U of T Expert on the Rise of Zoonotic Infections

Zoonotic infections like Nipah virus and Ebola have begun to appear more rapidly among human populations over the past twenty years, but experts have yet to conclude why this may be the case. The lesser-known Nipah virus has been part of a recurrent outbreak in India since the late 1990’s, where it has a high-case fatality rate of 40-60%.

“Nipah virus is different from Ebola in that it more readily affects the lungs and the brain,” said Dr. Sharmistha Mishra an assistant professor at the Institute of Health Policy, Management and Evaluation, and an infectious disease physician and epidemiologist at St. Michael’s Hospital. “While Ebola attacks the organs and shuts down the body in large part due to fluid loss, Nipah can have severe neurological side effects that vary depending on how the body reacts to the virus.”

Treatment of those infected with Nipah requires intensive supportive care, but symptoms can also appear on a spectrum of severity. Some people develop only flu-like symptoms, while others can suffer seizures or end up in a comatose state.

“There is no vaccine as yet, though investigational agents are being considered,” said Mishra who is also a clinician scientist at the La Ka Shing Knowledge Institute.

The unassuming date palm fruit is the likely point of animal to human transmission of the virus in the case of the most recent outbreaks. In the country of Bangladesh, which has seen a yearly outbreak of the disease since the late 90’s, the virus was transmitted to humans from consumption of raw date palm syrup or the date fruit, which can be contaminated by the saliva or urine of the fruit bat.

“The fruit bat is the animal reservoir for this particular virus, and the reason why these types of infections are known as zoonotic,” said Mishra.

According to the World Health Organization, the Nipah virus is also considered to be an emerging zoonosis. Infectious disease epidemiologists are still learning about how these viruses move from animal to human, but the growing trend seems to imply that more of these outbreaks are likely to occur in the future. Humans and wildlife are coming into closer and closer contact, through farming or abattoirs, and in the case of Nipah, human encroachment on forest territory could be another factor in the virus’ spread.

The first outbreak of Nipah occurred in Malaysia before it spilled into Singapore in 1998.

“It spread from bats to pigs that were being farmed and from pigs to their human farmers,” said Mishra.

The virus has since continued to resurface, often in India and surrounding regions like Bangladesh. Following a 2004 outbreak in the country, researchers worked to find out more about how the virus was spread from human-to-human.

“Person to person transmission in the case of Nipah is largely through respiratory secretions, like saliva and sputum (phlegm) but is usually contained to those who are caring for individuals already sick with the virus,” said Mishra. She adds that there is currently no suggestion that the virus is spreading from human to human across states in India.

However, the recent outbreak of Nipah virus highlights the importance of the need for continued field epidemiology and case investigations of zoonotic infections, as well as the strengthening of front-line healthcare facilities in early detection of cases, and in infection prevention and control.

“We need to figure out what happened to the virus in the bats, we don’t yet know if it is another strain, and there is much to also learn about animal to human and human to human transmission” said Mishra. “The things we learned from John Snow and his work on the cholera virus in investigating outbreaks, continues to be a massive part of what we do now in the field.”

Further, baseline strengthening of a country’s health care system is also key to controlling zoonotic outbreaks and preventing further human-to-human transmissions. According to Mishra, India has more than enough expertise in this area. During the Ebola crisis, team members from the National Centre for Disease Control in India  as well as members of various medical colleges, came to West Africa to provide epidemiological support.

An additional challenge that remains is communicating and working with the local panchayats or village councils to create awareness and address the fears and stigmas that can undermine rapid response control efforts.  “There is still a lot of stigma attached to these kinds of viruses, and in outbreaks of this nature, making individuals fearful of going to health care facilities, especially when healthcare workers become infected,” said Mishra.

Infection prevention and control, health promotion, clinical research, and a refined field and molecular epidemiological approach that combines the study of wildlife and human behaviors, are all key to understanding how zoonotic infections spread in populations and cause disease in our bodies. Along with the support of the World Health Organization, these methods will hopefully allow us to prevent and reduce their potency in the years ahead.