One method to maintain communication and educational efforts to our community is the release of newsletters. With recent development of internet-based information and mass media, it is important to use these communication methods to relate time-based information to our constituents instead of traditional printed materials.. Because the time sensitive information due to recent rains and high incidence of mosquitoes in Hopkins County, I decided to share this information with our general public and specially with those raising beef cattle. Anaplasmosis is an infectious disease of cattle that causes destruction of red blood cells. The disease is caused by a minute para site, Anaplasma marginale, found in the red blood cells of infected cattle . It can be transmitted from infected animals to healthy animals by insects or by surgical instruments. Anaplasmosis can be divided into four stages: incubation, developmental, convalescent, and carrier. These stages and the symptoms associated with them are described below.
The incubation stage begins with the original infection with A. marginale and lasts until 1 percent of the animal’s red blood cells (RBCs) are infected . The average incubation stage ranges from 3 to 8 weeks, but wide variations have been documented. Most variation is directly related to the numb er of organisms introduced into the animal. After gaining entry into a susceptible animal, the anaplasma para site slowly reproduces in the animal’s blood during the incubation phase. During this period the animal remains healthy and shows no signs of being infected. Finally, after the para site has reproduced many times and established itself in the RBCs of the animal, the body attempts to destroy the parasite.
During the developmental stage, which normally lasts from 4 to 9 days, most of the characteristic signs of anaplasmosis appear. Clinical signs begin to be expressed about half- way through this phase. As the infected animal’s body destroys the para site, RBCs are destroyed as well. When a substantial loss of RBCs has occurred, the animal will show signs of clinical anemia. The body temperature will comm only rise to 104.o to 107.o F (40.o to 41.o C), and a rapid decrease in milk production will occur in lactating cows.Cattle producers first notice the anemic, anaplasmosis-infected animal when it becomes weak and lags behind the herd. It refuses to eat or drink water. The skin becomes pale around the eyes and on the muzzle, lips, and teats. Later, the animal may show constipation, excitement, rapid weight loss, and yellow-tinged skin. The animal may fall or lie down and be unable to rise. Affected cattle either die or begin a recovery 1 to 4 days after the first signs of the disease. As a general rule, unless infected cattle can be detected during the early developmental stage, they should not be treated. There are two primary reasons for this practice. First, if the animal is forced to move or becomes excited, it may die of anoxia (lack of oxygen in the animal’s system). Second, antibiotic treatments do little or nothing to affect the outcome of the disease when given during the late developmental or convalescent stage.
Cattle that survive the clinical disease lose weight, abort calves, and recover slowly over a 2- or 3-month period. This is known as the convalescent stage, which lasts until normal blood values return. This stage is differentiated from the developmental stage by an increase in the production of RBCs (erythropoiesis) in the peripheral blood, shown in an increase in hemoglobin levels and high total white blood cell counts, among other characteristics. Death losses normally occur during the late developmental stage or early convalescent stage. Cattle of all ages may become infected with anaplasmosis, but the severity of illness increases with age. Calves under 6 months of age seldom show enough signs to indicate that they are infected. Cattle 6 months to 3 years of age become increasingly ill, and more death s occur with advancing age. After 3 years of age, 30 to 50 percent of cattle with clinical anaplasmosis die if untreated. Unless adequately medicated, cattle that recover from anaplasmosis remain reservoirs (carriers) of the disease for the rest of their lives.
During the carrier stage, an animal will not exhibit any clinical signs associated with the persistent low-level A. marginale infection. Nevertheless, the blood from these recovered animals will cause anaplasmosis if introduced into susceptible cattle . Anaplasmosis outbreaks are related to the lack of a control program, the ratio between anaplasmosis carriers and susceptible animals in the herd, and the amount of vector transmission. An increase in the ratio of carriers to susceptible animals or an increase in vector transmission can influence the severity of an outbreak. With these factors in mind, the producer needs to consider reducing vector transmission, developing control programs to prevent outbreaks, eliminating the carrier state , and using treatment or management options available to stop an outbreak of anaplasmosis. Knowing how to interpret anaplasmosis outbreaks can yield valuable information on necessary changes in management.
Outbreaks occurring during the vector season would indicate infection of susceptible cattle and acute outbreaks of anaplasmosis. If this situation occurs, preventative measures, such as vaccinations or antibiotic therapy as outlined in later sections, should be implemented. If outbreaks occur during the winter months, they are due not to recent infection of the susceptible cattle but to stress, which can lead to expression of the disease in infected cattle. In this situation, vaccination would not prevent further outbreaks during this non-vector season. Vaccination works to prevent acute expression of the disease upon infection during the initial exposure. It does not prevent infection or the development of a carrier animal. Antibiotic therapy can be used to control this type of outbreak as described later in the section “Control Programs for Anaplasmosis.” An additional strategy is preventing stress in susceptible cattle . Nutrition and environmental stress are two areas that must be managed closely in suspect herds. An increase in outbreaks during a non-vector season would indicate that stress is a key factor in the expression of symptoms.
What can you do? Get familiar with clinical signs of anaplasmosis and develop an efficient relationship with your veterinarian. Recent regulations related to drug usage limits its availability to valid veterinarian- patient relationships. During the veterinarian visit, share your observations and ask about the possibility of anaplasmosis in your herd.
For more information on this or any other agricultural topic please contact the Hopkins County Extension Office at 903-885-3443 or email me at [email protected]
Mario Villarino DVM, Ph.D.
Hopkins County Extension Agent for Ag and NR
1200B Houston Street
Sulphur Springs, Texas 75482