THE mysterious death of a dozen tigers (and a deer) in the Nandankanan zoo has been ascribed by zoo officials to the disease Trypanosomiasis. Half a dozen more animals are reported to be infected by the disease.
Even as the report of the inquiry committee was awaited, Lalji Singh, Director of the Centre for Cellular and Molecular Biology (CCMB), a Council of Scientific and Industrial Research (CSIR) laboratory in Hyderabad, raised some fundamental questions. The comments of Lalji Singh, a well-known expert in DNA (deoxyribonucleic acid) fingerprinting and genetic studies of biodiversity, in particular the genetics of big cats, which were made in a telephonic interview, lend an intriguing perspective to the enti re episode of mammalian deaths in captivity.
The most important point that Lalji Singh makes is that Trypanosomiasis is not native to India. So how did this disease get transmitted in the first place? From the reported descriptions of the symptoms, it seems that the disease could have been Trypanos omiasis but it needs to be ascertained whether the diagnosis was correct, he says. It is not known whether the authorities and veterinary scientists associated with the inquiry have been able to isolate the pathogen.
Trypanosomiasis affects all mammals, including humans. Two types of the disease are known: one, prevalent in the Latin American region, is caused by Trypanosoma cruzei, a unicellular protozoan parasite. It is transmitted by the insect called Redwi nd bugs. According to Lalji Singh, T. cruzei is an intra-cellular parasite which leads to defects in blood and muscle cells, including cardiac muscles, causing death. The human form of the disease is called Chagas' disease. Both the disease and th e vector bug are not found in India.
The second variety is prevalent in Africa and is caused by the parasite T. Brucei. This is transmitted by the insect Tsetse fly, which sucks blood and injects the parasite into the body. Unlike the tropical American parasite, this invades the extr a-cellular parts of the body and eventually affects the nervous system, which can lead to death. The parasite load injected is substantial and the degeneration in this African form of Trypanosomiasis is rapid, Lalji Singh says. In humans, the disease is called Sleeping Sickness. The parasite and the vector, Tsetse fly, are also not found in India.
There is no cure for the disease and drugs like the one given by the zoo officials can help if it is detected at a very early stage. Sanitation and hygiene can help prevention. "There is no point in asking for heads to roll. If the disease was prevalent, one could anticipate it, take preventive action or detect the disease at an early stage. Of course, they could have maintained better hygiene," says Lalji Singh.
So the question that has remained unanswered is, where did the disease come from? From the symptoms described, it appears to be the African variety. One possibility, according to Lalji Singh, is infection through animals, such as the lion or the baboon, that were imported from Africa and could have been carriers of the disease. (Apparently India does not import any animals from Latin America.) Even though there are quarantine procedures for imported animals, unless proper diagnostic procedures for Trypa nosomiasis are put in place, the authorities may not even be able to detect the disease even if an animal is a carrier of the infection. Once in the zoo habitat, the disease would spread to all animals (and possibly humans in the zoo environs too, depend ing upon the vector which, as yet, remains a mystery).
Some officials have said that in-breeding has led to the disease. In any case, parasites and the transmitting vectors do not distinguish between in-bred and other animals except for the fact that in-bred ones may be somewhat immuno-compromised, Lalji Sin gh says.
From the biological point of view, this parasite is extremely interesting, Lalji Singh says. This is because for a unicellular organism, the genome size is extremely large consisting of 10 million base pairs (the human genome is three billion bp) and con tains 1,000 genes, a very high number. As a result, the parasite is able to invade any immune system. It presents a tremendous antigenic variation and easily evades the immunity mechanism, making it impossible to design a vaccine.
In TIGR, a genomic research centre in the United States (which, incidentally, is run by the wife of Craig Venter of Celera Genomics who hit the headlines recently in the human genome sequencing effort), a major programme to sequence the Trypanosoma paras ite genome is under way under Nazibul Sayed, according to Lalji Singh. As in the human genome case, this too has led to "public vs private" debate. Lalji Singh points out that genomic data of the parasite are not in the public domain to any significiant extent.
Apparently, one of the scientists of the CCMB, Tushar Vaidya, who has considerable knowledge of the genomics of Trypanosma, wanted to do a DNA analysis of samples from the infected animals. "I had written to the zoo authorities to allow us to draw blood or take samples of tissues, bone or hair from the dead animals. We have got no reply. There have been conflicting reports about how the dead animals have been disposed of. If they were buried we can still exhume and obtain samples. We can easily do an an alysis and find out the strain of the parasite," says Lalji Singh.
According to Lalji Singh, there are five or six strains of the parasite. The question that arises, therefore, is whether any virulent Indian strain has evolved. "We need to characterise this strain but this is easier said than done because no animal syst em has been evolved to study this. It has to be done in-vitro," he says. "But more pertinently," he points out, "whether or not there is an Indian strain, we do not have the transmitting agent as well in this country. So what is the vector of this diseas e? Mosquito, as has been mentioned in some reports, is not known to be a carrier of the disease. So there are many basic questions which need to be answered but it is not known whether the inquiry committee is asking the right ones."
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