8 February 2005
The Nipah paramyxovirus was confirmed last month (January 2005) by US CDC labs to be causing an outbreak of encephalitis in Bangladesh for the 5th time in four years (2001, 2003, 2004 (twice), 2005). When Nipah was first discovered in 1999 in Malaysia (including the town of Nipah), and then in Singapore, it was reported not to spread from person-to-person. In recent publications, however, Nipah virus does appear to spread person-to-person and to cause severe pneumonia, as well as encephalitis, a concerning combination that suggests a difference exists in this virus compared with the original 1999 Nipah virus.
Chest x-rays showing severe bilateral respiratory disease, and evidence of person-to-person transmission of Nipah virus in family members and other close contacts (including one rickshaw driver who transported a patient) from the Feb 19-April 16, 2004 outbreak in Faridpur district of Bangladesh were published in the June 2004 Health and Science Bulletin of the International Centre for Diarrheal Disease Research (ICDDRB), Bangladesh (as noted by Dr. Dudley on ProMED-mail 26 Jan 2005).
This study was a collaboration between investigators from Bangladesh, WHO, Malaysia, Health Canada, and the US CDC. They noted that 33/36 (92%) patients with Nipah infection had close contact with at least one person with confirmed or probable Nipah infection, suggesting respiratory transmission via large droplets. 27/36 patients (75%) died. Chest X-rays were done in six patients and were consistent with acute respiratory distress syndrome (ARDS).
In the December 2004 issue of the Emerging Infectious Disease Journal published online at www.cdc.gov, US CDC investigators (Hsu V. et al.) reported that retrospective studies suggested that person-to-person spread of Nipah virus may have also occurred in Bangladesh during the 2001 and 2003 outbreaks.
Genetic sequencing of the 2004 and January 2005 Nipah viruses from the outbreaks in Bangladesh, and comparison with the original 1999 outbreaks in Malaysia and Singapore have not yet been published. This sequencing information will prove useful in trying to explain the apparent change in clinical and transmission characteristics of Nipah virus between 1999 in Malaysia/Singapore and later outbreaks in Bangladesh. Media reports last month suggested that a different strain of Nipah virus has been found in Bangladesh compared with the first emergence of the virus in Malaysia, but specific scientific data are awaited to establish this possibility.
No antiviral drugs have been shown to be clinically helpful, although ribavirin has activity in vitro against the virus. Flying fox bats of the genus Pteropus appear to be an animal reservoir for Nipah, while other animals can be infected and spread the virus to humans as evidenced with the original 1999 outbreak in pigs, pig farmers, and abattoir workers. According to CDC Special Pathogens Branch website: ‘Illness with Nipah begins with 3-14 days of fever and headache followed by drowsiness, confusion, and sometimes progression to coma within 48 hours. Some patient have a respiratory illness during the early phase of their illness.’ (CDC website accessed 8 Feb 2005).
If Nipah virus does cause respiratory disease, severe or mild, and is spread by the respiratory route, large droplet or smaller droplet nuclei aerosols, then infection control measures including use of masks or fit-tested N-95 respirators, and isolation measures, may prove important in decreasing spread of Nipah virus.
The theoretical potential for a virus causing encephalitis, pneumonia, and a high case fatality rate, in conjunction with person-to-person respiratory transmission, to be used intentionally to trigger outbreaks is evident.
Daniel R. Lucey, MD, MPH