Saturday , 20 April 2019

Bats, Fruits and Deadly Viruses

Nandkumar Kamat


Due to lack of immediate detection facilities thousands of deaths in Goa due to viral infections in past could have been classified improperly. So we are not sure whether many deaths due to encephalitis in the past were due to Nipah virus. Goa lacks expertise in proper differential diagnosis of novel viral pathogens or local viral serotypes.

Fruit bats are in news due to Nipah virus first detected in Malaysia in 1998. So far Nipah infections have been reported from Australia, Bangladesh, Cambodia, China, India, Madagascar, PNG, Taiwan and Thailand.  About 15 years ago I noticed fruit bats feasting at night on guava fruits in our garden. In the morning I collected a few ripe, intact guavas which showed their teeth marks. After careful washing and removing the injured portion I consumed the edible pink pulp from just 3-4 fruits and at night came down with vomiting, severe stomach pain, body ache, cramps and it took me three days to recover.

I knew that the illness came from fruit bats, despite washing. We never harvested any fallen fruits and discarded thereafter any edible fruit with bat teeth marks. Even in the market we are careful to exclude ripe tropical fruits except pineapples showing bat teeth marks. Bats are mammals of the Chiroptera order. More than 1100 species of bats are found in world except in polar region. Bats are good pollinators and disperse seeds. Banana, avocados and dates benefit from bat pollination. Bats hunt insect pests of crops at night. Bat excreta is in high demand due to its fertilizer quality. Fruit bats which spread Nipah virus are found in Bhutan, Brunei, China, India, Indonesia, Laos, Madagascar, Myanmar, Nepal, Philippines, PNG, Singapore, Taiwan, Thailand, Vietnam. World’s topmost institution on human pathogens, Centre for disease control in USA (CDC) monitors global spread of the virus borne diseases. After coming in contact with Nipah virus, encephalitis (inflammation of the brain) is noticed after an incubation period of 5 to 14 days.

Symptoms include 3 to 14 days of fever and headache, followed by drowsiness, disorientation and mental confusion. If not detected as Nipah virus, patient can progress to coma within 24 to 48 hours. Some develop respiratory illness, some show severe neurological and pulmonary signs. In 1998-99 infection episode, about 40 per cent of those patients who entered hospitals with serious nervous disease died from the illness. There is neither a vaccine, nor a permanent cure and the long term consequences of infection include persistent convulsions and personality changes. In some cases, the virus can get reactivated and death has also been reported, months and even years after exposure.

Nipah virus-infected pigs transmitted the infection in Malaysia and Singapore outbreak, whereas in Bangladesh and India, Nipah virus infection was linked to consumption of raw date palm sap and contact with bats. This means that in Goa coconut toddy tappers need to be careful, so also people working in cashew plantations visited by fruit bats. Human-to-human transmission has been noticed in infections of Nipah virus in India. Nipah virus is detected at initial stages of diseases by Virus isolation attempts and real time polymerase chain reaction (RT-PCR) from throat and nasal swabs, cerebrospinal fluid, urine, and blood should be performed in the early stages of disease.

Virologists also use Antibody detection by ELISA (IgG and IgM) to confirm identification. There are no medicines for Nipah infection so prevention is only cure. Ribavirin has been effective in laboratory but not tested on humans. CDC advices that “Because Nipah virus encephalitis can be transmitted person-to-person, standard infection control practices and proper barrier nursing techniques are important in preventing hospital-acquired infections (nosocomial transmission). Government of India has shown interest in passive immunisation using a human monoclonal antibody targeting the Nipah G glycoprotein. It has been successfully evaluated in the post-exposure therapy in the ferret model. According to CDC report a subunit vaccine, using the Hendra G protein, produces cross-protective antibodies against HENV and NIPV has been recently used in Australia to protect horses against Hendra virus.

This vaccine offers enormous potential for henipavirus protection in humans as well. Experts believe that “Nipah virus infection can be prevented by avoiding exposure to sick pigs and bats in endemic areas and not drinking raw date palm sap.” Since fruit bats are implicated what can be done in future? We need to have a better understanding of the ecology of bats and Nipah virus. The relation between reproductive cycle of fruit bats and Nipah outbreak need to be investigated.

Government of India needs to equip the state health departments and medical colleges with surveillance tools which should include reliable laboratory assays for early detection of disease in communities and livestock. Community awareness needs to be increased regarding the transmission and symptoms. Government of Goa needs to reinforce standard infection control practices to avoid human-to-human infections in hospital settings (nosocomial infection). Till “all clear” signs are not given people in Goa need to follow the precautionary principles and avoid consumption of fallen fruits, infected fruits, contact with bat excreta in garden and farms and maintain hygiene. Fruit bats are not our enemies. But unfortunately, the lethal viruses are targeting humans through them and in future we shall witness more such novel viral outbreaks. For more information readers may refer to

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