Howler monkeys serve as beacons for where yellow fever is spreading

Once again, fears loom in Brazil of a possible comeback of yellow fever. What’s worse: urban outbreaks could occur quickly. Authorities have raised the alert after a monkey in the São Paulo zoo died of the disease last week. Monkeys do not transmit the disease, but rather serve as beacons for where the virus is present. As the zoo is right in the heart of the country’s biggest metropolis, there is cause for concern. The World Health Organization has issued a warning that the country could experience a third outbreak in as many years.

According to the latest data from the Ministry of Health, there were 37 confirmed cases of yellow fever infections between July 2018 and February 7, 2019, with nine deaths. Another 118 patients are under investigation. Infections are concentrated in two states: São Paulo and Paraná. “While it remains early to determine if this year will have the high number of cases observed [in 2016-2017 and 2017-2018], there are signs that the virus is continuing to spread towards the south of the country and to areas where immunization rates are low,” said the WHO.

Current <a href="">policies</a> in Brazil mean that <a href="">vaccination</a> is only required in certain remote areas. Some, however, disagree with the Brazilian government’s vaccination practices against the disease. In countries such as Ghana, for example, vaccination is <a href="">compulsory</a> for both residents and visitors. “In Brazil, they’ve drawn a line that supposedly demarcates risk. We vaccinate people on one side and don’t vaccinate people living on the other side,” Thomas Monath, a yellow fever expert at biotech firm NewLink Genetics, told </span><a href=""><i><span style="font-weight: 400;">Science</span></i></a><span style="font-weight: 400;"> in 2017. “But mosquitoes aren’t observing that demarcation.”</span></p> <p><span style="font-weight: 400;">Three out of every four confirmed cases have happened in areas considered to be risk-free.</span></p> <p><span style="font-weight: 400;">After the death of the monkey in São Paulo Zoo, the city&#8217;s administration launched a door-to-door vaccination campaign in southern neighborhoods. At least 200 agents were sent to visit 13,000 homes looking for people who have yet to receive the fever shot. According to municipal officials, 78 percent of the city has already been vaccinated.</span></p> <h2>A hike in confirmed cases</h2> <p><span style="font-weight: 400;">While authorities recommend the vaccination of all people in states of the South and Southeast, all of them are still below the target to immunize at least 95 percent of residents between 9 and 59 years old. Roughly 36.9 million people in the Southeast (where the three most populated states are—São Paulo, Minas Gerais, and Rio de Janeiro) have not taken a yellow fever shot. In the South, 13.1 million remain unprotected.</span></p> <p><span style="font-weight: 400;">Between January and August 2018, the number of wild yellow fever cases jumped by 600 percent—with over 500 people contracting the disease and at least 178 dying from it. While the 2017 outbreak was mainly concentrated in rural areas of Minas Gerais, the virus has now quickly spread around São Paulo&#8217;s countryside and to the south. </span></p> <p><span style="font-weight: 400;">A </span><a href=""><span style="font-weight: 400;">study</span></a><span style="font-weight: 400;"> by the Adolfo Lutz Institute shows that monkey migration through forest corridors—caused by the effects of climate change on the animals&#8217; natural habitat— are to blame for the quick return of a disease that haunted Brazil in the late 19th and early 20th centuries. The virus that circulates in the Amazon quickly spread among monkey families of the Atlantic Forest, which are not immune to it. And the effects have been devastating for many species. Researchers calculate that in 2017 at least 1,300 monkeys died of yellow fever in Espírito Santo—and other 5,000 in São Paulo.</span></p> <p><span style="font-weight: 400;">&#8220;Diseases such as yellow fever can decimate entire primate populations and should call out attention to side effects of climate-related problems,&#8221; said biologist Laurence Culot to Fapesp. </span></p> <p><span style="font-weight: 400;">Besides the virus, monkeys have to deal with another menace: panicked humans. Last year, over dozens of primates were killed by people after monkey infections were first reported. Methods varied from hunting them down with clubs or rifles to poisoning. However, as authorities say, killing the animals that serve as beacons for the virus puts humans at greater risk.

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BY Gustavo Ribeiro

An award-winning journalist with experience covering Brazilian politics and international affairs. His work has been featured across Brazilian and French media outlets.