Beef Tips- Anaplasmosis by Mario Villarino
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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 tra nsmitted from infected animals to healthy animals byinsects or by surgical instru ments. Anaplasmosis can be divided into four stages: incubation, developmental,convalescent, and carrier. These stages and the symp- toms associated with them are described below.
The incub atio n stage begins with the original infection with A. marginale and lasts until 1 percent of theanimal’s red blood cells (RBCs) are infected . The average incubation stage ranges from 3 to 8 weeks, but widevariations have been docum ented. Most variation is directly related to the numb er of organisms introd ucedinto the animal. After gaining entry into a susceptible ani- mal, the anaplasma para site slowly repr oduces inthe animal’s blood dur ing the incubation pha se. Dur ing this period the animal remains healthy and shows nosigns of being infected . Finally, after the para site has repr oduced many times and estab lished itself in the RBCsof the animal, the body atte mpts to destroy the parasite. Dur ing the develop m en tal stage, which normallylasts from 4 to 9 days, most of the character istic signs of anaplasmosis appear .Clinical signs begin to beexpressed abo ut half- way through this pha se. As the infected animal’s body destroys the para site, RBCs aredestroyed as well. When a substa ntial loss of RBCs has occurr ed, the animal will show signs of clinicalanemia. The body temperature will comm only rise to 104o to 107o F (40o to 41o C), and a rapid decrease inmilk production will occur in lactat ing cows.Cattle producers first notice the anemic, anaplasmosis-infectedanimal when it becomes weak and lags behind the herd. It refuses to eat or drink water. The skin becomes pale aro und the eyesand on the muzzle, lips, and teats. Later, the animal may show constipation, excite ment, rapid weight loss, and yellow- tinged skin. Theanimal 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 thedisease. As a general rule, unless infected cattle can be detecte d dur ing 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 excit- ed, it may die of anoxia (lack ofoxygen in the animal’s syste m). Second, antibiotic treat ments do little or nothing to affect the outcome of the disease when given dur ingthe late developmental or convalescent stage. Cattle that survive the clinical disease lose weight, abort calves, and recover slowly overa 2- or 3-month period. This is known as the
conv alesce nt stage, which lasts until normal blood values return . This stage is differe ntiated from the developmental stage by anincrease in the production of RBCs (eryt hropoiesis) in the periphera l blood, shown in an increase in hemoglobin levels and high totalwhite blood cell counts, among other character istics. Death loss es normally occur dur ing the late develop- mental stage or earlyconvalescent 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 bet ween anaplasmosis carriers and susceptible animals in the herd, and the amount of vector transmission. An increase in the ratio of carriers to susceptible animalsor 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 outbreak s, 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. Outbreak s occurring during the vector season.
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