CASE NOTES


Outbreak of henipavirus in the southern Philippines, 2014

Debbie Eagles, CSIRO Australian Animal Health Laboratory (CSIRO AAHL) 

Note, this work has previously been:

The paper is adapted from the Epizone conference abstract.

Posted Flock & Herd March 2016

Objective

This paper describes the investigation of an outbreak of neurological disease with high case fatality amongst people and horses in southern Philippines in 2014. Clinical case presentation, epidemiologic findings and laboratory results suggest that the causative virus was a henipavirus, most likely Nipah virus or a virus closely related to Nipah antigenically and genetically. The outbreak occurred in an area where consumption of horsemeat is customary, and there appeared to be a strong epidemiological link between involvement in the slaughter of horses and human illness.

Methods

From March-May 2014, in two small villages in Sultan Kudarat province in the southern Philippines, at least 11 people suffered acute encephalitis and 9 horses developed neurological signs. Post-outbreak investigation by a joint World Health Organisation and Philippines Department of Health team included interviews of villagers and collection of sera from convalescent human cases and in-contact individuals and animals. These samples and the limited number of clinical human samples available were tested for a range of possible aetological agents. Both agent detection and serological assays were used. As all horses had been consumed, no clinical samples from this species were available for testing.

Results

Eleven cases of acute encephalitis in people were considered to be outbreak related. Of these, 9 individuals died. Additionally, 5 cases of severe influenza-like illness (ILI) and one with meningitis were also thought to be outbreak related. All nine affected horses were either found dead or were slaughtered after acute onset, rapidly progressive neurological disease including ataxia, circling and head pressing. 

Epidemiological investigation showed a strong link between clinical disease in people and involvement of those individuals in the slaughter of horses and/or the handling of raw horse meat for preparation for consumption. However, for at least 5 cases, clinical and epidemiologic evidence suggested direct human-to-human virus transmission. No protective equipment was used by those who cared for case-patients in the home, and health care workers used gloves and a face mask but not eye protection.

Human samples were tested for a range of neurological aetiologic agents, and were negative for all but henipaviruses. Three recovering individuals (two recovering from encephalitis and one from ILI) had antibodies to Nipah virus in a range of serological assays. Some of the same sera also tested positive to Hendra virus, but to significantly lower titres than to Nipah virus. Only one sample, a serum sample from an individual that subsequently developed Nipah antibodies, tested positive to Nipah virus in a real-time PCR assay. Laboratory testing was limited by the small number of samples available from clinical cases and sample degradation due to the remote area of the outbreak and consequent lack of appropriate storage facilities. No virus could be isolated from any samples and no significant sequence data could be obtained.

Subsequent testing of sera from a range of bat species showed antibodies to Nipah virus in Pteropus vampyrus bats sampled near the outbreak region.

Discussion

Based on case presentation, epidemiologic findings and laboratory results the outbreak was attributed to a henipavirus. The causative virus was either Nipah virus or a virus that is antigenically and genetically closely related to it.

Epidemiologic data suggest that the most common route of virus transmission to humans was through contact with contaminated body fluids during slaughter of sick horses, and/or handling of raw meat from infected horses. The evidence of human-to-human transmission in this outbreak confirms the need for preventative measures in home care and health care settings.  As with all henipaviruses, it is expected that the reservoir host is a flying fox. Preliminary serological testing confirms the presence of antibodies in at least one species of flying fox within the area.

Rapid response to new outbreaks, collection of appropriate samples for further characterization of the virus and investigation of risk factors associated with spillover and virus transmission are all required for prevention of future outbreaks.

 


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