• Viral Infections
• Screening & Prevention

While infectious diseases are no longer a major cause of mortality in developed countries, new viral infections continue to emerge due to our globalizing and changing world, as well as improved detection methods. In the 2011 ICAAC lecture, Albert Osterhaus, PhD, Erasmus Medical Center, Rotterdam, The Netherlands, made the point that, “the human species is just another animal species that really belongs to an ecosystem.” Public health, animal health, the food supply, world economies, and biodiversity all depend on anticipating and controlling new viral outbreaks [Kuiken T et al. Science 2005].

Contributing factors for viral crossover from animals include animal contact, human behaviors, urbanization, air travel, wars, poverty, medical practices, and viral adaptation. The ongoing AIDS pandemic is a powerful example of the devastation that can arise from the passage of animal viral strains to humans, as HIV-1 and HIV-2 originated in chimpanzees sooty mangabeys, respectively.

Prof. Osterhaus cautioned that vaccine success comes with potential risks. The eradication of smallpox is perhaps the twentieth century's major medical achievement, but now we are seeing a rise in other Orthopoxviruses in humans, including cowpox and monkeypox, which is fatal in up to 5% of cases [Stittelaar K et al. Nature 2006; Pelkonen PM et al. Emerg Infect Dis 2003]. Notably, this year marks the second successful global eradication of a mammalian virus, Rinderpest, a morbillivirus viral disease in cattle that is closely related to measles. Other morbilliviruses, however, continue to cause deadly outbreaks among animals year after year, such that even as strides are made toward the global eradication of measles, the possibility of emergence of a human morbillivirus from the animal world is strong and discontinuation of measles vaccine may not be recommended, even if measles is eradicated.

Prof. Osterhaus emphasized that the discovery of new viruses requires a team approach that utilizes clinicians, pathologists, epidemiologists, and laboratory evaluation with both classical virological and novel molecular techniques. The discovery of the severe acute respiratory syndrome (SARS) coronavirus involved identifying a new clinical syndrome, culturing and sequencing the SARS virus, creating an animal model of disease, and then testing antivirals in infected animals. Epidemiologists traced the mammalian source to a similar virus in carnivores in live animal markets in Hong Kong and China, which likely received the virus from bats. Since bats constitute 60% of all mammals on the globe, the virus can be spread quite easily.

Another virus that required fast, coordinated action was West Nile virus (WNV) which was introduced in the United States (US) in 1999, likely via air transport of infected mosquitoes, and spread rapidly across the US via mosquitoes as vectors and birds as intermediate hosts. The first serodetection of WNV in Europe was in 1958 in Albania. With recent cases and virus isolation on several European borders, Prof. Osterhaus and his team are following WNV closely.

Other potentially threatening emerging viruses include human metapneumovirus (hMPV), chikungunya virus, Hendra and Nipah viruses, and avian flu. hMPV crossed the species barrier from birds over 200 years ago and is currently responsible for 10% of the severe respiratory infections in young children. Chikungunya causes a severe flu-like illness and has the potential to spread widely within southeastern US, which shares the same mosquito vector with the northern Italian town where it emerged in 2007. Transmitted from fruit bats, outbreaks of Hendra virus in horses in Australia and the related Nipah virus in pigs in Malaysia caused hundreds of deaths among farmers and handlers in the late 1990s and continues to cause disease throughout Bangladesh [Luby SP et al. Emerg Infect Dis 2009].

Avian flu represents a crossover from birds (or sometimes pigs) to humans, and has only occurred in sporadic, isolated cases to date (Table 1). Although avian flu is highly pathogenic and frequently fatal, a pandemic would require that the virus develop better human-to-human transmissibility. Unfortunately, mutant H5N1 strains that have been created in the laboratory have been shown to be transmissible between ferrets, an indication that human-to-human spread could evolve [Munster VJ et al. Science 2009].

Prof. Osterhaus concluded by urging international coordination around outbreaks, collaboration between public and private sectors, and use of all available technology for effective control of emerging infections.

• © 2011 MD Conference Express