standing water: old tires, old crockery, plastic rubbish, brush piles, drill holes in the bottom flower pots, etc.
We cover our unused toilets and drains with Saran wrap – which permanently block mosquitoes, since chlorine dissipates over time. One other friend uses ammonia in his unoccupied house drains & toilets, because it maintains its potency longer.
If you have a fountain or other water feature: A variety of fish species have been used to eliminate mosquitoes from larger containers used to store potable water in many countries, and in open freshwater wells, concrete irrigation ditches and industrial tanks. Guppies and mollies breed like mad, and they eat mosquito larvae, and Gambusia are especially good at eating mosco larva. Or you could treat the water with chlorine every 7 days.
Dengue infected A. ae. adult mosquitos can live up to 30 days, and once the females are infected by biting an infected human, they can continue to infect other humans for the rest of their little lives.
Ae. aegypti is one of the most efficient vectors for arboviruses (like Dengue Virus) because it is highly anthropophilic, (loves humans,) frequently bites several times before completing oogenesis, and thrives in close proximity to humans.
Once the A. ae. mosquitos’ eggs are laid, the eggs typically take 7 days to hatch (depending on water temperature) and develop into adult mosquitos. This means that it is important to treat or change exposed fresh water at least once every seven days = time to wash the pet’s water bowl? (since the mosquito eggs can lay dormant & dry for months to years?)
Typically, these mosquitoes do not fly far, the majority remaining within 100 metres of where they emerged. They feed almost entirely on humans, mainly during daylight hours, and both indoors and outdoors. A. ae mosquitos tend to feed in the morning and in the evening. They typically bite people’s feet, ankles, and lower legs so, it can help to treat your lower legs and feet with repellent or wear socks and long pants.
Since A. ae mosquitos do not feed late at night and since they are also silent, that buzzing you hear in the middle of the night is not a A. ae female mosquito: it’s likely a Culex instead…
There is accumulating evidence that insecticide-treated window
curtains (net curtains hung in windows, over any existing curtains if necessary) and long-lasting insecticidal fabric covers for domestic water-storage containers can reduce dengue vector densities to low levels in some communities – with prospects for reducing dengue transmission risk.
A current Mérida study using curtains shows a reduction of moquitoes in homes without screens, but the homeowners keep tying back the curtains – and they do not like having their doorways covered (blocking breezes) , or they add their own other personal decorative curtains – all of which reduce curtain/net/ITM efficacy – which means that insecticide treated bed netting and ceiling net traps work better.
Well, I’m pooped from writing, and I’ve gone through all 160 pages of the WHO report, I’ve included a bunch of addition information that I’ve learned while living with a Dengue researcher, and think I’ve covered all the important stuff.
except a few items:
- Scientists used to think it took 10 days or more between being bitten by a Dengue infected mosquito and the onset of fever & symptoms, but there have been recent reports of as short as a 4 day incubation period between the insect bite and the Dengue infection…
- A single dengue infection sets the patient up for future more intense dengue infections, with the symptoms getting worse with every subsequent infection, with the possibility of death increasing dramatically with every new infection.
- Each dengue infection confers a very brief immunity (3-4 months) to ONLY that strain of Dengue, but that single infection leaves the patient even more susceptible to more serious symptoms from the other 3 remaining Dengue strains (serotypes).
Please give a shout if you see something I missed…
hint: The female shown above (note the long proboscis not present on males) is a very young A. ae mosquito – as the distinctive black and white markings fade with age….
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Disclaimer: This information is not meant as legal advice. It is for educational and informational purposes only. Government policies vary between States and offices, and Mexican Government officials have broad discretion in how they individually enforce policies, so, your personal experiences may vary. See a professional for advice on important issues.
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Feel free to copy while giving proper attribution: YucaLandia/Surviving Yucatan.
© Steven M. Fry
Read-on MacDuff . . .