Wednesday, February 3, 2016 at 6:24AM
Ian Read

History doesn’t repeat itself, but it can be uncannily similar.  In 1849, a strange disease began to spread among the ships and within the harbor area of Bahia.  By the time the Imperial government recognized it as yellow fever, it had spread widely up and down Brazil’s coast.  Like the Zika virus (and dengue and chikungunya), yellow fever is spread by the Aedes aegypti mosquito.  For the next six decades, Brazilians suffered enormously from yellow fever epidemics, although there were clusters of epidemic years and sometimes as much as a decade without many cases.  The disease was mostly concentrated in the larger urban areas of the coast but spread to smaller cities and inland areas.  For example, Campinas, a town in the São Paulo highlands that was not far from the rapidly expanding coffee zone and a magnet area for European migrants, was struck by a horrendous yellow fever epidemic in 1889. Only by the first and second decade of the 1900s, and after scientists discovered the disease vector was the this mosquito (rather than miasma, or vitiated air), did Brazilian public health officials begin to make progress in diminishing this disease through vector control. Brazilians put great effort into vaccines as early as the 1880s, but a yellow fever vaccine was not developed until 1936 (today vaccine development is still slow, but not this slow).

Dengue, yellow fever, and (probably) Zika have sylvatic reservoirs

Oswaldo Cruz and other public health officials orchestrated a wide reaching campaign that sent thousands of health workers door to door and yard by yard to eliminate the mosquito’s breeding ground.  The Aedes aegypti usually depends on humans because it does not breed in water that collects on the ground.  Human containers such as cisterns, animal troughs, barrels, flower pots, buckets, and tires create idea spaces of its larvae to hatch.  By sealing, removing, or treating this water the mosquito cannot breed and spread the virus.  The collective health campaigns in Brazil’s cities were often quite effective, and the number of yellow fever cases in cities like Rio de Janeiro fell from several thousand to less than a hundred in only two years.  Unfortunately, yellow fever has a sylvatic or jungle cycle, reproducing among other species of mosquitos that live in the forests.  For this reason, the disease cannot be eradicated, but removing the urban vector greatly improved public health in Brazilian cities by 1915.

Breeding sites of the Aedes egypti

Today there is global attention on the likely link between microcephaly and the Zika virus.  Many articles erroneously miss the fact that its disease vector, the Aedes aegypti, typically breeds in artificial containers found in people’s yards.  Additionally, the attention is often on developing a vaccine, a prospect that is unlikely to occur soon.   Taking a lesson from the past, Brazilian officials are correct by putting their energy into vector control, although insecticides may be less effective than some hope.  By reducing this mosquito from urban areas, not only will Zika be diminished, but also dengue, another serious (and relatively new) problem in Brazil.  Another option is to suppress the mosquito population through genetic manipulation.   Geneticists may insert genes into mosquitos so that the offspring of male mosquitos die before adulthood or female mosquitos cannot fly and therefore breed.  This strikes most people as risky and scary, but there is little evidence that “frankenmosquitos” will take over the world, especially since these manipulations are not transmitted.  I am disheartened to see the rumors circulating, in some cases among major (tabloid) newspapers such as the UK Mirror, that genetic manipulation of mosquitos is causing Zika, a mistruth that may prevent an effective vector control solution to several dangerous diseases. 

Article originally appeared on Era of Epidemics: A Spatial Approach to Disease and History in Imperial Brazil (http://empireofbrazil.org/).
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