Emerging and re-emerging viruses
An emerging virus can be defined as an infectious virus whose incidence is increasing following its first introduction into a new host population; a re-emerging virus is one whose incidence is increasing in an existing host population as a result of long-term changes in its underlying epidemiology. Emerging infections have an enormous impact on public health, food supply, economics, and the environment. Human mortality due to AIDS (HIV) has risen to about 20 million. Livestock production has been negatively affected by the direct mortality of animals from emerging infections and depopulation policies to control the pathogen and protect the safety of international trade. The environmental impact is of concern in large outbreaks in specific species and especially for endangered species that may be driven close to extinction.
Emergence or reemergence of viruses is often evoked by environmental changes like climate change or ecological changes which influence animal life. Intensive agricultural practices, involving increasing numbers of animals in close proximity, or multiple species farmed within the same geographical region have given rise to opportunities for viruses to cross species barriers between hosts not normally in close proximity such as with Nipah virus and SARS-Corona virus infections.
Emerging and re-emerging zoonotic viruses
A growing number of viruses of animal origin are known to cause serious disease in humans. Rabies virus is probably the best known viral zoonosis, and this virus still causes around 31000 fatal infections per year in Asia. In the past history humans have been infected with a number of unrecognized viruses of animal origin, and many individuals have died of infection before a viral pathogen was discovered (ie HIV, SARS-CoV). Over the last few decades outbreaks of viral zoonoses have occurred each year and in all parts of the world. Viruses of unknown zoonotic potential have emerged and wellknown zoonotic viruses have re-emerged. The increasing globalization, with not only people circumnavigating the globe, but also animals and their produce, has provided a mechanism for unprecedented spread of infections at speeds that could challenge the most stringent control mechanisms. Furthermore, the continual encroachment of man into natural habitats through population expansion requirements to tourism, brings mankind into new ecological environments, giving opportunity for new zoonotic exposure. Climatic changes have seen the expansion of compatible conditions for disease vectors, further molding the dynamics for new, emerging and re-emerging zoonoses.
Public health awareness and public health protection
Risks from zoonotic disease are almost impossible to avoid. People are at risk in their homes from airborne transmission of zoonoses, possibly from a passing agricultural vehicle; our food may provide a vehicle for transmission of food-borne zoonoses; Excretions from hantavirus infected Bank Voles on a camping site, may be stirred up to infectious aerosols causing human disease. We may take our children to a “petting zoo” or “petting farm” giving close proximity and ideal chances for transmission. Owning family pets opens up a kalidescope of potential zoonotic infections, especially where the pet is more “exotic”. Recreational activities such as watersports could put you at risk for acquiring norovirus infections, with the viruses remaining viable in aquatic environments for months. Other sporting activities such as hunting have been associated with Hepatitis E virus infections. Travel to other countries opens a range of new potential zoonotic exposures, both direct through contact or indirect through formites, food or arthropod vectors. Increasingly exotic locations are being sought with associated “exotic zoonoses”.