Global Epidemiology

Killer bugs � coming to an airport near you

Increased travel may spur a resurgence of certain deadly diseases

By Marlene Busko

Randy Fernandez, a 17-year-old immigrant from the Philippines presented at a Toronto hospital emergency department with vague, increasingly severe epigastric discomfort. A CT scan revealed a lesion in the small bowel and a subsequent biopsy identified the pathogen as Mycobacterium tuberculosis. Randy's case of tuberculosis (TB) isn't as rare as we'd like to think. Sudden outbreaks of nearly eradicated diseases serve as a reminder that they may still be lurking around close by.

"We've always had pockets of TB, whooping cough, leprosy, malaria and polio in different areas of the world," says Dr Coleman Rotstein, professor of Infectious Diseases at McMaster University. "With people travelling readily, we're getting the spread of diseases that were formerly limited to isolated regions. Often we don't recognize these diseases here, and they're spread, in the way that SARS spread."

TUBERCULOSIS
A third of the world's population is infected with the TB bacillus. After the collapse of the Soviet Union and its healthcare system, the prevalence of TB � especially multidrug-resistant TB � rose dramatically. AIDS is driving the TB epidemic in Africa and is expected to increase rates of TB in Eastern Europe, India and China.

In Canada, 1,704 cases of TB were reported in 2001. Dormant TB infection is most common in immigrants from countries where TB is endemic (62% of cases in Canada), aboriginals and the homeless. In 2002, Nunavut had the highest reported incidence of TB in this country, "largely due to poverty, crowded living conditions and healthcare limitations," says Dr Edward Ellis, Manager of Tuberculosis Prevention and Control, Population and Public Health Branch (PPHB), Health Canada.

PERTUSSIS
Pertussis is making a comeback in countries with high vaccination coverage and low mortality. "More parents started to worry more about the vaccines than the disease. This allowed outbreaks in unprotected individuals," explains Dr Ian Crandall, assistant professor in the departments of Laboratory Medicine and Pathobiology and the Department of Medicine at the University of Toronto.

In Canada, the annual number of reported cases has increased slightly since 1990, ranging from 2,400 to 10,000, partly due to the low efficacy and waning protection of the previously used whole-cell vaccine. Whooping cough now kills one to three infants in Canada per year, usually those who are unvaccinated. "Ensuring the complete immunization of all children remains the most important preventive measure in maximizing control of pertussis," stresses Dr Arlene King, Director of the Immunization and Respiratory Disease division, PPHB, Health Canada.

LEPROSY
The number of worldwide leprosy cases has dropped from 5.4 million in 1985 to less than 1 million in 2001. Leprosy is rare in North America. In Canada, the estimated prevalence of leprosy is 0.6 cases per 100,000. However, with increased travel and immigration from countries where this disease is endemic, cases of leprosy are likely to continue to occur in Canada.

MALARIA
Malaria is returning to regions where it had been eliminated and it's increasingly drug resistant. At least 1 million children die and several million become seriously ill every year in Africa from malaria. Artemisinin-based combination therapies, at $2 US for an adult dose, cost 10 to 20 times as much as old monotherapies such as chloroquine, but are effective in treating malaria that's become resistant to the old drugs. Due to the anticipated increase in travel and the changing distribution of malaria worldwide, the rate of imported malaria by Canadians � generally around 400 cases a year � is likely to increase. Health Canada strongly recommends that travellers consult with travel medicine physicians to determine their need for preventive antimalarial treatment.

POLIO
The WHO aims to stop the spread of polio by 2005. No cases of paralytic poliomyelitis have been isolated in Canada since 1988. At the G8 summit in Kananaskis, Canada pledged to donate $43 million over three years to the WHO and UNICEF to eradicate polio. It recently donated an additional $13 million.

"We had hoped to eradicate malaria and thought we had TB under control, and we should have vaccinated polio and whooping cough out of existence, but we put a man on the moon instead," says Dr Crandall. He also advocates more funding of programs to eradicate these diseases across the globe because they aren't "somebody else's problems."