Should Kerala expect a Nipah outbreak every year?
Possibly yes, say infectious disease experts.
The health system would have to prime itself for developing a quick response system and standard infection control protocols for all hospitals as recurrent outbreaks of Nipah — and not necessarily in the same location or with the same symptomatic profile — could be a real possibility in Kerala, says G. Arunkumar, Director, Manipal Institute of Virology, who led the epidemiological investigation into Kerala’s first-ever Nipah outbreak in 2018.
During the Kozhikode outbreak, fruit bats (Pteropus bats/flying fox) were established as the key reservoirs of NiV by the National Institute of Virology, Pune/Indian Council of Medical Research, with 19.2% (10/52) of the bat samples testing positive for the same virus strain that had been isolated in human samples.
Subsequent outbreaks
“Wherever Nipah has been reported in South East Asian nations, there have been outbreaks in subsequent years. The fact that fruit bats are commonly found across the State and that 20 % of the bat samples from one site had tested positive for NiV (Nipah virus) means that we stand the risk of fresh annual outbreaks anywhere in the State,” says R. Aravind, Head of Infectious Diseases, Government Medical College Hospital, Thiruvananthapuram.
The outbreaks usually coincide with the breeding season of bats, during December-May, when the virus replicates in bats.
In Kozhikode, only the index case had contracted the infection directly from the bats while the rest were all human-to-human transmission cases.
“Priority should be in ensuring that no human-to-human transmission occurs in hospital settings,” Dr. Arunkumar says.
Also, every infected human case is not necessarily a “super transmitter”. In Kozhikode, 19 persons got the infection from the index case, primarily because Acute Respiratory Distress Syndrome (ARDS) was the major symptom. NiV transmission occurs by droplet infection and all 19 persons caught the infection because the index case had been coughing continuously and had vomited too.
May not be severe
The lone confirmed Nipah case in Kochi however, seems to have developed encephalitis and apparently, lung involvement is less.
Also, the duration of his symptoms developing into encephalitis has also been long, indicating that the infection may not be too severe, he says.
It is also possible that this is an isolated case of Nipah, Dr. Arunkumar says. Because Nipah transmission usually takes place towards the last phase of illness when the patient is extremely sick.