Up to 16 per cent of the population of Baltimore could have been exposed to leptospirosis, a disease spread in the urine of rats, according to Dr Gregory Glass of the Johns Hopkins School of Public Health in Baltimore. If left untreated, leptospirosis can lead to kidney and liver failure.
Dr Glass warned that the disease could be as common in Britain. "I have no reason to doubt that the incidence in London is any different from here," he said.
Other speakers warned that global climate change could exacerbate the spread of disease. Professor Rita Colwell, president of the American Association, said: "Communicable diseases are resurging. Some factors are obvious. Poverty and of course human migration has contributed to the spread of disease and rodent-carried viruses." But, she went on: "An aspect of infectious disease which has not been considered until recently are environmental factors.
"Malaria with a current worldwide mortality of about 2 million people a year may kill an additional million people annually as temperatures rise and the parasite-bearing mosquito spreads into geographic areas not usually affected."
Some exotic diseases have already spread from their place of origin. Hantaviruses, which can cause hypertension and chronic renal disease, are also being spread through US inner-city populations through the urine of rats, Dr Glass said.
Yet the hantaviruses were originally believed to be exotic diseases. The virus was first detected among US troops during the Korean war. There is also evidence of hantavirus in rats in London, he said.
Dr Glass said the rates of human infection of both hantaviruses and leptospirosis in US inner cities "at least approach those of Third World countries, and the rates are going to go up". Only 50 cases of leptospirosis were reported in the US last year, two of which were in Baltimore. Yet a survey of patients coming to the city's Johns Hopkins hospital showed that 160 people out of every 1,000 were carrying evidence of infection in their blood.
Budgetary cutbacks have meant that many US cities have stopped or reduced their rat control programmes, and there has been a corresponding increase in numbers over the past five to six years.
Leptospirosis causes fevers and muscle pains "which makes it difficult to sort out from the flu", Dr Glass said. While about a third of those infected will show only slight symptoms about two-thirds are severely affected. Because it is not being properly diagnosed, the disease is a needlessly heavy burden on the health care system.Reuse content