Nipah Virus Encephalitis
Nipah Virus Encephalitis
Nipah virus is best known as the causative agent of a large outbreak of disease among pigs in Malaysia in 1999. It is a member of the Paramyxoviridae family of viruses and is naturally harbored in fruit bats of the Pteropus genus in Malaysia.
The virus may be transmitted to pigs in contact with bat urine or feces and subsequently spread to humans through contact with the pig's bodily fluids on pig farms and in abattoirs (slaughterhouses). In humans, Nipah virus infection presents as encephalitis and respiratory disease and carries a significant mortality rate. Treatment is limited to reducing symptoms, but appropriate preventative measures may be implemented to limit spread.
Nipah virus is considered an emerging infectious disease and is argued to pose a significant potential threat to human health. The impact of this viral infection is evident both economically and socially and the recent evidence of person-to-person transmission raises significant cause for public concern.
Nipah virus was first isolated in 1999 during an outbreak of encephalitis and respiratory illness among a group of men in Malaysia. The outbreak resulted in 265 cases of encephalitis, 105 of which were fatal. The virus was named after the location in which it was first detected, Sungai Nipah New Village. Affecting pigs and humans, Nipah virus is a member of the Henipavirus genus of the Paramyxoviridae family. The natural reservoir of the virus is argued to be Pteropus fruit bats.
Transmission from bats to pigs is thought to occur when pigs are exposed to the urine and feces of the bats. Humans may contract the disease following exposure to contaminated tissue and bodily fluids of infected pigs. Person-to-person transmission has been suspected in more recent cases.
In humans, infections are primarily encephalitic after an incubation period of 4–18 days. Symptoms initially include fever and headache, followed by drowsiness and disorientation, nausea, weakness, and in some cases, respiratory illness. In 60% of patients, these signs and symptoms may progress to coma within 24–48 hours. In pigs, the virus generally produced only mild illness, characterized by respiratory distress.
WORDS TO KNOW
EMERGING INFECTIOUS DISEASE: New infectious diseases such as SARS and West Nile virus, as well as previously known diseases such as malaria, tuberculosis, and bacterial pneumonias that are appearing in forms that are resistant to drug treatments, are termed emerging infectious diseases.
ENDEMIC: Present in a particular area or among a particular group of people.
HOST: Organism that serves as the habitat for a parasite, or possibly for a symbiont. A host may provide nutrition to the parasite or symbiont, or simply a place in which to live.
STRAIN: A subclass or a specific genetic variation of an organism.
It has been observed that the Pteropus genus of fruit bats are susceptible to Nipah virus infection, but do not develop illness. Populations of these bats are distributed across a wide area, including the northern, eastern and southeastern regions of Australia, Indonesia, Malaysia, the Philippines, and other Pacific islands.
This disease has a wide host range, which accounts for the emergence of Nipah virus as a zootic pathogen. Those people most at risk of contracting the disease are those working in close association with infected pigs in areas of where the virus is endemic (naturally present).
Nipah virus was first implicated in encephalitis in the outbreak of neurological and respiratory disease that occurred on Malaysian pig farms in 1999. Cases also occurred in Singapore in 1999 and were attributed to pigs that had been imported from the infected Malaysian pig farms. Between 2001 and 2005, six outbreaks occurred in India and Bangladesh. These were all in areas where Pteropus fruit bats live, suggesting that the spread of the virus is limited to those areas where these fruit bats are found.
During the initial outbreaks of Nipah virus infection, the antiviral drug ribavirin was used and was deemed helpful in reducing the duration of feverish illness and the severity of the disease. However, the precise clinical usefulness of the drug remains uncertain. The usual treatment for infected persons is intensive supportive care. Researchers have made progress in identifying the way in which the virus enters cells and replicates, and this knowledge could potentially lead to an effective treatment for the virus.
Nipah virus infection may be prevented by avoiding contact with animals known to harbor the infection and by using appropriate personal protective equipment when handling infected tissue. Transmission of the virus from bats to pigs may be avoided by minimizing the overlap of the habitats of these animals, thus reducing the likelihood that pigs will come into contract with bat urine, feces, or partially eaten fruits.
Nipah virus is classified as an emerging infectious disease by the United States Centers for Disease Control and Prevention (CDC). It is considered a cause for public concern due to the significant mortality rates observed following infection, as well as the social impacts of the infection.
Later human outbreaks of the disease in Bangladesh were characterized by a high rate of respiratory disease, which potentially increases the chances of person-to-person transmission and may indicate the emergence of more dangerous strains (types) of the virus. It is assumed that the virus did not emerge suddenly, but has been slowly adapting to humans as a host and therefore poses an greater threat.
Nipah virus infection among pigs carries a significant economic impact. The 1999 outbreak in Malaysia caused about one million pigs to be slaughtered. This loss of potential income exacts an economic toll on both individual farmers and the community as a whole.
Mandell, G.L., J.E. Bennett, and R. Dolin. Principles and Practice of Infectious Diseases. 6th ed. Philadelphia: Elsevier, 2004.
Butler, D. “Fatal Fruit Bat Virus Sparks Epidemics in Southern Asia.” Nature 429 (May 6, 2004): 7.
Pulliam, J.R., H.E. Field, and K.J. Olival. “Nipah Virus Strain Variation.” Emerging Infectious Diseases 11 (December 2005): 1978–1979.
Centers for Disease Control and Prevention. “Hendra Virus Disease and Nipah Virus Encephalitis.” August 23, 2004. <http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/nipah.htm> (accessed March 28, 2007).
Commonwealth Scientific and Industrial Research Organisation (CSIRO). “Fighting Nipah Virus.” May 23, 2006. <http://www.csiro.au/science/ps1so.html> (accessed March 28, 2007).
World Health Organization. “Nipah Virus.” September 2001. <http://www.who.int/mediacentre/factsheets/fs262/en/> (accessed March 28, 2007).