Anthrax in animals most commonly occurs following ingestion
of the organism, but can also occur by acquisition of the organism
in aerosols or via wounds. Herbivores are the most susceptible
to disease, while pigs and carnivores are relatively less susceptible.
Clinical presentations of anthrax in cattle:
- Peracute death is a common manifestation.
- Hemorrhage may or may not be externally evident in these
peracute cases.
- Subacute anthrax can also occur in cattle and small ruminants.
- fever and inappetence
- hematuria, hematochezia, peripheral edema
- splenomegaly
- respiratory distress
- behavioral changes and seizures (reflecting CNS edema and
hemorrhage)
- Blood in the body typically does not clot.
- Rigor mortis is often absent.
Anthrax in horses:
- Infection may present initially as colic and enteritis, followed
by development of edema, hemorrhage and death in 2-4 days.
Anthrax in pigs and dogs:
- Pigs and dogs generally have a more limited course of disease,
with gastroenteritis and pharyngeal edema. However, the pharyngeal
edema may lead to death by asphyxiation.
In endemic areas in the world, animals can be immunized with
a vaccine made from spores of an avirulent strain ("Stern
vaccine"). In incubator regions of some states in the
U.S. (e.g., the Dakotas), vaccination is also still commonly practiced
today. However, in other areas, vaccination is only by authority
of the State Veterinarian.
Diagnosis of anthrax in animals:
- A diagnosis is most often made by identification of the organism
in blood from an infected animal.
- Blood smears can be directly stained for the organism, or
the organism can be readily cultured.
- Necropsies should not be performed because of the risk of
inducing sporulation and spreading the organism.
- Blood should be collected with as little contact as possible
with the carcass (e.g., cutting off the tip of the ear or incising
into the coronary band) and then the carcass should be burned
thoroughly or buried deep and covered with quick lime (calcium
oxide).
- Quick lime acts to pull water out of the carcass and thereby
speed decomposition.
- In pigs, unlike cattle, organisms are often difficult to
find in peripheral blood smears.
- There are also fluorescent Ab-, ELISA- and PCR-based laboratory
tests available and an immunochromatographic rapid diagnosis
field test.
Examples of recent cases of anthrax in North America:
- In 1996, a cow died of anthrax in Ontario. Interestingly,
the owner reported that cows died of anthrax on the same farm
65 years ago and that recent excavations had been made in that
area. A similar series of events occurred on a farm in Nevada
in 2000 and ~1970.
- In 1997 and 1998, anthrax occurred among cattle in South
Dakota, New Mexico (associated with oil company drilling and
earth work) and the Northwest Territories of Canada.
- In 2000, over 150 livestock animals in North Dakota died
of anthrax. (This is a massive increase compared to only 24 cases
in N. Dakota between 1989-1999.)
- In 2000, over 150 livestock animals in North Dakota and 6
cows in Minnesota died or were euthanized because of anthrax.
- In this outbreak, 2 farmers slaughtered and ate one of the
affected cows. One of them developed intestinal anthrax and the
other cutaneous anthrax.
- In 2001-2002, anthrax occurred among animals in Texas, Nebraska
and South Dakota. The outbreak in Texas in 2001 killed more than
90% of the deer on one ranch. A South Dakota veterinarian who
necropsied a cow in 2002 developed cutaneous anthrax.
