In difference to malaria, which vector is a parasite, dengue fever is a viral disease. It’s hosts are exclusively primates, mostly humans and some kinds of mosquitoes of the family aedes, who transfer it. There are four different subspecies of the virus.
Mosquito larvas in a washing basin in Cambodia. Images by Asienreisender, 2013
Dengue fever is a very dangerous and painful disease. It is also an emerging disease, in fact the fastest dispersing disease in the world transfered by mosquitoes. In the fifty years between 1960 and 2010 dengue cases rose up thirty fold worldwide. In the ten years between 2000 and 2010 the number of cases doubled. That has to do with the expansion of the vector mosquito, what is in Southeast Asia (mostly) the Asian tiger mosquito, in general mosquitoes of the aedes family. This mosquito kind thrives in urban regions, and it’s very adaptable. Since urbanisation is rampant in Southeast Asia, the Asian tiger mosquito has a rapidly growing habitat. But it’s also worldwide spreading out. Globalization promotes the outspread of the tiger mosquito and the disease. Increased mobility as travel activities, population growth and global warming play a role as well.
Particularly the Philippines and Laos are in the center of the emerge, but also Thailand, Malaysia, Singapore and Vietnam have all reported an increase in cases.
The World Health Organization (WHO) estimates between 50 to 100 million annual cases of dengue worldwide, of whome half a million suffer a heavy course of disease and 22.000 people die; most of the victims are children. In Asia more than 90% of the heavy course of the disease hit children. The magazine ‘Nature’ wrote in it’s April 2013 issue that even 390 million people get infected annually, referring to the studies of the scientific authors of the article.
Dengue is endemic in 110 countries in the tropical and subtropical regions of the earth; 75% of the dengue cases appear in the Asia/Pacific region.
Dengue fever is commonly also called the ‘breakbone disease’ or ‘dandy fever’.
Transfer
The disease is mostly transfered by the Egyptian tiger mosquito, also known as dengue mosquito or yellow-fever mosquito and, here in Southeast Asia, by the Asian tiger mosquito (lat. Stegomyia albopicta, aedes albopictus). There are some other mosquitoes who transfer the disease, particularly in New Guinea and in the south Pacific (the Polynesian tiger mosquito).
The circle of reproduction is similar to those of other mosquito-born diseases. A female mosquito sucks blood from an infected person and gets the virus in it’s stomach. If the virus concentration is high enough, it can befall the mosquito’s stomach cells and reach it’s own blood circulation and contamine the mosquito’s saliva. The extrinsic incubation time inside the mosquito is eight to ten days, means that the virus is then mature and harmful. Next time when it’s biting someone, the infection is transfered to him or her. That’s because at any bite a mosquito does, first it’s injecting some saliva into the victims blood. A single bite of an infected mosquito is sufficient to transfer the disease, but not necessarily does. The virus can also be transfered from the mosquito to it’s lavaes.
Although the mosquito gets itself infected by the dengue virus, there are no harming effects for the mosquito.
Dengue can’t spread directly from one person to another one. But, if there is someone around who has dengue fever it is most important to protect everybody from the mosquitoes around, particularly the patient. They can transfer the virus from the infected person to other people around.
Dengue can also be transfered by blood transfusions and organ donations if the donator was infected himself.
The risk of an infection is highest in the rainy season (monsoon), for the mosquitoes then find the most breeding places and florish. The tiger mosquitoes prefer living indoor in urban regions and their daily peak periods of biting are around sunrise and up to two hours later and around sunset. Though, it can bite at any time of the day.
Course of the Disease
After getting bitten by a mosquito and infected, dengue has a latent period between three and fourteen days. Most of the cases are mild and not to distinguish from a normal flu. One get’s fever (up to 40 degree C) with ague, headache, eye- muscle- and limbpains. It comes together with a rash. After three to seven days it’s easing off. Though, in two to four percent of the cases the course of disease continues heavy. A ‘dengue hemorrhagic fever’ (DHF), also called ‘dengue shock syndrome’ can appear. One to five percent of the heavy cases are lethal.
Dengue hemorrhagic fever is an acute shock syndrom with uncontrollable inner and outer bleedings; the blood circulation breaks down, abdominal pain, fever and headache, dehydration, brain caused spasms, coma, bloody vomiting, bleeding gums, a swollen liver and many more symptoms appear.
The shock occurs two to six days after infection with sudden collapses, cool clammy extremities, weak thready pulse and blueness around the mouth, blood spots in the skin, spitting blood, blood in the stool, bleeding gums and noise bleeding. It can lead to pneumonia and heart inflammation. The mortality rate at this stage is announced by the WHO by between 2.5% with proper medical treatment up to twenty percent, without. Letal cases are mostly among children.
The disease is very painful. The acute phase lasts between one to two weeks, but can extend much longer (four to six weeks). If the infection is survived, the patient is immune against all four dengue viruses for a short time and for the certain virus which caused the acute disease a live long.
When suffering the first typical symptoms it makes sense to have it checked by a doctor to make certain what it exactly is.
Know…
This is only a part of the illustrated article ‘Dengue Fever’. Read the whole article on Dengue Fever by Asienreisender.
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