Last Thursday afternoon, David Hill ’73, director of the London-based National Travel Health Network and Centre (NaTHNaC), presented a view of the global spread of disease in a lecture titled “Travel and the Spread of Infectious Diseases.” The lecture was sponsored by the Public Health Alliance.
Hill, who holds an honorary professorship at the London School of Hygiene and Tropical Medicine, is currently teaching a Winter Study course titled “Global Health: Why We Should Care,” which he also taught last year. In the Wege Auditorium on Thursday, he discussed the complications and risks surrounding travel and the spread of infectious disease, which resonated with the audience in light of the H1N1 influenza pandemic.
According to Hill, public consciousness of the influence of migrating infectious diseases only began to approach its current levels around 1995, when a number of influential books and popular magazines began to document cases such as the breakout of the Ebola virus in Zaire. Since then, he explained, knowledge of such diseases has increased as technological and economic forces have made them more of a threat.
Though technology has aided the development of vaccines, and the economic clout of some countries has helped third world nations gain access to some of those vaccines, the vaccines have also played a part in developing new and more resistant viruses. Hill named climate change; globalization of trade, especially for food; the widespread use of antibiotics; and increases in international travel as factors that have driven the development and spread of infectious disease.
Hill noted that the emerging infectious diseases “are primarily animal diseases that have moved into the human reservoir because of things that we have done,” leading to dangerous results. “If the ability to infect humans combines with the ability to cause death, you don’t get a very good outcome,” he said.
National and international efforts have had varying degrees of success in curbing and preventing the spread of disease. Nevertheless, general efforts to prepare for infectious disease can be helpful even if they don’t hit the nail on the head. Because of its preparation for the spread of avian flu, Hill explained, the United States was “lucky” two times over when H1N1 became an issue. Not only was the case-fatality ratio (the number of deaths per infection) for H1N1 far lower than that of the avian flu – about 0.02 percent compared to 60 percent, respectively – but the US also had an existing infrastructure for dealing with an influenza epidemic.
Attempts to slow the propagation of disease are, however, often dishearteningly ineffective. Hill presented a telling set of graphs mapping the number of H1N1 cases in the United Kingdom classified by their status as imported, secondary (import-related), indigenous or of an unclear source. The spread of disease clearly started with just a few imported cases, brought over on planes from Mexico or by people who had visited the country. As time progressed, though, the number of imported cases gradually fell off, replaced by exponentially increasing numbers of secondary and indigenous cases. Despite the best efforts of agencies like NaTHNaC to police the travel of infected people, H1N1 prevailed in what Hill called its “sloppy, capricious and promiscuous” way.
In line with the global scope of his Winter Study course, Hill discussed a number of current health crises that are largely in the past for the United States and the United Kingdom. For example, one-third of the world’s population is currently infected with tuberculosis, and the US has instated entry checkpoints to prevent any additions to its 12,700 current cases. However, Hill pointed out that most foreign-born tuberculosis cases only become clinically apparent five or more years after entry, so such screening is effectively useless. Efforts have been made to address this issue, such as the 2005 International Health Regulations that shift focus to controlling the source of disease by monitoring vaccination records and disease trends before travel, rather than policing disease at the borders of countries.
Hill then turned to a discussion of polio. Though completely eradicated in the United States, this disease is still devastating the health of children in India and many African countries. Hill called the presence of polio in these countries a result of both programmatic failure and immunologic failure. In Nigeria, the polio vaccine has been boycotted based on the belief that it causes sterility and is tainted with HIV, while in India, many children’s bodies are not receptive to the vaccine.
At the conclusion of Hill’s presentation, an important question lingered. Considering the effect of travel on the spread of disease, Hill asked, should we still be visiting foreign countries? In a statement given last May, the World Health Organization did not recommend travel restrictions. All things considered, air travel has been a boon to the development of the global community and the enjoyment of Euro-trotting young adults. The hope remains that cures can be developed as quickly as human activities generate new viruses.