West Nile virus isolated for the first time in Brazil

Researchers isolated the virus in tissue from a horse with encephalitis in Espírito Santo State. The study was presented during the annual meeting of the Brazilian Society for the Advancement of Science.

By Elton Alisson, in Maceió  |  Agência FAPESP – West Nile virus has arrived in Brazil. Researchers at Evandro Chagas Institute (IEC) in Belém, Pará State, have reported the first isolation of the virus in central nervous system tissue from a horse that died of encephalitis (inflammation of the brain) on a farm in Espírito Santo State.

A fast-track report was published in the journal Memórias do Instituto Oswaldo Cruz. Coauthor Pedro Fernando da Costa Vasconcelos, a researcher at IEC, spoke about the study on July 23 during a presentation on arboviruses in Brazil at the 70th Annual Meeting of the Brazilian Society for the Advancement of Science (SBPC), held at the Federal University of Alagoas (UFAL) in Maceió.

West Nile virus belongs to the same viral family as Zika. Both emerged originally in Africa and are transmitted by mosquitoes. West Nile virus arrived in the Americas via the United States in the late 1990s and has since spread to Central and South America.

“When the first cases of infection in the US were reported, we began monitoring birds in the wild, the virus’s main hosts, with the aim of isolating it in Brazil, but we obtained only scant serological evidence,” Vasconcelos told Agência FAPESP.

“Now, we’ve finally succeeded in isolating the virus in tissue from a sick horse on a farm in Espírito Santo, which notified the authorities that animals were dying from encephalitis and asked us to identify the cause.”

The researchers also performed whole-genome sequencing of the isolate and concluded that the virus found in the sick horse had the same genotype as West Nile viruses isolated in the US, as well as Argentina and Canada, where cases of infection have also been reported. “This shows that the virus has spread throughout the Americas, probably by migratory birds,” Vasconcelos said.

It entered the Americas via New York, he explained, when the Bronx Zoo imported infected animals (mainly geese and ducks) from Israel and other countries.

The animals were bitten by Culex pipiens mosquitoes, which spread the virus across the US. C. pipiens is a close relative of the Southern house mosquito C. quinquefasciatus, which in Brazil transmits elephantiasis (also known as lymphatic filariasis). 

“West Nile virus spread very quickly in the US,” Vasconcelos said. “It was first detected in New York City on the East Coast in 1999, and by 2002, there were reports from practically all parts of the continental United States.”

After the US, there were reports of infection by the virus in Mexico, Venezuela, Argentina and Brazil, where the first case of infection in humans was reported by researchers at IEC (the patient was in Piauí State).

“In North America, West Nile virus has also been detected in recipients of cornea, kidney and heart transplants,” Vasconcelos said.

Most infected humans are asymptomatic or have few symptoms, such as fever, headache, fatigue, muscle pain, vomiting, loss of appetite and skin rash. In approximately 1%, however, the virus affects the central nervous system, causing a neurological disorder that inflames the brain and meninges and may lead to death.

“We don’t anticipate many cases of severe infection by West Nile virus in Brazil similar to those reported in the US, given the absence of dengue in the US, which doesn’t vaccinate the population against yellow fever, and of other flaviviruses that are widespread in Brazil, such as Zika, chikungunya, dengue and yellow fever,” Vasconcelos said.

Because the Brazilian population has a high level of immunity against flaviviruses, and because extensive cross-reactivity has been observed between flaviviruses, the incidence of severe infection by West Nile virus will be much lower than in the US, Vasconcelos added.

“There could be minor local outbreaks in Brazil, especially in areas where other arboviruses haven’t occurred frequently or at all, such as the South region,” he said.

However, West Nile virus could be a grave threat to animal health in Brazil, especially for horses and birds, according to Vasconcelos. In the US, for example, high mortality among crows was reported until the virus stabilized.

“Brazil may also see large numbers of deaths among birds and livestock such as horses, although we have a vaccine against West Nile virus in animals,” he said.

The article “First isolation of West Nile virus in Brazil” by Lívia Caricio Martins, Fernando da Costa Vasconcelos et al. is published in Memórias do Instituto Oswaldo Cruz and can be read at memorias.ioc.fiocruz.br/article/6488/0332-first-isolation-of-west-nile-virus-in-brazil.