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10 Million People A Year Are Affected By Zoonotic Viruses Spread By Non-human Hosts

13 Nov 2006

Doctors and veterinarians need to work together to tackle the increasing
global threat of zoonotic viral diseases spread by non-human vertebrate
hosts - including dogs, cattle, chickens and mosquitoes - according to a
review in the November issue of Journal of Internal Medicine.

An estimated 50 million people acquired zoonotic diseases between 2000
and 2005 and up to 78,000 have died, reports Dr Jonathan Heeney, Chair
of the Department of Virology at the Biomedical Primate Research Centre
in the Netherlands.

And the diseases responsible for the majority of zoonotic illnesses, and
a third of the deaths in the study period, appear to be increasing. This
is particularly worrying because there are no effective vaccines for
some of the most common zoonotic viruses.

"For instance 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. The cycle can move into nearby urban areas where it
can then be transmitted from person to person by mosquitoes" says Dr Heeney.

"This has been attributed to regional population growth around large
cities, increased transportation and failing public control measures."

Recent publicity about the risk of an H5N1 (bird flu) epidemic - which
killed just over half of the 145 people infected during the study period
- has centered on the risk of human-to-human transmission. It has also
stressed the increased risk that humans face from living in close
proximity to large concentrations of birds.

"Viral infections with zoonotic potential can become serious killers
once they are able to establish the necessary adaptations for efficient
human-to-human transmission under conditions sufficient to reach
epidemic proportions" says Dr Heeney.

"That is why it is so important for experts from all walks of medicine
to work more closely together.

"Vaccines have been very successful at eradicating devastating human
disease such as smallpox. But we need to be vigilant and ensure that
emerging diseases such as monkeypox don't find immunological niches in
generations who are no longer vaccinated against diseases like smallpox.

"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.

"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."

Zoonotic killers between 2000 and 2005 included:

* Rabies, which killed an estimated 30,000 people

* Dengue Virus, which affected 50 million people and killed
approximately 25,000

* Japanese Encephalitis Virus, with up to 50,000 estimated cases and up
to 15,000 estimated deaths

* Lassa Fever, which affected up to 300,000 people and killed about 5,000

* SARS Corona virus, which killed 774 of the 8102 people infected

Even a zoonotic virus like Yellow Fever - for which an effective vaccine
exists - is estimated to affect 200,000 people, according to the World
Health Organization.

"It should be stressed that only about a quarter of zoonotic pathogens
are readily spread from humans to humans" says Dr Heeney.

"But it is believed that in extreme situations when certain animal
viruses transmit to humans they may mutate and adapt to the new host so
effectively that they may become almost exclusively spread from humans
to humans. This seems to have already happened with measles and the HIV
virus.

"Although the number of cases of human bird flu deaths is relatively
small when compared with diseases such as Rabies and Dengue, the
publicity generated by those deaths has helped to raise awareness of
zoonotic diseases.

"We now need to build on that awareness and ensure that the
international medical community monitors changes in animal and human
health very carefully to ensure that we identify and control any new,
emerging and re-emerging zoonotic viruses."

###

* Zoonotic viral diseases and the frontier of early diagnosis control
and prevention. Heeney J L. Journal of Internal Medicine. Volume 260,
pages 399 to 408 (November 2006).

* Journal of Internal Medicine (JIM), which can trace its origins back
to 1863, is edited by Dr Ulf de Faire from the Karolinska Instutet,
Sweden. It publishes original clinical work focussing on general and
internal medicine, together with reviews and case reports. The journal
is published monthly by Blackwell Publishing. http://www.jim.se/

Contact: Annette Whibley
Blackwell Publishing Ltd.

Article URL: http://www.medicalnewstoday.com/medicalnews.php?newsid=56196