Local transmission of Japanese encephalitis documented in Africa for first time

Researchers have documented the first evidence of locally transmitted Japanese encephalitis in Africa.

According to a letter in The New England Journal of Medicine, the mosquito-borne infection was detected in a blood sample from a patient who was sickened during a recent outbreak of yellow fever in the southern country of Angola.

The case raises questions about the risk of Japanese encephalitis circulating in Africa and causing further human infections, Etienne Simon-Loriere, PhD, from the Pasteur Institute in Paris, and colleagues said.

“Importantly, it is impossible to differentiate [Japanese encephalitis] from other causes of encephalitis without a specific test. If this is not an isolated case, the existence of a vaccine would make it possible to implement public health measures,” Simon-Loriere told Infectious Disease News.

According to the CDC, Japanese encephalitis is the leading cause of preventable encephalitis in Asia and the Western Pacific. There are multiple available vaccines for the virus, including one approved since 2009 for travelers from the United States to countries where it is endemic. The severe form of the disease causes death in up to 30% of cases.

Although local transmission of the virus had never been documented in Africa, Simon-Loriere and colleagues said the presence in Angola of suitable mosquito vectors — namely, the Culex tritaeniorhynchus species — and animal hosts such as pigs means more surveillance is needed.

“Increased levels of population movement between Asia and Africa may provide opportunities for pathogens to expand their geographic range,” they wrote.

The Angola patient, a man aged 19 years, was admitted to a hospital in March 2016 with symptoms that included fever, headache and jaundice. He lived in the capital city of Luanda, where the Angolan yellow fever outbreak began in December 2015, and had not traveled abroad.

According to the letter, the man’s blood tested positive for a yellow fever variant related to both the 1971 yellow fever outbreak in Angola and a sample taken recently from a Chinese traveler returning from Angola. Simon-Loriere and colleagues expressed surprise that high-throughput RNA sequencing done in Paris also uncovered a Japanese encephalitis genome related to variants from Asia.

They said sample contamination is unlikely because labs in Senegal and Paris where the RNA was handled never had any material containing Japanese encephalitis. Further, no other samples from patients with yellow fever treated at the same time had evidence of the virus.

Simon-Loriere and colleagues said the finding further demonstrated that high-throughput sequencing — particularly untargeted approaches — can be useful for pathogen surveillance.

“It is a way to detect unexpected pathogens or divergent versions of a known pathogen instead of testing a large panel,” Simon-Loriere said. “Once a pathogen is identified, it is of course much more efficient in cost and time and to use targeted approaches.” – by Gerard Gallagher

Reference:

Simon-Loriere E, et al. N Engl J Med. 2017;doi:10.1056/NEJMc1701600.

Disclosure: Simone-Loriere reports no relevant financial disclosures. Please see the full letter for a list of all other authors’ relevant financial disclosures.