Risks From Animal Diseases Growing
Diseases Spread by Animals Affect Millions of People a Year, Study Shows
Nov. 10, 2006 -- Diseases spread by birds, mosquitoes, cattle, and other
animals are a growing problem for humans -- affecting millions of people a
year, according to a new study.
The recent outbreaks of bird flu and mad cow disease have raised
awareness of the danger of diseases spread by animals to humans, known as
zoonotic viruses, the researchers say.
Although those two new diseases have affected a relatively small number of
people, more common zoonotic diseases like dengue fever and rabies kill tens of
thousands of people each year worldwide and appear to be on the rise, the
For example, during the study period from 2000 to 2005:
- Rabies, spread by infected dogs, bats, rats, and other animals, killed an
estimated 30,000 people.
- Dengue virus affected 50 million people and killed approximately
- Japanese encephalitis virus, transmitted by mosquitoes,
was responsible for an estimated 50,000 illnesses and 15,000 estimated
- Lassa fever, a serious viral infection spread by contact with the feces or
urine of infected rodents, affected up to 300,000 people and killed about
- SARS, believed to have originated in palm civets and/or horseshoe bats,
killed 774 of the 8,102 people infected.
"There has been a global resurgence in the dengue virus -- which is
transmitted between monkeys in the jungle by the mosquitoes that feed on
them," says researcher Jonathan Heeney, in a news release.
"The cycle can move into nearby urban areas, where it can then be
transmitted from person to person by mosquitoes," says Heeney, chairman of
the department of virology at the Biomedical Primate Research Centre in the
Netherlands. "This has been attributed to regional population growth around
large cities, increased transportation, and failing public control
Even zoonotic viruses for which there are preventive vaccines -- like yellow
fever -- continue to pose a threat and affect an estimated 200,000 people,
according to the World Health Organization.
Viruses spread among animals become a serious threat to humans when they
adapt for human-to-human transmission.
About a quarter of the diseases originally spread only among animals are
capable of readily spreading from human to human, such as measles and HIV.
In the study, published in the Journal of Internal Medicine, the
researchers analyzed the number of deaths and illnesses worldwide caused by
diseases spread by animals from 2000 to 2005.
The results showed one of the most widely publicized emerging zoonotic
diseases, H5N1 bird flu, killed nearly half of the 145 people
infected with the virus during the study period.
Though most of the attention has focused on the potential for human-to-human
transmission of the bird flu virus, researchers say the risk posed by
diseases currently spread from animals to humans is also great. Many have no
known vaccine or cure.
Preventive Effort Needed
To prevent emerging zoonotic diseases from becoming major public health
threats, Heeney calls for greater cooperation between health and medical
experts from various fields.
"The early identification, control, and prevention of re-emerging viral
zoonotics lie not only with clinicians and public health experts but, more
importantly, with veterinarians, animal scientists and wildlife
ecologists," he says.
"They are in the best position to identify trends and patterns, such as
increases in the number of deaths of wild or domestic animals. Awareness and
surveillance of eco systems will play a key role in identifying and controlling
new, emerging, and re-emerging viral zoonotics," Heeney says.