Nipah
Nipah virus is an enveloped Paramyxovirus with a non-segmented ribonucleic acid (RNA) genome. The first outbreak of Nipah virus occurred in the Malaysian village called “Sungai nipah” in 1998-1999. Subsequently outbreaks have been recorded from Bangladesh and the neighbouring West Bengal in India. Since 2018 Kerala has seen recurrent outbreaks of Nipah infections. And the virus seems to be adapting. Until recently, two distinct strains of the Nipah virus were identified by genetic analysis – the Nipah virus Malaysian variant (NiVM) and the Nipah virus Bangladesh variant (NiVB). They showed significant difference in mortality although about 91.8% homology was present between the genomes. The Malaysian outbreak had about 40% case fatality rate, whereas the the outbreaks due to NiVB had about 75% case fatality. The genoptype 1 that has been detected in the current outbreak in Kerala in 2023 bears similarity to the Bangladesh variant.
The reproduction number (R0) of the Nipah virus infection from the Bangladesh outbreaks was estimated to be 0.48, but this increased with advancing age. In a study of 23 Nipah virus spill overs, those with respiratory symptoms and those who died were more likely to transmit the virus. In the Kerala outbreaks since 2018, respiratory symptoms have been predominant among affected individuals which could potentially cause large areas to be affected had it not been for the prompt containment measures from the administrative authorities. Nevertheless, the transmissibility of the infection in the previous outbreaks in Kerala has not yet been systematically understood.
Nipah virus has been classified as a biosafety level 4 pathogen. Therefore it requires laboratories equipped with biosafety cabinets with controlled airflow, filtered ventilation systems, special attire for the laboratory staff and equipment to decontaminate the waste, in addition to the laboratory having to occupy a safe isolated zone in a large building or be in a separate building. In clinical practice, personal protective equipments including N95 masks, gloves, coveralls and safety goggles have been utilised to take care of Nipah infected patients. All these pose huge logistical challenges and hamper patient care. These practices need to be re-evaluated scientifically as new viral strains develop and new evidences emerge.
It’s time we moved beyond lockdowns and quarantining of contacts. About 8% of infections in the Malaysian Nipah outbreak were asymptomatic. But in the Bangladesh outbreaks no asymptomatic infections were found. Sero-surveillance of those possibly “endemic” regions is needed and vaccines need to be developed. We have highly effective vaccines against some of the other Paramyxoviruses, for example, the Measles and Mumps viruses. More important for the treating clinician is developing an effective antiviral treatment. Although animal studies and observational data for a few antivirals are available in the literature, a clear guidance backed by robust data is yet to be conceived.
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