As Wet Season Comes, as Well the Risk of Dengue Infection!!


There is no vaccine available against dengue, and there are no specific medications to treat a dengue infection. This makes prevention the most important step, and prevention means avoiding mosquito bites if you live in or travel to an endemic area.

The best way to reduce mosquitoes is to eliminate the places where the mosquito lays her eggs, like artificial containers that hold water in and around the home. Outdoors, clean water containers like pet and animal watering containers, flower planter dishes or cover water storage barrels.  Look for standing water indoors such as in vases with fresh flowers and clean at least once a week.

The adult mosquitoes like to bite inside as well as around homes, during the day and at night when the lights are on. To protect yourself, use repellent on your skin while indoors or out. When possible, wear long sleeves and pants for additional protection.   Also, make sure window and door screens are secure and without holes. If available, use air-conditioning.

If someone in your house is ill with dengue, take extra precautions to prevent mosquitoes from biting the patient and going on to bite others in the household.  Sleep under a mosquito bed net, eliminate mosquitoes you find indoors and wear repellent!

Epidemiology

Dengue fever (DF) is caused by any of four closely related viruses, or serotypes: dengue 1-4. Infection with one serotype does not protect against the others, and sequential infections put people at greater risk for dengue hemorraghic fever (DHF) and dengue shock syndrome (DSS).

Transmission of the Dengue Virus

Dengue is transmitted between people by the mosquitoes Aedes aegypti and Aedes albopictus, which are found throughout the world.  Insects that transmit disease are vectors.  Symptoms of infection usually begin 4 – 7 days after the mosquito bite and typically last 3 – 10 days.  In order for transmission to occur the mosquito must feed on a person during a 5- day period when large amounts of virus are in the blood; this period usually begins a little before the person become symptomatic.  Some people never have significant symptoms but can still infect mosquitoes.  After entering the mosquito in the blood meal, the virus will require an additional 8-12 days incubation before it can then be transmitted to another human. The mosquito remains infected for the remainder of its life, which might be days or a few weeks.

In rare cases dengue can be transmitted in organ transplants or blood transfusions from infected donors, and there is evidence of transmission from an infected pregnant mother to her fetus.  But in the vast majority of infections, a mosquito bite is responsible.

In many parts of the tropics and subtropics, dengue is endemic, that is, it occurs every year, usually during a season when Aedes mosquito populations are high, often when rainfall is optimal for breeding.  These areas are, however, additionally at periodic risk for epidemic dengue, when large numbers of people become infected during a short period.  Dengue epidemics require a coincidence of large numbers of vector mosquitoes, large numbers of people with no immunity to one of the four virus types (DENV 1, DENV 2, DENV 3, DENV 4), and the opportunity for contact between the two.  Although Aedes are common in the southern U. S., dengue is endemic in northern Mexico, and the U.S. population has no immunity, the lack of dengue transmission in the continental U.S. is primarily because contact between people and the vectors is too infrequent to sustain transmission.

Dengue is an Emerging Disease

Image: Lab Confirmed cases of Dengue in South America

The four dengue viruses originated in monkeys and independently jumped to humans in Africa or Southeast Asia between 100 and 800 years ago.  Dengue remained a relatively minor, geographically restricted disease until the middle of the 20th century.  The disruption of the second world war – in particular the coincidental transport of Aedesmosquitoes around the world in cargo –  are thought to have played a crucial role in the dissemination of the viruses.  DHF was first documented only in the 1950s during epidemics in the Philippines and Thailand.  It was not until 1981 that large numbers of DHF cases began to appear in the Carribean and Latin America, where highly effective Aedes control programs had been in place until the early 1970s.

Global Dengue

Today about 2.5 billion people, or 40% of the world’s population, live in areas where there is a risk of dengue transmission see WHO/Impact of DengueExternal Web Site Icon. Dengue is endemic in at least 100 countries in Asia, the Pacific, the Americas, Africa, and the Caribbean. The World Health Organization (WHO) estimates that 50 to 100 million infections occur yearly, including 500,000 DHF cases and 22,000 deaths, mostly among children.

Image: Dengue in the world

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