The Kerala state government declared that the Nipah virus outbreak in the Kozhikode and Malappuram districts had ended on 1st July. There were a total of 18 confirmed cases and 17 deaths according to the World Health Organization website, and the last case had been reported on 31 May 2018. There is already a Bollywood-style music video on the end of this outbreak, produced by local Kerala artistes.
The virus naturally infects flying foxes and possibly other species of bats, although it can also infect a large array of other mammalian hosts, including pigs horses, dogs, cats, and of course humans. It is an RNA virus, and belongs to the Paramyxovirus family. It was the inspiration for the pandemic virus (meningoencephalitis virus one – MEV-1) featured in the 2011 movie “Contagion”.
Singapore holds the distinction for being the second country where human cases of Nipah virus infection have been described. The first Nipah virus outbreak started in September 1998 in Peninsular Malaysia, with pigs being the intermediate amplifying host. The outbreak spread to Singapore in February 1999, when 11 abbattoir workers in Singapore were infected via live pigs imported from Nipah-affected areas in Malaysia. The outbreak in Malaysia ended in mid 1999, after the slaughter of close to 1 million pigs from 896 farms in Nipah-affected areas, but not before 105 human deaths from 265 cases were registered. The discovery of this (at the time) novel virus is rightly attributed to Dr Kaw Bing Chua, who was then only a graduate student at the Universti Malaya.
Pork (both frozen pork and live pigs) from Malaysia was banned in Singapore until 2015.
In one sense, however, we were fortunate. There was no secondary transmission of the virus between humans in 1998-1999. In subsequent outbreaks of the virus in Bangladesh and India since 2001, and Mindanao in the Philippines in 2014, a significant proportion of the cases occurred because of human-to-human transmission between infected persons and their close contacts, which included healthcare workers in the hospitals. The Malaysian and Bangladesh/India strains of the Nipah virus differ by no more than 6 nucleotides (the virus in the Mindanao outbreak was never recovered) and are functionally largely indistinguishable. However, these 6 nucleotides somehow resulted in significant differences in terms of the characteristics of human disease, and also perhaps capacity for human-to-human transmission. The Bangladesh/India Nipah virus is associated with greater respiratory tract involvement, higher rates of direct human-to-human transmission, and more deaths when compared to the Malaysian virus. An excellent review from my colleagues in Singapore was just published in April – those who are interested in the clinical and virological details will find them in the article.
New human cases of Nipah virus infection will continue to appear over time because the primary host (flying foxes) is widely distributed and multiple human activities result in contact with them (including making palm wine). Continued vigilance and improving health systems should hopefully limit the impact of each introduction.