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Chapter 13 of 16

The world is becoming a smaller place for microbes

Influenza in the US • Poliovirus in Canada • Ebola screening • In-flight TB transmission • Malarial deaths in northern countries • Tiger mosquitos travel by ship • HIV in sub-Saharan Africa • Cholera in Peru

Graphs & Maps:

• Frequent flyers (Map)
• Spread of meningococcal meningitis by pilgrims returning from the Haj, 1987 (Map)
• Diseases affecting tourists
• Malaria in the United Kingdom
• Increased international air travel

Initiative: Hi-tech disease mapping

As the number of international airline passengers has soared from two million a year in 1950 to over 1.4 billion today, the world has been slow to recognize the implications for public health.

Deadly airborne diseases such as pneumonic plague, influenza and TB can easily spread in crowded airport lounges, on a jumbo jet or by passengers after their return home. And infectious diseases can also be carried across borders by their animal or insect hosts. Disease does not respect national boundaries.

In the United States in 1977, over 70% of the passengers on board an airliner grounded for several hours were infected with influenza by a fellow passenger.

In 1978 and again in 1992, poliovirus was imported into Canada by people travelling from western Europe. Eleven people were affected by polio paralysis in the first outbreak - all of them people who had refused immunization.

In South Africa in 1996, a health worker was infected with Ebola by a patient who had entered the country to seek medical care during an outbreak in Gabon. The South African government asked WHO to establish a screening system for airline passengers travelling from other parts of Africa.

In the early 1990s, a flight attendant with active TB is believed to have infected up to 23 fellow crew members over the course of several flights. In 1994, a person with active TB is believed to have infected six fellow passengers on a flight from Chicago to Honolulu.

In 1996, travellers returning to the United States and Switzerland developed yellow fever. They had not been vaccinated against the disease.

There have been reports of a surprising number of malaria deaths in northern countries following unrecognized infection through a blood transfusion or a one-off mosquito bite near an international airport. Brussels, Geneva and Oslo have all had recent cases of airport malaria. Malaria deaths are not uncommon among travellers who develop unexpected fever after returning to their home country. In northern countries where the disease is rarely seen, doctors may fail to diagnose malaria in time.

Infectious diseases can cross borders in other ways too. In 1985, the aggressive tiger mosquito - normally found in Asia - slipped unnoticed into the United States inside a shipment of water-logged used tyres from Asia. Within two years the mosquitos - capable of transmitting yellow fever, dengue and other diseases - had established themselves in 17 States.

In sub-Saharan Africa, HIV was spread among migrant workers, who later carried the disease back to their homes, and by lorry drivers, who bought sex at truck stops on their way across the continent.

Tourism, international travel and migration are all helping to spread disease. The number of refugees and displaced people has increased nine-fold over the past two decades. In 1996, as many as 50 million people worldwide had been uprooted from their homes - 1% of the world's population. Refugees and displaced persons living in overcrowded, unsanitary conditions are at risk of outbreaks of cholera and other waterborne diseases.

In 1991 in Peru, a ship carrying contaminated water from Asia in its ballast tanks sparked off a cholera epidemic that spread rapidly throughout South and Central America. About 11 000 people died.

The International Health Regulations require governments to report all cases of three diseases - cholera, plague and yellow fever. The aim is to provide a rapid international alert system for diseases of international public health importance. The system is designed to steer a course between maximum protection against these diseases and minimum interference with world traffic and trade. But many countries fail to report outbreaks - deterred by the threat of potential economic losses. And the rules are difficult to enforce. Today these regulations are being revised and broadened to provide an early warning about outbreaks of any deadly diseases.

An outbreak anywhere in the world must now be treated as a threat to virtually all countries - especially those that serve as major hubs for international travel. Without an active global disease surveillance system in place to provide an early warning of outbreaks, the export of infectious diseases could become a growth industry.