Monkey sentinels form our first line of defense against yellow fever & other diseases that have killed millions
RIO DE JANEIRO, Brazil; SINGHUDURG, India––Panic-driven monkey massacres are contributing to human illness and death, and perhaps could help to spark global epidemics, warn Brazilian health officials.
A related “monkey fever” meanwhile raging in parts of India has recently jumped into new and very different habitat, also showing potential to spread far and wide.
At issue is simian susceptibility to Flaviviridae viruses, carried by mosquitoes and ticks. Killing upward of 5,000 people per year, worldwide, flaviviruses are as deadly to South American and Asian monkeys as to humans.
Monkeys go naked
But because monkeys live outdoors, without clothing, they tend to be more exposed to mosquito and tick bites than humans, despite their protective fur.
Because monkeys don’t get vaccinations against flaviviruses and do not get hospital care when sick, monkeys tend to die sooner than humans when bitten by infected mosquitoes and ticks, too.
When scavenging urban monkeys fall dead in streets and yards just as humans start becoming ill, people with little knowledge of how diseases spread tend to blame the monkeys instead of the invisible viruses and the mosquitoes and ticks that carry them.
Believed to have evolved originally in Africa, the flavivirus family appears to spread globally in several waves coinciding with the beginning of global trade in the Age of Discovery circa 500 years ago, the growth of the slave trade from Africa to the Americas, intercontinental movements of troops and refugees associated with various wars, and the global rise of passenger jet travel.
Each wave moved mosquitoes, ticks, eggs, and larvae into favorable new habitats.
Yellow fever, the deadliest flavivirus-carried disease in terms of numbers of human deaths, “came to South America with the first slaves at the end of the 16th century,” the late arborovirus researcher Jack Woodall told ANIMALS 24-7 in 2008, “and took a while to get established in the jungle. So unlike African monkeys, the howlers [and other New World monkeys] have not had several million years to adapt.”
Woodall, who in 2004 cofounded the Program for Monitoring Emerging Diseases (ProMED), died in 2016 after spending most of six decades combatting flavivirus-carrried diseases, and––even more––ill-informed responses to these and other diseases that tend to exponentially increase disease-related suffering instead of helping to bring the diseases under control.
Flavivirus-carried diseases reached the Indian subcontinent, Southeast Asia, and China in separate, less easily historically defined waves, but with similar effect: Asian monkey species, like humans but unlike their African simian cousins, have yet to evolve strong resistance.
In Asia, as in South America, lack of resistance puts monkeys in double jeopardy when flavivirus-carried diseases break out. Often, if the diseases themselves don’t kill the monkeys, fearful humans do.
The fear is understandable. Flaviviruses endemic to mosquitoes carry yellow fever, dengue fever, Japanese encephalitis, West Nile virus, and Zika virus.
Flaviviruses endemic to ticks carry tick-borne encephalitis and Kyasanur Forest disease, along with many lesser-known ailments.
But urbanized monkeys living off refuse and handouts among human cities and settlements are often the most ubiquitous and reliable sentinels warning of flavivirus outbreaks. When monkeys die, flavivirus experts know, it is time to aggressively vaccinate humans throughout the region––and to escalate mosquito and tick control efforts, too.
By the time humans begin dying, typically a flavivirus outbreak is already widely distributed and difficult to stop.
In the nightmare scenario that inspired Woodall and others to form ProMED, haunting the membership ever since, infected humans might fly to all parts of the world before falling ill. Though flavivirus-carried diseases tend to be transmitted only by particular types of mosquito or tick, the Aedes aegypti mosquito most closely associated with yellow fever has already colonized airports and surrounding habitat all over the world.
An Aedes aegypti mosquito need only bite one human with yellow fever, then bite another human, who is in turn bitten by other Aedes aegypti mosquitoes, to start spreading a pandemic outbreak.
Targeted vaccination drives where monkey deaths have occurred can prevent that worst case scenario.
Killing monkeys kills the warning
Unfortunately, reported Medical Xpress and ProMED on February 11, 2018, “Fears of spreading yellow fever are behind the illegal killing of scores of monkeys in Rio de Janeiro,” as well as in other Brazilian cities.
In the first month of 2018, Medical Xpress said, “238 monkeys have been found dead in Rio state, compared to 602 in all of 2017,” according to the Rio de Janeiro sanitation service, which had begun a campaign against the killings, occurring at the rate of as many as 20 per day.
Among the dead monkeys, Rio Veterinary Center coordinator Fabiana Lucena said, “69% showed signs of human aggression, mostly having been beaten to death and some poisoned.” By comparison, in 2017 “the proportion found killed by humans was 40%. The rest died of natural causes.
“The monkey is a victim”
“People should understand that it’s the mosquito transmitting the yellow fever virus. The monkey is a victim,” Lucena emphasized to Agence France-Presse, “and if there are no more monkeys in the countryside, then mosquitoes will come to attack people.
“Monkeys show us where the virus has gone,” Lucena explained. “To have a more effective vaccination campaign, we have to identify the zones where monkeys are dying from yellow fever. When people kill them, the virus is harder to trace.”
“Similar attacks on monkeys have been registered in Sao Paulo and Minas Gerais states, which have seen the worst impact of yellow fever this year,” said Medical Xpress.
“The Green Line, a platform for issuing complaints by telephone in the Rio municipality for environmental crimes,” recounted Medical Xpress, invited witnesses to monkey killings to “call or send in photographs and videos, guaranteed anonymity, to be “sent to the Command of Environmental Police and the Commission for Environmental Protection.”
“Killing monkeys is not a solution”
Observed ProMED-mail viral diseases moderator Tom Youill, “Although there is no indication of the species of dead monkeys mentioned in the above reports, there is serious conservation concern about the deaths of some monkey species, both due to yellow fever infections and to people killing them. The massive deaths of brown howler monkeys that have occurred are bad news. Fortunately, the endangered northern muriqui monkeys do not seem to be affected.
“Previous reports indicate that brown howler monkeys and masked titis are the non-human primates most affected in this yellow fever outbreak,” Youill wrote. “However, the buffy-headed marmoset is also mentioned. This is a rare species of marmoset endemic to the rainforests of southeastern Brazil and occurs in southern Espírito Santo and possibly northern Rio de Janeiro, and its distribution extends into Minas Gerais, the very areas where yellow fever has been occurring.
“Unfortunately,” Youill concluded, “there is no feasible way to halt yellow fever virus transmission among these non-human primates. Killing them is not a solution. One hopes that enough individuals will survive for the species to recover.”
“Highest observed in decades”
Reported the Pan American Health Organization/World Health Organization (PAHO/WHO) epidemiological update for February 16, 2018, “Between January 2016 and January 2018, seven countries and territories of the Region of the Americas reported confirmed cases of yellow fever,” including Bolivia, Brazil, Colombia, Ecuador, French Guiana, Peru, and Suriname: almost the whole of the Amazon drainage basin, excluding only southern Venezuela.
“The number of human cases and epizootics collectively reported in this period in the Region of the Americas is the highest observed in decades,” continued PAHO/WHO.
According to the Secretariat of Health Surveillance at the Brazilian Ministry of Health, there were 846 yellow fever cases resulting in 260 deaths from July 1, 2017 to March 6, 2018, a steep increase from 597 cases resulting in 190 deaths during the same time frame a year earlier.
“Major increase in yellow fever in Sao Paulo & Rio”
Though PAHO/WHO noted that “This figure is lower than what was reported for the same period of the previous year, reported cases in the states of São Paulo and Rio de Janeiro have significantly exceeded the numbers reported in the preceding season, 2016-2017, with cases reported in areas near major cities.”
Most of the increase occurred in Mairiporã, a São Paulo suburb; in the cities of Valença and Teresópolis, each a little over an hour’s drive from the city of Rio de Janeiro; and in Belo Horizonte, which had not reported any yellow fever in 2016-2017.
These “correspond to areas with documented epizootics in non-human primates,” PAHO/WHO noted.
While the yellow fever flavivirus killing monkeys and humans in Brazil is carried by mosquitoes, chiefly Aedes aegypti, the flavivirus killing monkeys and humans and driving panic in India is carried by ticks.
Commonly called “monkey fever,” the ailment is formally known as Kyasanur Forest Disease, named after the forest in Karnataka state, in western southern India, where the disease was first medically identified in 1957.
Kyasanur Forest Disease can afflict any mammal. Cases have been discovered, but are relatively difficult to recognize, in sheep, goats, and cattle. Kyasanur Forest Disease may be deadliest to monkeys, however, among whom the death rate may be as high as 10%––about the same as it is among humans whose infections go untreated.
Outbreaks spread north
The most recent Kyasanur Forest Disease outbreak, reported The Express, “is believed to be spreading from an outbreak that started in three villages in Sindhudurg,” Maharashtra state, hundreds of miles north of the Kyasanur Forest and north of most previously known cases.
The outbreak was discovered through investigations of monkey deaths.
At most recent report, the outbreak had infected 332 people, killing 19 of the victims. At least 40 monkeys died in the same areas.
A second current Kyasanur Forest Disease outbreak has hit the Wayanad district in Kerala state, well south of the Kyasanur Forest.
Other outbreaks have occurred throughout the southern “cone” of India.
Risk raised by global warming
Monkeys are protected in India to some extent by the popularity of Hanuman, the Hindu monkey god, as well as by wildlife conservation laws.
Kyasanur Forest Disease outbreaks, however, have stoked political pressure from agriculturalists frustrated by crop-raiding monkeys to have at least some monkey species reclassified as “vermin,” who may be killed with impunity.
Because the ticks who carry Kyasanur Forest Disease thrive during the dry season, which has become steadily longer in recent years due to global warming, outbreaks are expected to increase in frequency and intensity.
But Kyasanur Forest Disease was not expected to spread into the parts of India, like Maharashtra, that were already significantly dryer than the regions where it was previously found. The Maharashtra outbreak suggests that translocated ticks may be able to take Kyasanur Forest Disease not only into other regions, but perhaps to other nations and even continents, where other species susceptible to ticks––deer, for example––could become the ticks’ primary hosts.