New emerging diseases in U.S. only a matter of time, expert says

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Apr 01, 2003

African Horse Sickness, Hendra and Glanders are diseases Dr. Corrie Brown hopes to avoid in her lifetime.

Although none of the diseases has crossed U.S. borders, each remains a plausible emerging disease threat.

"They're diseases you hope you never see, but if you do, you darn well better be able to diagnose them. The most worrisome disease is the one that enters next," says Brown, a professor at the University of Georgia.

Let West Nile Virus be a reminder. Prior to 1999, the virus wasn't on this country's radar screen. "Who would've expected West Nile to spread the way it did? West Nile was very, very low on the list of possible introductions.

"The amount of damage we will suffer from an introduced disease is directly related to how quickly we recognize it and are able to eradicate it," says Brown.

Brown gave a presentation, "Foreign Animal Diseases with Equine Potential," at the most recent American Association of Equine Practitioners convention in Orlando. She highlighted viable disease occurrences and protective measures equine practitioners can take.

Potential threats include:

* African Horse Sickness

African Horse Sickness (AHS) virus, an orbivirus, topped her list. Rooted in Africa but known to make incursions in new areas, the acute systemic illness, transmitted through Culicoides insects, primarily affects horses. Mortality rate is 70 to 95 percent. Clinical signs include respiratory distress, edema, colic and hydropericardium hemorrhage.

AHS-infected insects could easily arrive within the states, says Brown, due to high rates of international travel. As a precaution, Brown recommends vaccination as well as eliminating all Culicoides insects.

Awareness of such diseases alone goes a long way toward prevention, adds Brown.

"If African Horse Sickness, for example, is introduced into the U.S. and no one is thinking about African Horse Sickness, then it's not going to get diagnosed. It's going to spread, and we're going to have a heck of a time getting rid of it. Whereas, if we're already thinking about it, then we're going to diagnose the first case, then get rid of it and it won't get established in the insect population."

* Glanders

This historical contagious disease was initially developed as a bioweapon during World War I to infect horses of enemy troops. Eradicated from the U.S. in 1937, the disease, caused by the bacteria Burkholderia mallei, is currently restricted to Asia and Eastern Europe.

Animals present with fever and then signs referable to point of entry. In non-endemic areas, the disease can be mistaken for strangles, rhodococcal pneumonia or ulcerative lymphangitis.

No treatment is recommended for the disease.

* Hendra

A new paramyxovirus that emerged in Australia in 1994, Hendra is spread by the fruit bat. The disease presents similar in horses, cats and guinea pigs, although its primary targets are humans and horses. Clinical signs can resemble pneumonia. Probability of U.S. entry is minimal, reports Brown. That said, she notes that researchers know less than 10 percent of all bacteria and viruses present in all animal species. Normal flora in one species when transmitted to another may cause an emerging disease.

* Trypansomal diseases

Dourine is a fatal equine venereal disease present worldwide that causes swelling of external genitalia. It was eradicated from the United States in 1949. The clinical disease invades mucous membranes, migrates to the reproductive tract and causes vaginal discharge, abortion and skin plaques. Treatment is not usually undertaken.

* Surra

Transmitted by tabanid flies, the disease affects equine, cattle, buffalo and camels in Asia, Africa and South America.

African animal trypanosomiasis, or Nagana, causes anemia, edema and fever and is transmitted by the Tsetse fly.

* Venezuelan equine encephalitis

Of Eastern, Western and Venezuelan equine encephalitis, only VEE is a foreign animal disease. Although it last appeared in the United States in 1971, it recently cropped up in northern South America and Mexico, worrying scientists. The disease presents with neurological dysfunction. Vaccines are available.

A different world

The catchphrase "globalization" has secured its place in the world arena of foreign animal diseases, and America can't afford to be a stranger to it.

"Over the last 20 years, the world has become globalized," Brown says. "There's a tremendous amount of trade and traffic. The possibilities for introduction of foreign animal diseases now ­ it's not a matter of if, it's a matter of when."

She adds, "There are two ways a veterinarian can become 'famous' when a foreign animal disease enters the neighborhood. One way is to diagnose it; the other way is to miss it."