Kerala is going through the second outbreak of Nipah virus in two years. The first episode occurred in Calicut and resulted in the death of 17 out of 19 people who got the infection. A deadly virus that has high case fatality rate and no proven curative treatment, Nipah is a subject that needs the attention of healthcare professionals and general public alike.
There is no approved preventive medicine or vaccine available at this time. Therefore, detecting cases early and preventing the spread of virus are matters of great priority. This article describes the fascinating science behind Nipah virus infection, with emphasis on practical methods to reduce the spread of disease in the community.
Why is Nipah a serious problem?
Even though the total number of deaths from Nipah virus infection is small when compared to other conditions such as cancer, heart disease, suicides and accidents, Nipah outbreaks affect the social, emotional and economic health of large sections of healthy and productive people.
Panic and misunderstanding among the general public during the Calicut outbreak of 2018 resulted in people staying inside their homes and away from work, shops, other businesses and public transport for several weeks—on an unprecedented scale. Indirectly, this affected the livelihood of many, and dented the economy of the country. Out of irrational fear, hospitals and clinics in the Calicut area were shunned by patients. This meant that suffering from other ailments got worse—an unforeseen adverse outcome of the Nipah outbreak.
Exactly a year later, another outbreak has now been reported at Ernakulam.
What is the role of the bat in Nipah virus infection?
The natural reservoir of the Nipah virus is the fruit bat. Not all bats carry the virus. However, when present, the virus lives peacefully in the bat’s body— apparently without causing disease. Nipah virus can be detected in the bat’s saliva, urine and reproductive fluids. When the virus incidentally enters the human body, it causes illness. Hence, in the life cycle of the Nipah virus, humans are called the incidental host. The Nipah virus can cause human infection either directly from a bat or after living temporarily in another animal such as the pig, also called the amplifier host.
In the Malaysian outbreak, pigs that ate fruit fallen on the ground and contaminated with bat saliva, served as the amplifier host. Infected pigs developed cough, and passed on the virus to those who worked on the pig farm. Other mammals have also been occasionally identified as hosts.
The passage of the Nipah virus directly from bats into humans is believed to be a rare occurrence, and is referred to as ‘spill-over case’. In Bangladesh, 79 such spill-over cases have been documented from 2001 to 2014. The exact mechanism by which the virus transfers from the bat to humans is not clear, and there are several theories about how this might occur.
In Bangladesh, it is speculated that consumption of raw date palm sap could have resulted in this transfer. The reasoning here is that fruit bats regularly visit the date palm at night. As a result, its saliva and urine are found in the pot kept on the tree to collect the sap. This creates a potential pathway for the Nipah virus to infect humans who consume the liquor. However, it should be noted that raw date palm sap, also called tari, is regularly consumed by hundreds of thousands of people, whereas only very few have come down with the disease.
Bat-human interactions occur in other ways too. Bats are consumed as meat in certain communities. Overhead electric lines kill a substantial number of bats. Bats get inadvertently trapped and die when fishing nets are used to cover fruit trees by farmers. Handling a dead bat with bare hands can be potentially dangerous if that bat was a host for the Nipah virus. Men climbing fruit trees frequented by bats get exposed to bat droppings, urine and saliva sticking to the leaves and branches. Bat droppings--known as guano—are used as fertiliser. However, the role of these interactions in the transmission of Nipah virus to man is uncertain.
In the Kerala outbreak of 2018, even though the first reported cases were originally linked to a local well that was infested with bats, it was found that the bats were of a different variety, and could not have been the source of infection.
Considering the enormous size of the bat population, their importance to the ecosystem, the health risks of handling bat carcasses, and how infrequently Nipah virus is present in them, attempting to control bats is not a worthwhile strategy at this time. Minimising interaction with bats, however is a sensible thing to do.
How can we prevent Nipah virus in the wild from infecting humans again?
Although human-to-human transmission is well-documented, the original source of the Nipah virus infecting patients in Kerala unfortunately still remains a mystery. Therefore, concrete recommendations cannot be made about preventing another outbreak.
One of the prevention strategies employed in Bangladesh was to discourage consumption of tari, the raw date palm sap. Strategies to keep bats away from the tapping apparatus are also being employed. By the same token, there is speculation that toddy from coconut trees could also be contaminated by bat’s secretions. Some experts therefore suggest avoiding toddy collected in open pots, particularly in areas infested with bats.
While visiting trees, infected fruit bats could leave traces of the virus along with their saliva as they bite on ripe fruits. Some of these fruits drop on the ground, and the bat moves on in search of other fruit. Although it is questionable whether such a low dose of the virus can actually cause infection in man, it is generally recommended to avoid eating fruit that is found on the ground underneath a tree. Fruit purchased from the market is safe, but should be washed thoroughly as always before consumption.
What are the best strategies against Nipah and why?
From a public health standpoint, it is well-established that most of the Nipah-related deaths in Bangladesh and India occurred following human-to-human transmission: that is when the virus spreads to other people from the first patient.
Clearly, this is the area where our efforts must be concentrated on. A significant part of such work involves building awareness as well as dispelling myths and fake messages that cause panic in the community.
How to reduce human-to-human transmission?
Transmission of infection occurs when the virus enters the body of people who happen to be in close contact with the patient. In decreasing order of severity, from a learning standpoint, there are three important categories of human-to-human transmission.
In the first category are close family members. Studies from Bangladesh confirmed that wives of patients were the worst affected. This is because in most instances, wives were the primary care-givers and were exposed to the patient’s body fluids over long periods of time. Those who took care of the patient after death are also at high risk.
The second category includes healthcare workers, especially those who are exposed to the patient’s body fluids. The death of a nurse in Calicut is a case in point, and illustrates the need for healthcare workers to protect themselves by using universal precautions as well as specific personal protective equipment (PPE) while dealing with patients who could possibly be having Nipah virus infection.
The third category comprises the casual contacts of the patient. These are people who incidentally become contacts, by virtue of sharing time and space with the patient just before or soon after the diagnosis of Nipah virus infection was made.
The importance of tracking contacts.
One of the biggest challenges in an outbreak like Nipah is to correctly track down and quarantine the contacts of the patient. Those who had close physical contact or exposure to body fluids of the patient is considered a contact. In addition, for classification purposes, anyone who spent 15 minutes or more with a patient is also considered a contact. Such a person could be a co-passenger in a car ride, a hostel roommate, a nurse or doctor who attends the patient, a patient who shares the hospital room, a lab technician who draws blood or a radiographer who takes an X-ray.
Contacts may or may not harbour the virus, but need to be quarantined at home and carefully monitored over at least 3 weeks for manifestations of disease. The reason for quarantine is that contacts who have the virus might initially feel well, and inadvertently pass the virus on to those around them if they went about their daily routine. During the quarantine period, if any of the contacts develop symptoms, they need to be admitted to a designated isolation facility.
Obviously it is cumbersome and expensive to isolate, quarantine and observe large numbers of people. To quote an example, the single Nipah case in Ernakulam has generated 327 contacts so far, all of whom required observation to varying degrees according to protocol. Although none of them have so far been found positive for Nipah, it is obvious that the lower the number of contacts, the better it is for everyone.
How fast can Nipah spread between people?
Contrary to common belief, Nipah viruses do not travel long distances through the air to infect large numbers of people. Neither does it get transmitted to people who casually or briefly interact with the patient—that is without physical contact. Its risk of spread (basic reproduction number R-0) is only 0.33-0.48, which is small compared to 10-12 for other common viral and bacterial contagious illnesses.
The risk is of spread is greater when there is physical contact with the patient, particularly with body fluid exposure. While interacting with the patient from close quarters, or while handling material contaminated with the patient’s body fluids without gloves, the virus can spread to other people by sticking to their hands. Such infected material could be the patient’s clothes, used masks, cutlery, glasses, mobile phone or even a pen. Frequent handwashing is an effective preventive strategy.
Those patients with cough and breathing difficulty spread more virus. It is worth noting that each cough sends out thousands of tiny droplets from the lungs and throat of the patient, at speeds than can exceed 80 kmph. Especially at risk are those within arms’ length. Hence, during an outbreak, a useful rule of thumb is to keep a distance of at least 1 metre from anyone who has a fever.
What is cough etiquette?
Cough etiquette is an important method of reducing the spread of all airborne germs.
Cough droplets from the patient enter the lungs and stick to the skin of other people, particularly those who are within about one metre distance from the patient. Diseases ranging from the common cold to tuberculosis and Nipah virus spread by coughing.
People should not cough at their palms—this is an easy way to spread viruses to other people by shaking hands afterwards.
Those with a fever must be taught to cover their mouth with a cloth or tissue while coughing or sneezing, or to turn their head sideways and cough at their partly bent elbow. The rationale here is that unlike fingers on our hand, the elbow is not a body part that is used to touch and thereby infect other people. Frequent hand sanitisation is to be practised by patients, bystanders, and healthcare workers.
To the extent possible, those who are actively coughing or sneezing should avoid being in public places until their symptoms are better.
The concept of fever clinic.
Used during the Calicut Nipah outbreak of 2018 as a containment tactic, a fever clinic is basically a section of the hospital that is earmarked for exclusive treatment of those with fever, and to identify potential cases of Nipah.
Although only one patient has been identified so far in Ernakulam, there could be other Nipah patients in the community who will come to the hospital in the near future when symptoms appear. The typical incubation period is 4-14 days, which means that symptoms are expected to appear within two weeks in most cases. Obviously, most patients with fever who visit the hospital will not have Nipah. But all Nipah patients will have fever, hence the focus on fever patients.
On a regular working day at any hospital, patients go to several parts of the facility for various purposes. However, with the introduction of fever clinic, as all those with fever are directed to a single location, fewer staff members get exposed to the virus. Hospital personnel assigned to this area can wear protective equipment against the virus.
Thus, one of the basic aims of the fever clinic is to reduce the number of people who get exposed (and thereby become contacts) when such a patient comes to hospital.
Fever clinic must be manned by staff wearing N95 masks, gloves and other equipment. This applies to all staff and doctors who are within 1 metre distance of a patient. Ordinary surgical masks are not protective against the virus. However, they can be used by people with cough so that droplet spread is less.
At the fever clinic, patients get screened for symptoms that suggest Nipah virus infection. Those whose symptoms match are promptly sent to the local referral centre for expert evaluation. Collection of samples is not required at the fever clinic for suspected Nipah cases. It will be done at the referral centre.
Those fever patients whose symptoms do not match the Nipah criteria are treated as usual at the hospital or clinic. This protocol continues until the outbreak is officially declared over.
What are the symptoms of Nipah virus infection?
Most cases of fever are not from Nipah virus infection. However, among those who live in the locality of Nipah outbreak, if someone develops fever along with other symptoms such as severe headache, cough, breathing difficulty or disorientation, they must be evaluated for possible Nipah infection.
In summary, Nipah virus outbreak management requires the concerted work of healthcare professionals, scientists, hospitals, government machinery, media and general public. Although the virus is deadly and contagious with no cure in sight, it can still be defeated by early identification of the outbreak and initiation of quarantine measures. Building awareness among the general public as well as those employed in the field of healthcare about universal safety precautions is crucial to reduce the impact of all infectious diseases.
Nipah Virus infection Guidelines: Directorate of Health Services, Kerala
Nipah virus experience from Bangladesh
Nipah virus experience from India
Detection on Nipah in the fruit bat
WHO article on emerging zoonoses
Nipah virus infection patterns in Bangladesh https://www.ncbi.nlm.nih.gov/books/NBK114486/
The presence of Nipah virus in bats
Nipah virus infection
Universal precautions in healthcare