Excerpt from Hunter’s Tropical Medicine and Emerging Infectious Diseases E-Book

Paramyxoviruses (Nipah, Hendra, Menangle)

There is phylogenetic evidence that bat paramyxoviruses were ancestors to all major extant paramyxoviruses, including measles, mumps, parainfluenza, respiratory syncytial virus, and important veterinary pathogens. Three emerging paramyxovirus infections have been described for which bats are the likely natural reservoirs, and domestic horses and pigs have proved to be the amplifying vectors for human infection. Hendra and Nipah viruses are Henipaviruses; Menangle is a Rubulavirus.

Hendra Virus

In 1994, there was an outbreak of fatal respiratory disease in horses and humans in Australia, attributed to a new pathogen, Hendra virus, whose natural reservoir is Pteropus spp. (P. alecto, P. poliocephalus, P. scapulatus, P. conspicillatus). Since 1994, there have been 60 outbreaks of Hendra in the northeastern coastal region of Australia, causing the deaths of 102 horses and four of seven human cases, including two veterinarians.

Nipah Virus

In 1998, there was an epidemic of encephalitis in Malaysia and Singapore affecting pigs and pig handlers in whom the case fatality was more than 40%. The causative virus, named Nipah after an affected village, is closely related to Hendra virus. Pteropus vampyrus and Pteropus hypomelanus are the natural reservoirs. In 2001 a geographically distinct strain of Nipah virus emerged in West Bengal and Bangladesh, causing respiratory as well as encephalitic symptoms, with subsequent annual outbreaks and case fatality of more than 74%. Transmission in the original Malaysia/Singapore epidemic was via infected pigs, whereas in India and Bangladesh it was by drinking infected date palm sap or by human-to-human contact. In 2018 there was a Nipah virus (Bangladesh lineage) epidemic in Kozhikode and Malappuram districts of Kerala, South India. There were 23 cases with a 91% case fatality rate. Apart from the index case, who was probably infected by a pet Pteropus giganteus, transmission was nosocomial, probably through aerosol spread by coughing. So far, more than 600 human cases of Nipah virus encephalitis have been diagnosed. The epidemics have been attributed to disruption of Pteropus ecology by deforestation (e.g., building the new Kuala Lumpur airport), which displaced the bats from their traditional roosts to agricultural areas where they have contact with domestic animals and humans. In Bangladesh and India, where there have been >150 deaths, human-to-human transmission within families has been inferred.

Menangle and Tioman viruses have been isolated from Pteropus spp. in Australia and Malaysia and from sick pigs. Influenza-like illness in pig farmers with Menangle seroconversion has been reported.