Cybermed Update June 2000

 

Nipah Virus

The culling of pigs seem to have resumed or in the process of being done so. We had reports in Gopeng, Perak (Dept begins culling of pigs in Gopeng (17 June 2000) )and more recently in Sarawak (Sarawak to cull pigs if blood samples confirm virus (27 June 2000))of pigs being quarantined and awaiting outcome of Serum Neutralisation Tests (SNT) (Fate of pig farmers to be known in two weeks' time) from Australia. To compound this, we had misleading reports either as to the mode of spread or control measures of this disease. The press in some instances continued to call it the JE or JE/Nipah outbreak even after a Malaysian discovered the virus and numerous papers had been published in top journals such as Science, Lancet, New England Journal of Medicine, Journal of Infectious Disease, MMWR to name a few. This hesitation on our part to recognise that by and large the outbreak was due to Nipah virus has come under strong criticism from the Scientific community within Malaysia but as well as from abroad (Promed). Comments by the Promed moderator is appended below. (edited) (24 June 2000)

"Let me emphasize that we know of no reason to believe there is an outbreak of Nipah virus occurring in Malaysia or anywhere else at this time. The antibodies may be a result of remote infections, for example from last year. Epidemiologic information regarding not only illnesses but the ages of the pigs with antibody would be helpful. Additionally, some of the reports emanating from Malaysia have mentioned Japanese encephalitis. Either the media have misunderstood or the people using these words have no idea what they are talking about or there is some Japanese encephalitis occurring in Malaysia. As we have flogged this for a year, we will not comment further than to say JE virus has nothing to do with Nipah virus. "

"It will, perhaps, be unfortunate if the authorities in Malaysia do not understand the significance of antibody to Nipah virus in healthy, recovered pigs. I am certain that Australian and U.S. scientists would provide needed information and background, if requested, and I am equally certain that neither of those groups will comment to ProMED-mail on any aspect of this sensitive situation; that is understandable and reasonable. It is the Malaysian government authorities and media who must improve their grasp of the situation once and for all, and soon. If antibody alone will be used as a reason for culling pigs, then we have a political, not a scientific situation. "

The question whether the test is for antigen or antibody as seen above is surfacing again. ( see previous article in Berita MMA).

Nipah virus (NV) was officially named on 10th April 1999. The virus belongs to the family Paramyxoviridae and is very closely related (molecular)to another virus called Hendra virus (HV). "Phylogenetic analysis demonstrated that although HV and NV are closely related, they are clearly distinct from any of the established genera within the Paramyxoviridae and should be considered a new genus."

The natural reservoir for the disease was recently confirmed to be in Island flying foxes (Pteropus hypomelanus) and the Malayan flying fox (Pteropus vampyrus) and possibly in other bat species, but to a lesser extent. Pigs, other animals and humans are the host. I quote an interview in The STAR (Down)by See Yee Ai for an excellent overview of this disease.

Contrary to public perception, Nipah didn't emerge from nowhere to become a killer. Scientists may not have all the pieces of the puzzle yet but the general picture seems to be that Nipah may have been around pig farms as early as 1995, slowly adapting to pigs and humans as hosts. Among the evidence: sporadic cases of viral encephalitis among pig farmers and cases of pigs falling sick of unknown causes.

"Most of the encephalitis cases were caused by known agents like the Japanese encephalities (JE) virus. But a small number were due to unknown causes. We have to go back and test all these question mark cases," says Prof Lam Sai Kit, head of the medical microbiology department at Universiti Malaya. (Prof Lam, together with Dr Chua Kaw Bing, was responsible for the isolation of the Nipah virus.)

Another piece of the puzzle was the JE outbreak in Tambun, Perak in 1997 in which one farmer died. The outbreak died down on its own after a few months. Doctors suspect that it may have been Nipah even then. But why wasn't the virus so virulent then? Maybe the virus hadn't fully adapted to humans as a host at that time. Nevertheless, the emergence of unusual illnesses among pigs correspond well with what scientists know of a virus' adaptive period. "Paramyxoviruses usually take a few years to adapt to a species before it causes damage," says Dr Abdul Aziz Jamaluddin, research director of the Veterinary Research Institute (VRI) in Ipoh. After a few years of adaptation and infection, Nipah became virulent enough to kill both their pig and human hosts. That was probably why the outbreak in Perak and Negri Sembilan took off with such severity in late 1998. That and because pigs were involved.

Prof Lam believes that pigs were a key link in Nipah infection of humans. "Without the pigs, the outbreak probably wouldn't have happened in this magnitude," he says. Dr Aziz agrees. "Pigs act as mixing vessels. Because they are the only mammals raised in large concentrations, they give opportunity for diseases, not just Nipah, to spread quickly," he says. Other animals like polo horses, cats, dogs and rats were infected but they died without spreading the virus. In pigs, the virus multiplied but didn't always cause any illness--making it difficult to detect. The pigs in turn, secreted the virus in their respiratory droplets and urine. "When farmers came into contact with the pigs, they were infected with the virus," says Prof Lam. Close contact with pigs is now confirmed as the main source of infection. All cases of infection, including those in an abattoir in Singapore and a laboratory in Ipoh involved pig contact.

In the case of the laboratory workers, "The infection probably happened in the early days of the outbreak, when the Health Ministry thought it was JE," says Prof Lam. Since JE was spread by mosquito bites, laboratory workers probably didn't expect to be infected through animal tissue. Since then, all Nipah research is done in P3 facilities--biohazard laboratories for work done with agents that may cause serious or potentially lethal disease via respiratory transmission. However, there is no reason to believe that Nipah can be spread through the preparation or consumption of pork. Chances of human to human transmission of the virus is low. But it can happen, nonetheless. According to Prof Tan Chong Tin, a neurologist at Universiti Malaya, there were three cases of medical care-givers being tested positive for Nipah. There were anomalies in one of their MRI brain scans--indicating that the care-giver was infected. Again, the assumption that it was JE may have caused the infection as care-givers were unaware that they were handling a virus that could spread through the patient's bodily fluids. Since then, the Universiti Hospital team has come up with a protocol to reduce the risk of Nipah transmission to care-givers.

For a complete update on what we know of this disease, I suggest reading the following articles. All and more can be assessed at http://www.vadscorner.com/paramyxo.html .

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