Opinion: Who’s Afraid of Yellow Fever? Why We Should Be

Opinion, by Jack Woodall

RIO DE JANEIRO, BRAZIL – There hasn’t been a yellow fever epidemic in Rio for over one hundred years, when the rich escaped to the mountains in Petropolis, Teresopolis and Friburgo in the mosquito season. It’s only in the Amazon, and Brazil does not recommend vaccination for people living in or visiting the South-East. So why worry now?

Here’s why. There is a big yellow fever epidemic currently raging in Angola, southwest Africa, and the world`s supply of vaccine has run out – WHO has sent it all there.

BioManguinhos/FioCruz in Rio is one of the only four yellow fever vaccine producers in the world, and it has been having production problems, so it is not easy to boost global stocks quickly.

Whatever is produced will be needed in Angola, which is struggling to immunize everyone just in the capital, Luanda, let alone all of its 24 million population.

Infected Angolans have already spread it across the border as far as Kinshasa, capital of the Democratic Republic of the Congo, and arrived in Mauritania and Kenya. There are thousands of Chinese working in Angola, and at least ten have now arrived home for treatment, the first time in history that yellow fever has been confirmed in Asia. If it spreads from there to tropical Asia, there will never be enough vaccine.

What most people don’t know is that there are a lot of Angolans coming every year to Brazil, and the more who arrive here unvaccinated, but have been exposed to yellow fever in Africa and may be carrying the virus, the greater the risk that they will infect Rio mosquitoes, allowing them to transmit yellow fever to residents and tourists. If that happens, Rio`s already creaky public health system will be overwhelmed, and there will not be enough vaccine available to cope with demand.

The only hope of prevention will then be mosquito control. The mosquito species that is spreading dengue, chikungunya and now Zika in Rio is the black-and-white striped Aedes aegypti, the same one that causes urban epidemics of yellow fever.

It breeds in small collections of rainwater in garden and street trash, and uncovered tires, animal watering bowls, flower pots and vases, axils of plant such as bromeliads, rainwater barrels and cisterns, and in puddles on construction sites.

Outdoor fogging of the Olympic stadiums and other premises only kills mosquitoes exposed that day, not those sheltered indoors by homeowners and shopkeepers closing up to keep the smell out, and they are quickly replaced by hatching larvae.

Mosquito fish are two inches long, too big for use except in cisterns and unused swimming pools. Breeding trillions of transgenic mosquitoes to release and sterilize the wild ones, which is being tested in Brazil, or mosquitoes infected with deadly (for them) bacteria or a fungus, would take months to scale up.

Spreading hormones, mosquito-killing bacteria or special oil to kill the larvae in the water can help, but if property owners would only clean up their premises, and allow sanitation workers access to empty or abandoned properties – of which there are a surprising number in Rio – there would be a lot less cases of dengue, chikungunya and Zika for the health system to cope with.

Since Aedes aegypti is a day-biter, bed nets are no protection except to prevent spread from bed-ridden patients. The only personal protection advised is to wear clothing that exposes as little skin as possible – not popular when bound for the beach – and slathering on DEET-containing repellent.

If everybody had pitched in and cleaned up their own act (premises) years ago, we would have had much less dengue in Rio, let alone chikungunya and Zika. Those diseases have low death rates, but unvaccinated yellow fever victims have only a 50/50 chance of surviving. So if you aren`t already vaccinated, go to the airport and do it now – it needs ten days to take effect.

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Jack Woodall PhD was a Visiting Professor and director of the emerging diseases laboratory in the Institute of Medical Biochemistry, Center for Health Sciences, UFRJ, Rio de Janeiro, now retired.