Anaplasmosis
ANAPLASMOSIS PROTECTION
What is Anaplasmosis?
This is a disease of cattle caused by an organism called Anaplasma marginale.
This organism is a rickettsia, half way between the viruses and the bacteria.
It is susceptible to tetracyclines, unlike viruses. The disease, anaplasmosis,
is caused when the infected cattle react to the agent and remove their own
infected red blood cells. This reaction causes a severe anemia.
Which cattle are susceptible to infection with A. marginale?
All cattle are susceptible to infection by A. marginale. Also, deer,
elk, and other ruminants are susceptible to becoming infected and can act
as natural reservoirs of the agent. Cattle of any age can become infected;
however, young cattle do not become ill, as will be explained later.
How do cattle become infected with the anaplasmosis agent?
A number of ruminants such as cattle, deer, and elk can be carriers of the
anaplasmosis agent. These species can carry the agent all or most of their
lives and serve as a reservoir for infection of other animals. The transfer
of the agent from a carrier animal to a susceptible animal can occur by a
number of routes. One of the most common ways is via ticks. In California,
we have a number of ticks that transmit the anaplasmosis agent and are extremely
effective at passing the agent to new, susceptible hosts. Additionally, any
transmission of a small amount of blood from a carrier animal to a susceptible
animal can transmit anaplasmosis. So insects such as horse flies, are capable
of transmission. An even larger culprit in this type of transmission is man.
Ear-tagging instruments, tattoo tools, needles, ear implant tools, castrating
instruments, dehorning instruments, etc., can all easily transmit the agent.
So humans are also important in the spread of this disease.
What happens when a susceptible animal becomes infected?
If the animal is a calf under the age of 12 months, virtually nothing is noticed.
The calf undergoes an incubation period of about 45 to 90 days, has a very
mild illness, which is rarely noticed, and becomes a carrier for life. Cattle
that become infected between 1 and 2 years of age become ill after the incubation
period, with severity increasing with age. Cattle over 2 years of age become
very ill and approximately 50% die unless treated. The older the animal and
the better shape they are in—the sicker they get! Usually, once the cattle
become infected, and if they survive, stay infected for life. They are "immune
carriers"—they do not get sick, but act as a reservoir for other
susceptible animals. Therefore, being an infected carrier protects the animal
from becoming sick if re-infected.
What determines if a herd will have problems with anaplasmosis?
The location of the herd is the main factor determining whether or not problems
will occur. The cattle and deer that might be reservoirs and the ticks that
naturally transmit the disease are the primary factors. For example, herds
raised in the central valley of California on permanent pasture, with no ticks,
no deer, and no carrier cattle, there is essentially no risk of anaplasmosis.
These cattle are free of the disease, have no immunity (unless vaccinated),
and are totally susceptible to infection and disease. If these cattle are
introduced to foothill pastures, especially during a bad tick year, they will
become infected, get sick, and 50% will die if not treated. When cattle are
raised in the coastal foothills, Sierra foothills, and many mountain areas
of California, they become infected early in life, have no clinical disease
when infected (because they are young), and are "immune carriers".
If new, susceptible cattle come into these areas, they are at risk. If these
carrier cattle go to the valley pastures, they may act as sources of infection-especially
via blood transfer (dehorning instruments, ear taggers, horse fly transmission,
etc.). Many cattle herds are between these two extremes and it is common for
a percentage of the adult animals to become infected and ill every year. These
are herds that need to vaccinate routinely to prevent losses. It is common
for bulls that come from anaplasmosis-free areas to be very susceptible when
introduced to herds where anaplasmosis is common. Remember, when bulls become
infected and are successfully treated (do not die) they are often sterile
for many months.
What can I do to prevent anaplasmosis in my herd?
This depends on the risk of anaplasmosis in your operation. For those "valley"
herds, the only real risk is introduction of carrier cattle and transfer of
blood (dehorners, tattoo instruments, castration instruments, etc.) from the
new cattle to your native, susceptible animals. For foothill or mountain herds,
you have to be sure incoming cattle or bulls are from anaplasmosis areas or
have been vaccinated. For herds intermediate in risk, you will want to review
your vaccination program with your veterinarian.
This vaccine is very important. If you purchase bulls or heifers for replacements this fall, be sure these cattle are protected. If the cattle were vaccinated with the live vaccine (Anavac®) as calves and not fed tetracyclines in the feedlot, they will be immune carriers and safe from getting sick. If they were fed tetracyclines (a common procedure for bulls being grown in a feedlot), they will lose they immunity after 1-2 years if they do not become re-infected. If the cattle are over a year of age, be sure they were vaccinated with two doses of the killed investigational vaccine. They should be protected against becoming ill when naturally infected on your ranch.
The killed, investigational vaccine is available through the California
Wool Growers Association. Either contact use by phone at (916) 444-8122 for orders
or more information. This vaccine costs $7.50/dose for 10 dose vials and $6.50/dose
for 50 dose vials.
As you see form the brief discussion, anaplasmosis is a very complicated disease
and the need to vaccinate will vary from herd to herd.