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The possibility of zoonotic infections causing pandemics has been a concern for decades. Nipah virus (NiV), Hendra virus (HeV), and Rift Valley fever virus (RVFV) are all zoonotic infections that can cause encephalitis in humans, sometimes fatally. In this chapter we will discuss these viruses and their effects on humans along with proper infection control measures.
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Epidemiology and Risk Factors
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The Nipah virus (NiV) causes a zoonotic infection which was first described in Sungai Nipah village in Malaysia in 19981 (Figure 26-1). Nipah virus is an enveloped single stranded RNA virus and is a part of the Henipavirus genus and Paramyxoviridae family. The virus ranges from 120 to 500 nm in diameter. The first outbreak occurred in Malaysia in 1999. NiV and HeV have only minor ultrastructural differences and have significant cross reactivity on serological tests.2,3
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Both NiV and HeV are transmitted by specific fruit bats known as flying foxes, from the Pteropus genus. Flying foxes are endemic to Asia, China, Australia, some parts of Africa and the Pacific islands.4 Infected bats shed NiV and HeV in their saliva, urine, semen, and excreta but are asymptomatic carriers. Infection in humans occurs through contact with flying fox urine, saliva, secretions or an intermediate host like pigs through contact with sick animals or animal products.4
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Outbreaks of NiV have occurred in humans in Malaysia, Singapore, Bangladesh, India, and the Philippines. Outbreaks in Bangladesh and India appear to happen on an almost annual basis. The outbreaks in Malaysia and Singapore were thought to be through direct contact with NiV-infected pigs and their products. In the Malaysian and Singaporean outbreaks 92% of infections were associated with pigs. Pigs likely become infected through ingestion of food contaminated by flying fox secretions. Dogs were also found to be infected during the Malaysian and Singaporean outbreaks and dogs dying on farms was found to be another risk factor.5 Control of the outbreak led to culling over a million pigs followed by its disposal by deep burial and decontamination with quick lime, use of protective equipment when handling contaminated animal products, and banning animal trade during the outbreak.2 Person-to-person transmission was not proven experimentally in the outbreaks in Malaysia or Singapore.
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In the Bangladesh’s and India’s outbreaks there was no clear evidence of infection via pigs and it appeared that the outbreaks were seasonal.2 Infections likely occurred through consumption of raw date palm sap or consumption of fruits contaminated by flying fox secretions. The outbreaks seemed to coincide with the sap harvesting (December–May).6 There was strong evidence of person-to-person transmission found in the ...