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27 Apr 2017

First case of Japanese encephalitis in Africa

Researchers from the Institut Pasteur in Paris and the Institut Pasteur in Dakar (Senegal) have detected a co-infection by the Japanese encephalitis virus (JEV) and the Yellow fever virus (YFV) in a patient in Angola. This concerning news raises the issue of the risk of circulation of JEV in Africa, when it is known to be endemic to Asia and Western Pacific. The detection was the subject of a correspondence in The New England Journal of Medicine, on 13 April 2017.

In March 2016, a yellow fever outbreak affected Angola and the Democratic Republic of the Congo. The total number of confirmed cases reached 965 across the two countries, with thousands more cases suspected (WHO). Later on, researchers from the Institut Pasteur in Dakar and the Institut Pasteur in Paris, working in collaboration with colleagues at WHO obtained a sample from an Angolan patient (who had not traveled abroad) to process high-throughput RNA sequencing (RNA extraction in Dakar and construction of libraries and sequencing in Paris). Because the protocol uses « randomly primed cDNA synthesis, it provides a comprehensive and quantitative view of all RNA present in the sample and enables the characterisation of potential connecting viruses ». The scientists were surprised by the sequencing result: in addition to the expected YFV genome, they also found a JEV genome, not likely to be due to contamination.

Transmitted by different species of mosquitoes, YFV and JEV both belong to the family of Flaviviridae (a family also including Dengue and Zika viruses among others). They also circulate in disjunct geographic areas: while YFV is found  in tropical areas of Africa and South America, JEV was till now only found in Asia and Western Pacific. The detection of such a co-infection raises the issue of the risk of circulation of JEV in Africa. Even if this autochtonous infection by JEV could only be an isolated case, the presence of competent mosquitoes in Angola, as well as other animal hosts (swine or waterfowl) could still allow the virus to circulate more durably.

Geographical distribution of risk areas for YFV and JEV (© Institut Pasteur)

This work demonstrates the importance of seroepidemiological investigations to estimate the proportion of the Angolan population that has been exposed to JEV. Such studies would enable an assessment of the need for implementing disease control measures, specifically vaccination campaigns as an efficient vaccine is available. It also demonstrates the relevance of random high-throughput screening technique for pathogens surveillance. The Institut Pasteur and its International Network (IPIN) fully adhere to this technological effort.

Increased global population movements, notably between Asia and Africa, are a factor facilitating the spread of infectious diseases. Recently, there has been imported cases of Yellow fever or Rift Valley Fever in China.

The publication:

Autochthonous Japanese Encephalitis with Yellow Fever Coinfection in Africa, N Engl J Med 2017; 376:1483-1485, April 13, 2017, DOI: 10.1056/NEJMc1701600

Simon-Loriere E, Faye O, Prot M, Casademont I, Fall G, Fernandez-Garcia MD, Diagne MM, Kipela JM, Fall IS, Holmes EC, Sakuntabhai A, Sall AA.

Source:

Institut Pasteur, press release, 14 April 2017 (in French)