Zoonosis Outbreaks

New outbreaks of zoonotic diseases continue to occur as the human-animal interface grows.  Destruction of animal habitat and human population sprawl increases contact between humans and animals. Humans can be exposed to new, unexpected zoonotic diseases or re-emerging previous diseases.

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Zoonoses that were previously limited to certain geographical locations can spread due to globalization of markets and increased worldwide travel.

Because of this, the World Health Organization (WHO) emphasizes the need for coordinated worldwide responses to new infectious agents in order to prevent epidemics. WHO was instrumental in limiting recent outbreaks of the Ebola virus and avian influenza.


Ebola is a rare, but highly deadly, disease caused by infection with one of five strains of the Ebola virus. The first outbreak of Ebola was in 1976 near the Ebola River in the Democratic Republic of the Congo. Periodic outbreaks continue to occur throughout Africa.

The host species for the Ebola virus are thought to be bats, although this has not been proven. Ebola is highly contagious, and exposure to the virus most often occurs through direct contact with the blood or bodily fluids of an infected patient.  It can also occur through direct contact with an infected patient’s objects, such as bedsheets, syringes, or clothes.

Although much less common, the virus can also be transmitted to humans through contact with bats or by handling contaminated meat from wild animals. The symptoms of Ebola typically appear 21 days after exposure and include fever, headaches, diarrhea, and bleeding.

In 2014, West Africa experienced the largest Ebola outbreak of all time. Due to it’s highly contagious nature, transmission of the virus quickly spread to areas of Liberia, Sierra Leone, and Guinea.

In total, there were about 26,000 cases of Ebola and nearly10,000 deaths in those three countries over a 1-year period. The 2014 outbreak was particularly serious because it affected urbanized areas, whereas previous outbreaks occurred in remote villages that were easier to contain.

Effective control of the virus requires extensive surveillance, tracking, and reporting of new cases. In addition, education of the general population is essential for minimizing exposure risk through proper handling of infected patients or items and limiting travel.

Avian influenza

H5N1 is a highly pathogenic strain of the avian influenza virus found among domestic poultry stocks in Asia and the Middle East. Outbreaks of H5N1 began in the 1990s, and the H5N1 strain was isolated in 1996 from a goose in China. H5N1 avian flu, which is highly contagious and deadly in birds, spread rapidly throughout Asia.

Although human infection with H5N1 is rare, people can contract avian flu after direct contact with infected birds. The first human cases were reported in Hong Kong in 1997. Since 2003, over 650 cases of human infection with H5N1 have been reported in over 15 countries.

Approximately 60% of people infected with H5N1 have died. Variants of H5N1 have arisen that are particularly infectious to mammals and migratory birds. This has led to the rapid spread of the virus throughout Asia, the Middle East, and Europe.

To date, the avian flu is not spread from person to person. However, the frequent mutation rate of flu viruses combined with the highly pathogenic nature of H5N1 in birds is cause for alarm. Scientists fear a mutated form of H5N1 may arise that is contagious in humans and can be spread through sneezing or coughing, leading to the possibility of a worldwide epidemic.


Further Reading

Last Updated: Apr 23, 2021

Susan Chow

Written by

Susan Chow

Susan holds a Ph.D in cell and molecular biology from Dartmouth College in the United States and is also a certified editor in the life sciences (ELS). She worked in a diabetes research lab for many years before becoming a medical and scientific writer. Susan loves to write about all aspects of science and medicine but is particularly passionate about sharing advances in cancer therapies. Outside of work, Susan enjoys reading, spending time at the lake, and watching her sons play sports.


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