Apr. 05, 2001 (United Press International via COMTEX) -- As the number of
animals facing slaughter in Britain as a result of foot-and-mouth disease passes
the one million mark, United Press International presents an in-depth multipart
survey on the causes and likely implications of the epidemic, the worst disaster
to hit British agriculture in modern times. Here, Science Reporter Kurt Samson
explains what foot-and-mouth disease is, and why it is so dangerous.
Foot-and-mouth disease is a highly contagious disease caused by the picorna
virus. It was last reported in 1929 in the United States, 1952 in Canada and
1954 in Mexico. In Britain there was a large outbreak in 1967 and another small
one in 1981. After each outbreak, Britain was able to eradicate the disease.
The disease can be transmitted from animal to animal, or via contaminated
personnel, equipment or feed. Wind may spread the virus over long distances.
Once breathed in by animals, the virus replicates and gains access to the
bloodstream where it spreads to the mouth, feet, stomach and teats as well as
the heart muscle, especially in younger animals. Infected animals are highly
contagious even before they show symptoms -- an incubation period that can last
for up to three weeks.
Nearly any animal exposed to foot-and-mouth will develop the infection, though
the death rate in adult animals is only about 5 percent. Three-quarters of young
animals do not, however, survive. Surviving animals can carry the virus for up
to two years without showing any symptoms. The virus is resistant to cold
temperatures and survives even freezing, but it can be killed by acidic
substances of less than PH 5, such as beer, milk or tomato juice.
Cloven-hoofed livestock including cattle, pigs, sheep and goats as well as
several wild animals (deer, water buffaloes, bears, antelopes, llamas, camels,
giraffes, elephants, rats, hedgehogs) of all ages and sexes are susceptible to
infection. Humans in very rare cases may develop very mild forms of disease.
Horses do not get the disease.
Occasionally, the virus is imported to disease-free countries by contaminated
frozen meat or garbage. Several outbreaks could be traced to consumption by
livestock of uncooked waste or swill from ships or airplanes originating from
infected countries. Even contaminated medicines such as vaccines against hog
cholera or insufficiently inactivated foot-and-mouth vaccines have been a source
of infection in the past.
The highest risk of entry of the disease is through the import of susceptible
live animals, and contaminated meat or dairy products from infected countries.
The virus can survive for long periods in a range of fresh, partially cooked,
cured and smoked meats and in inadequately pasteurized dairy products. These
could be brought in with passengers on aircraft and ships, through the mail or
on fishing vessels or yachts.
The virus can survive for relatively long periods of time in the air, in food
and garbage, and even in hides, hair, and wool, so draconian measures have to be
taken to control the disease. A diagnosis of the affected animals must be made
quickly and the area quarantined, after which all infected or susceptible
animals in the area are slaughtered and their carcasses burned. Other
contaminated objects are cleaned and disinfected, and the farm or other
quarantined area is left uninhabited for several months.
According to Alex Donaldson, director of the British-based World Reference
Laboratory for Foot-and-Mouth Disease, scientists in that country are unsure
about the source of the current outbreak. The most likely scenario is that it
was brought into the country illegally in an animal product. The Pan-Asian type
O virus strain associated with the British cases has a wide geographical
distribution, particularly in the Middle and Far East, though specific links
have not been established.
The outbreak began with 24 suspected cases in pigs at an Essex slaughter house
on Feb. 19. By April 4, the number of cases had jumped to more than 1000.
As of April 3, there had also been 10 outbreaks in the Netherlands; two in
France; one in Scotland; and one in Ireland. Argentina has had 75 confirmed
outbreaks, Brazil had 54 and Peru reported 44 outbreaks. In the Middle East,
Saudi Arabia has reported 2,000 outbreaks, Iran 455 outbreaks and 22 reported in
Kuwait.
Outbreaks are determined by new incidence of the disease in a given geographic
area. The estimated number of infected and susceptible animals that must be
destroyed in Britain now totals 1,010,000.
A major contributing factor to foot-and-mouth becoming widespread in Britain was
the delayed reporting of disease on the source farm. By the time the disease was
confirmed, infection had been transmitted through markets, primarily by sheep
that were carrying the virus but not yet showing symptoms.
In cattle, the primary sites of infection are mainly the nostrils, following
inhalation of virus-laden air. After an incubation period of two to 21 days (in
most cases three to five days), infected animals develop fever, depression,
nasal discharge and anorexia.
Blisters may appear on the muzzle, teats, udder, pili of the rumen,
inter-digital area and coronary band. They contain a straw-colored fluid, are
painful and cause anorexia and lameness in affected cattle. Two or three days
after appearance, the blisters rupture, leaving denuded areas, erosions and
painful ulcers.
Frequently, the healing is delayed by a secondary bacterial infection of the
wounds. Severe forms of mastitis, bronchopneumonia and lameness may occur
subsequent to the initial viral infection. Miscarriage and weight loss as well
as a drastic decline of milk production are common. Calves up to six months and
piglets up to two months frequently develop fatal degeneration of the heart
muscle and die within a few days without showing any other clinical signs.
Inactivated vaccines have been successfully used in many parts of the world,
however development of effective vaccines has helped control epidemics but has
not eliminated the disease.
Although protected against disease, vaccinated animals are not totally resistant
and can still become infected and infectious. Resistance falls fairly quickly,
so animals must be revaccinated at regular intervals (four to six months) to
maintain immunity.
The disease is endemic to Asia, Africa, parts of Europe, the Middle East and
South America. The virus strain that recently arrived in Britain (serotype 0) is
native to the Indian subcontinent.
Trans-boundary diseases often originate in the Middle East and Asia. In 1999,
foot-and-mouth disease caused extensive cattle losses in Iraq. Turkey and Iran
play an essential role in the fight against cross-border diseases in the Middle
East, because viruses frequently pass through these two countries and then
threaten Europe, according to health officials.
Globally, the foot-and-mouth disease situation deteriorated in 2000 with the
appearance of cases in Japan, South Korea, South Africa and in some countries in
South America, which were free of the disease until very recently. Countries
affected by outbreaks in the past 12 months include Britain, France, the
Netherlands, Butan, Brazil, Columbia, Egypt, Georgia, Japan, Kazakhstan, Korea,
Kuwait, Malawi, Malaysia, Mongolia, Namibia, Russia, South Africa, Taipei,
Tajikstan, Uruguay and Zambia. The last major outbreak of the disease in the
15-nation European Union was in Greece last year.
