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India's pneumonic plague outbreak continues to baffle

BMJ 1995; 311 doi: (Published 16 September 1995) Cite this as: BMJ 1995;311:706

The origin of the Yersinia pestis strains that caused pneumonic plague in Surat last year, killing 52 people, remains a mystery, according to an Indian government scientific advisory panel investigating the outbreaks. The Technical Advisory Committee on Plague also told the government that uncharacterised strains of the micro-organism might have caused the outbreak.

The committee reported obtaining pure cultures of Y pestis from sputum samples of patients in Surat with pneumonic disease in September 1994 and detecting Y pestis genes in patient necropsy materials.

“This investigation establishes beyond doubt the identity of the causative agent as Yersinia pestis,” said Professor Vulimiri Ramalingaswamy, former director general of the Indian Council of Medical Research and chairman of the committee. “But its origin in Surat remains an enigma.”

The committee said that biochemical and protein profile studies indicate that the Y pestis isolated in Surat possesses some unique genetic characteristics. The Centres for Disease Control at Fort Collins, for instance, reported a new protein band on three of the Surat strains, and studies at the Pasteur Institute in Paris showed that the strains belong to a new ribotype. Research now underway at the All India Institute of Medical Science in New Delhi also indicates that there are genetic variations among the Surat strains.

The committee also said that animal toxicity studies conducted in India show that the Surat strains have low virulence and that drug tests confirmed their sensitivity to tetracycline. “It is possible that the low virulence of this strain helped keep the number of deaths low,” said Dr Thomas Verghese, a senior epidemiologist and committee member.

It has also charted the sequence of ecoepidemiological events that led to the outbreak of bubonic plague in central India a month before pneumonic plague flared up in Surat: an earthquake in central India upset the ecological balance and paved the way for the transmission of Y pestis from its natural reservoirs into humans.

But the committee has been unable to establish a link between the bubonic outbreak in central India and pneumonic disease in Surat. “We still do not know. It could have been an independent outbreak,” says Ramalingaswamy. Several microbiologists, however, say that the final report of the committee is unlikely to quell the year long controversial debate on the outbreak.

Some public health experts say that the pneumonic plague epidemic in Surat last year did not match features of previous outbreaks. The committee has also conceded that Surat lacked ecological links conducive to an outbreak of plague. And although at least 200000 Surat residents fled the city during the epidemic, no other city reported pneumonic plague.

Scientists also allege that the government has not made public any data that do not support an outbreak of plague: a report by doctors commissioned by the Gujarat state government had concluded that there was “no evidence of person to person, airborne transmission.”

Everyone seems to agree on the need to boost India's disease surveillance mechanism. Warning that early successes in controlling infections have “lulled India into a dangerous complacency,” the committee has urged the government to accelerate the establishment of a national disease surveillance network proposed by epidemiologists (25 February, p 484). It says that public health laboratories need to upgrade their skills in identifying infectious agents.—GANAPATI MUDUR, science writer, New Delhi

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