Tuesday, February 2, 2016

Zika, Chikungunya, Dengue

The three names in the title designate viroses which are attributable to the dissemination through mosquitos of the species Aedes Aegypti.  Dengue is the oldest from the three diseases and, at least in Brazil, the first cases were reported between 1851 and 1853 with an epidemic episode in 1923. The name of the disease comes from one of the symptoms, joints pain, which leads people to walk with broken movements, like a puppet.

 Dengue was virtually extinct n Brazil during the campaign to eradicate Yellow Fever, which targeted the vector, by eliminating its habitat  n urban areas. Dengue returned to Brazil in the 1980's, probably by the dissemination of the vector from neighboring countries which had less success in eradicating it. At the time, however, I heard an alternative explanation: it stated that populations of the vector remained in the forest areas and that the advance of the urban areas (deforestation) lead to the reintroduction of the vector in the cities. Anyway, the mosquito returned and, with it, the Dengue fever. There is no vaccine (contrary to yellow fever) and so, the only way to control the disease is by controlling the vector.
Since the 1980's we "know" we cannot leave sources of still water exposed to the ambient, because these are preferred sites for reproduction of the mosquito. It is amazing. Last January I was  in the interior of the state of Bahia, an open water reservoir was filled by rain water and in the next day it was already swarming with mosquito larvae. This also shows why it is so difficult to solve the problem, I guarantee about 95% of the population takes the proper measures to avoid mosquito reproduction, the problem is the other 5%.
Dengue is usually not critical, it leads to severe fever (40°C), rashes in the skin, the already mentioned joint pain and some other symptoms, which are similar to influenza. The particularity, however, is that in a second infection there is the risk of development of the hemorrhagic dengue fever and this is very dangerous. There are vaccines in development, but none has been approved to date (as far as I know).
The development of a Dengue vaccine, however, would be no relief to the problem, because of the two other viroses, Chikungunya and Zika. As far as I know, Chikungunya is similar to Dengue (but the virus is different), Zika started as a third virose associated with the mosquito, but supposedly with less severity.
The situation escalated in the second half of 2015, when reports of an increase in cases of microcephaly in the northeast region of Brazil raised the suspicion the there was association with the development of Zika infection in the pregnant women in the first stages of the pregnancy. The brown press started to raise suspicion of relation with the introduction of transgenic mosquitos in the environment, this introduction was an attempt to control the vector.
Although it is possible, the relation between Zika and the microcephaly was not proven, I just read a report telling that only a fraction of pregnant women which had microcephalic babies reported Zika infection during pregnancy. There is the need to investigate this link, and, especially, to identify the mechanism by which a viral infection would affect a baby in the womb (as far as I understood, babies are protected against diseases in the mother). Any pregnant woman traveling through an affected area, however, should take extreme precaution against the mosquito bites.
An important question, however, is our vulnerability to viral infections. Bacterial infections can be combated by antibiotics, micoses can be successfully combated by medicines, even protozoa can be combated by other medicines, but the standard response of a physician to a person with a viral infections is: wait for the body to combat the illness. As we saw in the last Ebola outbreak in Africa, there are powerful antiviral medicines, but these are expensive and their collateral effects are severe.
Here in Brazil we keep trying to control the vector. The situation is critical, but not debilitating. People are not walking ill in the streets and, although the statistics are scaring, not everyone gets these diseases. The scientific community, however, should help, in particular the biologists and the biochemists, to investigate these viruses and their infection mechanisms, and the industry should work in the development of efficient medicines against viral infections.
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