Author(s): Trevor Shoemaker, Mary Joung Choi

Infectious Agent

Enveloped, single-stranded RNA viruses in the genus Henipavirus, family Paramyxovirus can infect humans. Of the 6 identified Henipavirus species, Hendra virus and Nipah virus are highly virulent emerging pathogens that cause outbreaks in humans and are associated with high case-fatality ratios. In August 2022, a new Henipavirus species (Langya virus, LayV) was identified among febrile human cases in eastern China. Phylogenetic analysis of Langya shows it to be most closely related to Mojiang virus. Mojiang virus, along with two other Henipavirus species—Cedar virus and Ghanaian bat virus—are not known to cause human disease.

Transmission

Pteropid fruit bats (flying foxes) are Henipavirus reservoir hosts. Hendra virus is transmitted to humans through direct contact with infected horses or body fluids or tissues of infected horses; horses are infected through exposure to bat urine. Hendra virus is not transmitted person-to-person or directly from bats to humans.

Nipah virus is transmitted through contact with infected pigs or bats; consumption of date palm sap or fallen fruit contaminated with bat excretions is another route of exposure. Person-to-person transmission of Nipah virus has been reported through close contact with infected people, including respiratory droplets. Nipah transmission is facilitated by cultural and health care practices in which friends and family members care for ill patients.

Initial sampling of small wild mammals detected Langya virus predominantly in shrews (71 of 262 [26%] sampled) belonging to the species Crocidura lasiura and Crocidura shantungensis. More research is needed to definitively determine the natural animal reservoir(s), susceptible species, and routes of transmission to humans. Preliminary evidence is not suggestive of person-to-person transmission of Langya virus.

Epidemiology

To date, no Henipavirus infections have been reported among travelers. Hendra virus outbreaks in Australia are caused by exposure to sick or dead infected horses. Since 1994, Hendra virus has been reported nearly annually in the eastern states of Australia. Nipah virus outbreaks in humans were reported in 1999 in Malaysia and Singapore and are reported almost annually in Bangladesh and India, typically resulting from direct or indirect bat exposure, but also less commonly through person-to-person spread or exposure to sick or dead pigs. Pteropid bats can be found throughout the tropics and subtropics, however, and henipaviruses have been isolated from these animals in East Africa, Central and South America, Asia, and Oceania.

As of August 2022, researchers have identified a total of 35 non-fatal human cases of Langya virus infection. Further research is needed to determine the geographic distribution of this newly identified virus.

Clinical Presentation

Incubation period is ≈5–16 days (and rarely ≤2 months). Both Hendra and Nipah virus infections can cause a severe influenza-like illness with dizziness, headache, fever, and myalgias. The disease can progress to severe encephalitis with confusion, abnormal reflexes, seizures, and coma; respiratory symptoms also might be present. Relapsing or late-onset encephalitis can occur months or years after acute illness. The case-fatality ratio of Hendra virus is 57%; among 7 known human cases, 4 were fatal. Case-fatality ratios for Nipah virus infection are 40%–70% but have been 100% in some human outbreaks.

Most of the 35 known cases of Langya virus infection have reported non-specific clinical symptoms (e.g., anorexia, cough, fatigue, fever, headache, myalgia, nausea, vomiting). No deaths due to Langya virus have yet been identified.

Diagnosis

Laboratory diagnosis is made by using a combination of tests, including ELISA of serum or cerebrospinal fluid (CSF); reverse transcription PCR of serum, CSF, or throat swabs; and virus isolation from CSF or throat swabs. The Centers for Disease Control and Prevention (CDC) can test specimens from patients suspected to be infected with a Henipavirus. Prior to submitting specimens to CDC, contact the state or local health department to arrange a clinical consultation, or call the CDC Emergency Operations Center at 770-488-7100.

Treatment

No specific antiviral treatment is available for Henipavirus infections. Therapy consists of supportive care and management of complications. Ribavirin has shown in vitro effectiveness, but its clinical usefulness is unknown. A monoclonal serotherapy has been proposed for Hendra in Australia.

Prevention

Travelers should avoid contact with bats, sick horses and pigs, and their excretions. Travelers should not consume fallen fruit, raw date palm sap, or products made from raw sap. A Hendra virus vaccine for horses has been licensed in Australia and has potential future benefit to prevent Henipavirus infections in humans, but no licensed vaccines for humans currently are available.

CDC websites: Hendra virus disease; Nipah virus