That is a big order to fill when attempting
to answer a question such as this. However, these three diseases
are on the minds of a good many people, especially horsemen,
livestock producers and government regulatory officials,
as well as those individuals and organizations that are involved
with research dealing with these conditions.
So, to begin to answer the question, let’s first
deal with the West Nile Virus.
WEST NILE VIRUS ENCEPHALITIS
According to the literature I have read, the West Nile
Virus (WNV) was first isolated in 1937 in Uganda from cases
of human and equine encephalitis. At the same time it was
also recovered from some species of birds which had died
from the virus infection. Since that time the virus has
been endemic in Europe, Africa and some areas of Asia.
The Japanese B virus is related to WNV. The first outbreak
of Japanese B encephalitis was reported from Japan in 1871,
but it attracted very little attention until 1924, when
another epidemic occurred in Japan involving more than
6,000 persons, of which 3,797 died. In 1940, scientists
discovered that certain species of mosquitoes were the
vectors of this virus.
In late July, 1999, WNV made its appearance in New York
City and Long Island, primarily in Suffolk County, New
York. Its appearance was heralded by a rash of deaths involving
crows, blue jays, sea gulls and some red-tailed hawks.
There were reported cases of human and equine encephalitis.
Blood and tissue samples of affected birds, horses and
humans were analyzed and tested at state and federal laboratories.
WNV was established as being the causative agent.
How did the virus get here? We know the virus is transmitted
by mosquitoes and was probably brought here on a migrating
bird or carried on a human being. Once established, the
infection is spread by migrating birds, which become infected
by the carrier mosquitoes.
Four states were involved in the WNV outbreak in 1999.
They were New York (largely in New York City and Long Island),
New Jersey, Maryland and Connecticut.
In this outbreak there were 62 human cases, of which there
were seven fatalities. Twenty-five horses were diagnosed
on Long Island with WNV encephalitis, with a 32% fatality
rate.
The virus successfully overwintered in the mosquito population
and spread in the year 2000, so it is now found in 12 eastern
states and the District of Columbia. It was diagnosed in
cases occurring as far south as northern North Carolina,
north in Vermont and New Hampshire and as far west as Erie,
Pennsylvania.
There were 59 equine cases of WNV documented in the year
2000 in seven states. Of these, 39% were put down or died.
In addition, it is known that bats, a rabbit, chipmunk
and skunk were also infected.
WNV accounted for over 100,000 bird deaths, of which some
16,000 were tested after death for evidence of the virus.
Crows are especially susceptible. In fact, 96 to 98% of
infected birds will die in four to five days following
exposure to the virus. The presence of dead crows is often
indicative of the presence of WNV. The infected crow will
shed a lot of the virus in its feces, and finding an average
of 1.5 to 2 dead crows per square mile is indicative of
the presence of WNV in the crow population and, therefore,
in the mosquito population.
So what is in store for the year 2001 as far as WNV is
concerned? The virus could spread west, north, and south
of its present boundaries. Dr. Peter Timoney, director
of the Gluck Equine Research Center at the University of
Kentucky, states “It is a virus that can survive
and adapt to a wide spectrum of species of birds and mammals.
There is no room for complacency about this virus. You
don’t want to panic people but you do need to educate
them.”
So what should you look for in an affected horse? You
could be suspicious of WNV if the animal shows a staggering,
wobbly gait, or if it is unable to stand or has a paralysis
of one or more of its legs. In addition, any horse that
shows listlessness, depression, paralysis of the lower
lip and inability to eat should be a suspect. Any sudden
or acute death of a horse should be also viewed as possible
WNV disease.
If the virus continues to journey southward along the
eastern coastal states, it will soon reach areas where
mosquitoes are active year round. The incidence of this
disease could then take on a whole new aspect.
Enter into the picture the Asian Tiger mosquito. It entered
the U.S. at Houston, Texas, from Asia in a shipment of
old tires, and it very quickly became at home. It is a
known resident in 21 of the 50 states. I have been told
we cannot get rid of our own old tires, so why did we have
to import some and bring this rascal along with ‘em?
Anyway, the Asian Tiger mosquito is a dry weather breeder.
It breeds and survives nicely in drought conditions. At
present it is not known to harbor the WNV; however, it
is known to be a host to many other viruses. If it should
become a carrier of WNV, the whole southern area of the
U.S., including many hot and dry places, could become at
risk to this form of encephalitis.
Another mosquito which has recently been introduced to
northeastern America is Iedes japonicus, which comes to
us from the Far East. This mosquito has experimentally
been infected with WNV and therefore has the potential
to become naturally infected, which would make it another
vector in the spread of the disease.
So what can be done to halt or impede the spread of this
disease? Mosquito control programs are the best solution
to date. People should be on the lookout for mosquito breeding
areas and when found, they should be eliminated or treated
if at all possible. Every effort should be made to eliminate
breeding sites of mosquitoes.
Development of a vaccine is being undertaken, but officials
believe a vaccine will not be available until the end of
the year 2001.
This new virus may very well be here to stay, and it will
be a problem that equine breeders and owners will have
to face now and in the future, much as they have had to
deal with the eastern and western equine encephalitis viruses.
Now, since we’ve discussed a relative newcomer on
the stage, let’s go on and check out an old-timer
which has staged a reappearance and is causing great financial
repercussions for the governments of the United Kingdom
and many countries in Europe.
FOOT AND MOUTH DISEASE
Foot and mouth disease (FMD) is an acute infection whereupon
blisters or vesicles develop on the mucous membranes of
the mouth and on the skin of the udder and teats.
Primarily it is a disease of cattle, hogs, sheep, goats
and other cloven-hooved animals. However, other animals
and, very, very rarely, man may become infected secondarily.
It is the most highly contagious disease to which cattle
and swine can be exposed.
The history of FMD is shrouded in the mists of time. For
some past centuries it was known and recorded in Central
Europe, but its infectious nature was not recognized until
1764. It took another century to develop its etiological
nature. An outbreak recorded in 1911 in Central Europe
affected 3,366,369 cattle, 1,602,927 sheep, 2,555,731 hogs,
and 53,674 goats, or about one out of every seven animals
in that area.
It is interesting to note that since 1850 to 1933, FMD
has appeared in the United States on twelve different occasions.
In 1870 the disease spread into New England and New York
State. It was thought to have come from Scotland, by way
of Canada, and was brought under control in a short time.
In 1880, FMD was discovered in three lots of imported cattle,
and it was controlled before it could spread further. In
1884, a third outbreak was discovered in Portland, Maine,
but again was brought under control before spreading. All
three of these epidemics were caused by the importation
of diseased cattle. Soon after the last outbreak, the U.S.
Department of Agriculture was formed, and strict inspection
measures on imported cattle have been enforced.
The fourth outbreak of FMD, in 1902, appeared at Chelsea,
Massachusetts, and spread through New England. This onset
was due to contaminated cowpox virus which was brought
in from Japan for the production of smallpox vaccine. Most
people do not know this, but the cowpox virus was inoculated
by scarification into the skin of calves. This, in turn,
was harvested and the product was the smallpox vaccine
used on humans to prevent smallpox. 4,712 cattle were slaughtered,
as well as several hundred sheep and goats. In November
of 1908, the fifth outbreak occurred in Michigan and spread
to Maryland, Pennsylvania, and New York. This again was
caused by contaminated vaccine brought in from Japan for
the production of the smallpox vaccine. The calves were
infected, as well as the vaccine which was produced. A
second firm purchased some of the contaminated vaccine
and in turn infected its calves. These calves were sold
on the open market and infected other cattle. One hundred
fifty-seven farms were infected, and 3,636 animals were
slaughtered, valued at $90,033. The government recalled
all of the contaminated vaccine. Since that time, the Federal
Government, through the United States Public Health Service,
has assumed control of vaccines and health products for
humans, while the Bureau of Animal Industry does likewise
for the same classes of products bound for veterinary use.
In October 1914, the most extensive and costly outbreak
of FMD broke out near Niles, Michigan. This was the sixth
recorded, and the virus probably found its way there from
South America in or on some merchandise.
The Chicago Stock Yards became infected, and, to make
matters worse, the National Dairy Show was being held there
at the time. A plant manufacturing hog cholera virus was
also infected, and one lot of contaminated hog cholera
virus was released for vaccination purposes. From Iowa
to Massachusetts, the District of Columbia and twenty–two
states were affected with 3,556 herds being slaughtered
at a cost of over $6,000,000.
The seventh outbreak occurred around the San Francisco
Bay area, caused by garbage on a ship from the Orient which
was fed to hogs. This took place in 1924, and from the
Bay area, it quickly spread in six months to 16 counties
in California. 58,791 head of cattle were destroyed, along
with an unknown number of hogs, sheep and goats.
An incident during this outbreak quickly caught the public’s
attention. It was called the “border war” between
Arizona and California. Arizona prohibited automobiles
from coming into the state from California. Cars and tourists
were stranded at the border, until at one time 700 people
and 200 cars were waiting to get across the border into
Arizona. In 1924, that was a lot of people and autos! They
were finally allowed to proceed on their way after thorough
disinfection of people, autos and baggage.
In September of 1924, the eighth outbreak appeared in
Texas. It was not related to the California onset, but
was thought to have been brought in by crewmen from several
ships that came from infected ports, who were taking on
cattle for food. The outbreak was brought under control
in 30 days by the complete and immediate slaughter of 148
herds.
The next year, 1925, the same set of circumstances led
to the ninth outbreak, again in Texas. In this instance
153 infected herds and 848 exposed herds were slaughtered
and the outbreak was completely controlled.
Infected garbage from a ship from South America, which
was fed to hogs, caused the tenth outbreak, again in California.
It was limited to five herds of hogs. This outbreak lasted
from January to March, 1929. Several new methods were employed
to control this episode along with the slaughter of infected
and exposed herds.
Outbreak number eleven happened in April of 1932, again
in Southern California. This one involved 37 herds of hogs,
and the source of the virus was, again, infected garbage
from ships from the Orient. In three weeks the outbreak
was under control.
The last outbreak of FMD happened in 1933. It was a small
incident in some hogs in San Diego, California. The source
of infection, once more, was contaminated garbage from
ships which was fed to the pigs.
FMD is caused by a virus which has a wonderful propensity
to survive under many conditions and retain its highly
infectious nature. There are at least seven different types
and many sub-types of the virus. Immunity to one type does
not necessarily provide immunity to any of the other types.
It has been found that the virus may remain alive and
lethal for six months if kept in cool, moist surroundings
at temperatures from 3.5 to 5.5 degrees Celsius. It has
been known to stay alive and be active on an infected premise
for 283 days and on another for 345 days. It is very resistant
to some disinfectants, but heating at 55 degrees Celsius
for 15 minutes will destroy it.
The virus causing foot and mouth disease in cloven-hooved
animals is closely related to those which cause vesicular
stomatitis in horses and vesicular exanthema in hogs. The
three viruses can only be identified by certain pathogenic
and immunologic properties.
How is this virus spread? Recently, APHIS has printed
a bulletin on foot and mouth disease. They put it very
well, and the following is a direct quote from the article:
Do humans contract this disease? The answer is yes, but
the incidence is extremely rare. A researcher in this field,
Trautwein, in 1932, could find only three human cases where
symptoms of the disease in man were verified by animal
inoculation. This was reported in Arch.Ohren–USW.Heilk.
1932, 130–249. So, for all practical experience,
man does not have to worry about contracting this ailment.
Today it is estimated that a third of England’s
farms will lose livestock to the disease and slaughter
as the country tries to control and contain FMD. The loss
in dollars is simply staggering and it will be felt by
the nation and its people for years to come.
The same can be said for the countries of Western Europe
where outbreaks of FMD have been discovered and efforts
are underway by their respective governments to contain
and eradicate the disease.
To prevent the introduction of FMD into the United States,
the USDA has imposed severe restrictions on the importation
of any livestock, livestock products, or even pets from
countries affected with FMD. Travelers coming from these
areas must submit themselves and their baggage to certain
procedures upon arriving in the U.S.A.
To have FMD get a foothold in our livestock industry would
produce devastating social and economic problems. Look
at what is happening in England and Western Europe today.
BOVINE SPONGIFORM ENCEPHALOPATHY OR BSE FOR SHORT
Recently two very good papers written about BSE were published
in The Veterinary Practice News. One in the March 2001
issue written by John B. Herrick, D.V.M. and the second
written by Mr. Ron Bast, was published in the April 2001
issue. Both articles are excellent in their discussion
of BSE and it is from the material presented in these issues
that I will try to give you an accurate insight into the
disease or condition. This is so you might understand it
and not be carried away by media-induced panic on the subject.
I personally, as well as the authors of these papers,
do not believe the term coined by the media as “mad
cow disease” is at all accurate or, indeed, appropriate.
During my years of large animal practice I have seen many “mad” cows.
I’ll describe them for you. They are up on their
feet, their heads are held high, ears are pointed forward,
eyes are wide open and focused right on you. Their nostrils
are dilated and the nose is thrust somewhat forward, which
gives you the impression that they are “looking down
their nose at you.” And they are! These cows are
very angry and at this stage of the game could be called
a “mad cow.” If you give them half a chance
they will “clean your plow.”
According to both of these authors and other descriptions
I have read about how an afflicted cow behaves, a different
picture begins to emerge. The affected cow will often show
incoordination, difficulty in rising. She will struggle
to get onto her feet and show anxiety and depression. Affected
animals will exhibit loss of body condition and may display
changes in temperament, such as nervousness or aggression.
Many of these animals will continue to eat, as their appetites
do not seem to be impaired.
BSE first appeared in Great Britain in 1986. It is a fatal
degenerative disease of the central nervous system. In
November, 2000 new cases were reported in Germany, Spain
and France. Ninety-two cases were reported in 2000 by the
French government. According to Mr. Bast, BSE has claimed
178,000 cattle worldwide since 1986 and 95% of all cases
to date have been from the United Kingdom.
BSE is classified as a spongiform disease. Two other similar
diseases are scrapie in sheep and Creutzfeldt-Jakob disease
(nv CJD) in humans.
In 1982 researchers in California described the cause
of scrapie in sheep to be a protein substance which they
called a prion. These prions are small protein-like particles
which contain no nucleic acid, no DNA or RNA. They are
very resistant to destruction or inactivation by most procedures
that change nucleic acid, and the theory is they may be
a new kind of contagious disease producer. These prions
can withstand autoclaving and the one causing BSE can withstand
rendering, doses of radiation and ultraviolet light.
Let’s put this all on a level plane for you to understand.
Our bodies have a protein called PrP which is used in nerve
cells. If untold numbers of these PrP particles gather
together, they form plaque in the brain. According to Dr.
Herrick, some scientists believe that the prion attaches
itself to the healthy PrP and turns it into another prion.
This process, it is believed, repeats itself until a large
mass of the protein material is formed in the brain, thus
causing the lesions which are found there. This also will
account for the “spongy” feeling of the tissue
and will cause the symptoms as seen in transmissible BSE.
Great Britain’s BSE epidemic apparently was caused
by feeding cattle contaminated meat and bone meal. Remember,
the prions are not destroyed by rendering. An oral dose
of one-half to one gram of infected brain tissue appears
to be sufficient to infect the susceptible cow.
Apparently humans can develop (v CJD) by eating the contaminated
meat from these infected cattle. No cases of (v CJD), the
human form of BSE, have been reported among veterinarians
or other people who have worked and been in contact with
BSE cattle in Great Britain.
To date, 85 human deaths have been attributed to the disease
in Great Britain. This number may go higher, as it is known
the disease or condition may be harbored in the body for
as long as ten years before symptoms of the condition appear.
It appears BSE, thus, has been curtailed but at a tremendous
price. Beef consumption in the U.K. has dropped over 50%.
The diagnosis of the disease in the live animal or human
is extremely difficult. No test procedures exist at this
time to diagnose the disease before the victim dies. This
may change, however, since British scientists have announced
in February that they have identified a possible BSE marker
in immature blood cells. Boehringer-Ingeheim has recently
petitioned the European Union for a global patent for a
blood test that detects the disease in living cattle. According
to a Reuters report, the test could be in use by late summer
2001.
So what are the U.S. government agencies doing to prevent
us from getting BSE established in our cattle?
In 1997 the FDA issued an order banning the feeding of
animal protein to ruminants. This includes meat meal, bone
meal and blood meal. By-products from poultry, such as
feather meal and poultry-by-product meal, can still be
used.
In 1989, the USDA placed import bans on live ruminants
and ruminant products from BSE infected nations. U.S. herds
are constantly monitored for signs of the disease. APHIS
has tested the brains of 12,000 slaughtered cattle nationwide.
This is more than five times the numbers recommended by
the international BSE surveillance standards. None of the
tests showed any sign of BSE.
No cases of BSE have ever been reported in the U.S. At
the moment our cattle are free of the disease, and our
beef is perfectly safe to eat from the consumer’s
standpoint. With vigilance and cooperation by all who are
concerned with the cattle industry, the health of our beef
business should be assured.
Recently, as most of you readers may know, the USDA seized
two flocks of Belgian sheep from their owners in Vermont.
Tests had shown that four of these animals were infected
with scrapie, the sheep spongiform disease.
They were sent to the Federal Lab at Ames, Iowa, to be
slaughtered, their brains tested for evidence of the disease
and their remains destroyed by being immersed in vats containing
boiling lye.
Remember, the prions which cause this type of disease
can withstand ordinary cooking and rendering procedures.
Results of the tests may not be known for a period of
time, maybe as long as two to three years, since the brain
material from the sheep is inoculated into mice for study.
IN SUMMARY
Now, after reading these articles about three very important
diseases of livestock, I want you to take a moment and
give them some thought.
You, as horsemen and women will be directly concerned
with the West Nile Virus as it fans out from its foothold
in twelve states along the eastern seacoast. It has the
potential to become a major health problem for humans,
the horse industry and wildlife. Do what you can to suppress
the mosquito populations by removing their breeding areas.
Keep informed and abreast of this disease as it continues
on its course.
At the present time we do not have either Foot and Mouth
Disease or so-called “Mad Cow Disease”in the
United States, Canada or Mexico. Be informed of the facts
concerning these maladies. I have tried to do this for
you. Do not be swayed by any media information which may
tend to sensationalize or over-dramatize these conditions
in order to create news.
Many of you readers may travel in the near future to countries
which are engaged in a struggle against one or both of
these diseases. Be careful and please do not make light
of rules and regulations that you must observe when returning
to this country. Government importation rules, regulations
and requirements for importation of livestock, livestock
products and even your re-entry into the U.S. are all designed
to protect the livelihood, health and welfare of all of
us. They protect our very way of life, as we are a livestock
producing nation, and its partial or complete loss would
be absolutely devastating to our economy and our way of
life.
Not all people agree with this philosophy. I leave you
with this excerpt from an editor’s editorial which
appeared in the April 15, 2001, issue of the Sioux City
Journal:
“When we read a Reuters News Service article quoting
the president of the People for the Ethical Treatment of
Animals (PETA) as saying that she hoped the dreaded foot
and mouth disease, currently devastating the livestock
industry and economy in Europe, would strike here, we were
left with a strong feeling of dismay and fear.
We were dismayed that any individual would wish such a
curse on any animal, let alone the livestock economy. Fear
manifested itself when we realized that an act of animal
terrorism, something PETA is known to support, could bring
the disease here.
‘If that hideousness came here, it wouldn’t
be any more hideous for the animals—they are all
bound for a ghastly death anyway. But it would wake up
consumers,’ said PETA co-founder and president Ingrid
Newkirk. ‘I openly hope that it comes here. It will
bring economic harm only for those who profit from giving
people heart attacks and giving animals a concentration
camp-like existence. It would be good for animals, good
for human health and good for the environment.’
Those words go beyond the scope of human dignity. Any
environmentalist or animal rights enthusiast should condemn
those comments.”
(Editor’s Note: Doc tells us that his chronicle
of outbreaks of Foot and Mouth in the United States was
drawn from Diseases Transmitted from Animals to Man, by
Thomas G. Hall, 3rd edition, 1947. As many of you might
have noted in recent weeks, there have been several stories
in our daily papers that list 1929 as the “most recent” oubreak.
That obviously isn’t correct. There were a couple
of incidents after that one. This 1929 thing, once printed,
apparently became the “gospel” for feature
writers. Most feature writers and wire service editors
are not veterinarians with a penchant for “checking
out the facts.”)
