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ASIA: An Old Foe, Malaria, Could Hold the Key to SARS – Experts

Rahul Goswami

SINGAPORE, May 20 2003 (IPS) - South-east Asian countries like Singapore have begun to cautiously hope that they have weathered the worst of the SARS outbreak, although it still looms large as a new and deadly health threat.

South-east Asian countries like Singapore have begun to cautiously hope that they have weathered the worst of the SARS outbreak, although it still looms large as a new and deadly health threat.

More than two months after cases began spreading rapidly in the region, Taiwan is still reeling from spikes in the number of cases and deaths related to the Severe Acute Respiratory Syndrome (SARS).

Singapore, which like other countries has been seeing a drop in the number of new infections, was hoping to be declared free of SARS on May 18. But a single new case reset the counter.

The city-state’s health minister, Lim Hng Kiang, advised Singaporeans to "take this in their stride because if you ask yourself what has physically changed – nothing much, because this case has been isolated in our hospital".

But away from the region, new thinking from India is questioning both the reasons for the virulence of SARS and responses to it.

The questions challenge current knowledge about the outbreaks and the relationship between human populations and opportunistic infections. They also seek explanations for why the impact of SARS is mild in certain regions, but far more dangerous than the flu in others, with a fatality rate of 13-15 percent.

These are crucial questions, because the deaths from SARS continue. As of Monday, the World Health Organisation (WHO) reported 7,864 cases of SARS worldwide, and 643 deaths attributed to it. More than 95 percent of these cases and close to the same percentage of deaths recorded from it have taken place in mainland China, Hong Kong, Singapore and Taiwan.

The coronavirus, which has now been confirmed to be the cause of SARS, is not easy to detect. Medical researchers from The Netherlands to Canada have expressed awe at the speed with which the virus has been proven to be the cause of SARS – in comparison, it took nearly two years to confirm HIV as the cause of AIDS.

Yet, as the latest Singapore case demonstrates, it was five days before a diagnosis of atypical pneumonia could be confirmed as the dreaded new coronavirus.

Dr Ling Ai Ee, virologist with the Singapore General Hospital, said that detecting the SARS virus from blood tests was difficult as these are "a little bit less sensitive". As was seen in Hong Kong, the virus is more easily detected in stool samples, but then only in the second week of infection.

Experts from South Asia offer ideas on how the human body’s defences might be strengthened against SARS. It is an old foe of those who live in tropical and developing countries in South and South-east Asia that could provide a glimpse into the methods of the SARS virus and that old foe is malaria.

Medical professionals have said that the endemic presence of infections of falciparum malaria – one of the four life-threatening types of parasitic malarial diseases transmitted by mosquitoes – in some regions in Asia may have contributed to the milder reaction to SARS there.

Dr James da Costa, a pathologist based in Mumbai, India, has been studying falciparum malaria for the last nine years. "It has the highest mutation amongst parasites," he said in an interview, "second only to leishmaniasis, but the pattern has changed in the last few years”.

Leishmaniasis is a parasitic disease transmitted by the bite of some species of sand flies, and more than 90 percent of the world’s cases occur in Bangladesh, Brazil, India, Nepal and Sudan.

"Falciparum has produced symptoms identical to SARS," said da Costa. "Over the last five months I have noticed acute respiratory distress syndrome, as there was during the Surat plague." That took place in 1994, in the western Indian city of Surat in Gujarat state.

More pertinently, da Costa said that malaria has been known to alter the immune response of people.

"It protects against the severe manifestation of other viral infections, by suppressing an over-reaction of the immune system," he said. "It is this immune response of the individual host, and not the presence of the virus alone, which determines the severity of the symptoms."

Indeed, that is one of the aspects of the SARS outbreak that has virologists questioning the speed and spread of the outbreak.

Dr Kalyan Banerjee, virologist and former director of the National Institute of Virology in Pune, India, questions why the virus affects adults far more severely than it does children. "This aspect needs very much more epidemiological work," he said in an interview.

Although the coronavirus that causes SARS is said to be a new type, previously unknown, Banerjee pointed out that the virus "may have been ecologically located in South-east Asian or East Asian countries". He also said that "it is serologically related to other viruses".

Asked about the susceptibility of ethnically diverse populations to the SARS virus, and the public health responses in a populous country like India, Banerjee said much study needs to be done about whether some groups of people may be more prone than others to some diseases.

In India, the number of suspected cases reached 20 before WHO declared the country safe from SARS, but not before scares of an epidemic had shaken the country and its health authorities.

"In the history of infectious diseases, that some ethnic groups are susceptible and others are not is well-known – it is a curious effect," explained Banerjee. However, he cautioned, "Right now it is too premature to make a conclusion about who it affects."

The virologist emphasised that "such a virus cannot be generated sui generis – spontaneously". Banerjee asked: "What was the ancestral virus? If the virus has been fairly benign, and has not been doing much clinical damage, the possibility is that it has been present (in our habitats)."

As da Costa said, “Simple solutions are being missed. The genetic variant of falciparum is being missed.”