All stories have a beginning, even viral infections like the coronavirus pandemic and, more recently, the tragic fatalities caused by the Nipah virus. People died of this infection in Bangladesh and West Bengal and, though separated by 2,300 kilometres, also in Kerala.
Questions arose in people’s minds: “Is it a laboratory-grown bioterrorist weapon? Or is it just a natural tragedy? Has the coronavirus pandemic started again?”
Actually, the story started in 1998 in a village in Malaysia called Nipah, near Kuala Lumpur. Many people mysteriously developed fever, sore throat, breathing difficulty, cough and headache. Some then became drowsy, had convulsions and died.
It was fatal for about 45-60 per cent of the affected people. Those who were lucky enough to develop a milder form of the disease survived. Even among the survivors, who appear to have made a full recovery, approximately one in five people (about 20 per cent) is left with debilitating neurological complications or seizures.
Medical sleuths got to work, ruled out Japanese encephalitis, and found that it was a new disease caused by an old virus that had remained dormant in animals all these years but had now spilled over and attacked the human population. They named it after the village where it was first discovered — the Nipah virus.
Further investigations revealed that the infection was spread by an animal called the “flying fox”. It is not actually a fox that flies but a bat in the family Pteropodidae, which is the natural host of the Nipah virus. The bats that harbour the virus live with it happily and symbiotically, and are totally asymptomatic. These are not blood-sucking vampire bats that infect people by biting them; they are frugivores that feed on figs, mangoes, dates, guavas and bananas. They are particularly fond of date palm sap. This is collected in pots and left to ferment overnight, producing a type of intoxicating country liquor. The bats also enjoy a drink from the pots like their human counterparts but, as they drink and eat, they contaminate the fruit sap and the environment indiscriminately with their saliva and uncontrolled faecal and urinary droppings.
Nobody likes to waste fruit from their gardens or orchards, so even if the fruit appears damaged or bitten, unsuspecting people may eat it or feed it to domestic animals like pigs, cows, dogs and horses.
Infected pigs are highly contagious. They develop severe respiratory disease and a barking cough (“barking pig syndrome”), followed by neurological disease. Mortality is very high in piglets. Close contact with infected pigs, slaughtering them or eating the meat without cooking it properly can cause the disease to spread to humans.
About 75 per cent of horses that contract the virus die. Cows and dogs tend to act as intermediary hosts. They become sick and can spread the disease to their unsuspecting owners but seldom die. All these animals excrete the virus with their saliva, urine and faeces.
The incubation period typically lasts 4-14 days but can extend up to 45 days. During this time, asymptomatic individuals can transmit the disease to others. During an epidemic, contact tracing, frequent handwashing, wearing masks and avoiding potentially contaminated fruit are important. Caregivers and medical personnel are particularly at risk of human-to-human transmission, especially through airborne droplets released during coughing or sneezing. Some (including nurses) have contracted the virus while taking care of infected patients and died.
Diagnosis of Nipah virus infection requires a high degree of suspicion on the part of the healthcare provider. There may be a recent history of travel to an area with an epidemic. During the first few days, RT-PCR (real-time polymerase chain reaction) tests can be done on nasal or throat swabs, cerebrospinal fluid, urine or blood samples. Later, or after recovery, antibodies to the virus can be detected in blood samples using an enzyme-linked immunosorbent assay (Elisa).
The Nipah virus has been detected in several of the world’s most densely populated areas where there is increased proximity and interaction between humans and their environment. Farm animals also live in these crowded areas, increasing the risk of viral spillover between species. Urbanisation, deforestation and population growth have reduced the areas available for animals to live, forcing them closer to humans. Fruit bats need food to survive. As they lose their natural habitats, they will move closer to human settlements, leading to outbreaks of infection and epidemics.