The Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) has a rich history. Over the 50 plus years we have existed, TVMDL professionals have worked tirelessly to provide the most accurate and up to date resources to our clients. The following excerpt is part of an ongoing series of articles written by TVMDL’s first director, Dr. William Sippel, and other professionals from the earlier days of TVMDL. Some articles were written for features in The Cattleman publication where others were case studies over recent diagnoses. We hope you enjoy this look back on TVMDL’s history.
Veterinary Outlook: Anaplasmosis
By William L. Sippel, V.M.D.
Anaplasmosis is one of the most prevalent infectious diseases of cattle in Texas. It is seasonal and is more frequent in the late summer and fall than at other times of the year. Anaplasmosis in caused by a red blood cell parasite that multiplies within the cells and destroys them, resembling malaria of people.
Anaplasmosis is spread by anything that transfers blood from a carrier animal to a susceptible animal. The most common vectors in Texas are large biting “horseflies.” Ticks are also important vectors in some areas. Other mechanical means of transferring blood, such as dehorners, nose tongs, needles, etc., may also spread this infection. Mosquitoes have been shown to be able to transmit the disease but the amount of blood they can transmit and their biting habits probably prevent them from being an important means of spread. The five to seven year cyclic nature of widespread outbreaks of anaplasmosis has been interrupted in recent years. Perhaps this is due to the adverse effects of weather, to reduction of biting fly populations by cattle egrets, vaccination programs and antibiotic feeding.
Experiments have shown that white-tailed-deer do not serve as a reservoir host for the disease in cattle. Young animals are more resistant than those over two years old.
Calves are seldom detected with the disease; whereas, in yearlings and upward, cases become more frequent. The disease is prevalent along the upper Gulf Coast and in the Sabine River Valley. It become less frequent further inland and occurs sporadically in the western half of the state. In areas where the disease in very prevalent, calves become infected when they are young and recover, usually without showing symptoms. They are then immune to the disease for life. If by chance they do not get exposed as calves, they remain susceptible and will probably come down with the disease later in life if in an endemic area. In parts of the state where the disease is less prevalent, a very high percentage of the cattle are susceptible. If a carrier animal is introduced, as often happens, a serious outbreak of the disease may occur if the vectors are present. Animals usually develop symptoms of the disease about 30 days after infection. New cases are usually not seen 30 days after the first hard freeze.
The disease causes anemia in affected cattle by destroying the red blood cells. The anaplasma agents invades the red blood cell, multiplies, and destroys it, releasing additional infective particles that invade other red blood cells and repeat the process. Apparently, young animals are able to regenerate blood and develop a resistance to the anaplasma organism with sufficient rapidity to overcome the infection. Older animals are evidently unable to accomplish this efficiently as calves.
Symptoms shown by affected cattle are generally related to the anemia produced by the red cell destruction and include fast breathing, lack of stamina, a fever, a propensity to try and hide and aggressiveness if discovered or approached by people. The urine of animals affected with anaplasmosis is a normal color, and usually their bowel movement is dry or firm unless they are disturbed and have several bowel movements. Signs observed at postmortem include pale mucous membranes and tissues, often tinted yellow. The spleen is swollen, the liver often mahogany colored and the gall bladder distended. The fecal material in the rectum is dry and the blood has a very thin “watery” appearance.
Anaplasmosis can easily be confused with leptospirosis or with Texas cattle fever. However, in these two diseases the urine is often colored red. Laboratory tests may be needed for differentiation and the diagnostic laboratories stand ready to assist you and your veterinarian in this effort.
The disease can be treated successfully in the early stages with the Tetracycline group of antibiotics. Blood transfusions and other supportive treatments are helpful. Great care must be taken in the treatment of affected animals not to cause over-exertion and death. With some animals it might be better not to attempt treatment, as to do so would certainly kill the animal.
Anything that can control the vectors, usually large biting flies, will prevent spread of the condition. Sanitary practices in the care and use of surgical instruments and needles are essential. Unfortunately, to date, a fly spray that is effective against horse flies (Tabanids) has not appeared on the market; however, rumors of such a product have been heard recently and will be a boon to cattlemen for more reasons than just anaplasmosis. Other methods of fly control, such as back rubber and dust bags, etc., are useful, but as cattlemen know, these are not highly effective against Tabanids.
Antibiotics in the feed can be provided under certain conditions to prevent spread of the disease. Anaplasmosis has been a problem among bulls introduced into an infected herd in the fall. Some owners maintain these animals on a preventative level of a Tetracycline drug in the feed to control the disease. Higher levels of antibiotics in the feed or intensive treatment intravenously for several days have been shown to be effective in eliminating the carrier state. Animals that have been treated and the carrier state eliminated again become susceptible. Drugs are in use elsewhere in the world that will cure the carrier state, but have not yet been approved for use in the United States. Regulations relative to drug resides must be borne in mind in the treatment or prevention of this disease.
Some ranchers, desiring to rid their herd of the disease, have tested their cattle and separated the carrier and clean animals. By separating these cattle by as little as 100 yards, transfer of the disease has been prevented. Apparently horse flies cannot fly this distance and get ready to bite again without blood on their mouth parts drying or disappearing and becoming noninfective.
Vaccines have been developed against anaplasmosis and one type has been used extensively in the United States. Use of the vaccine has been associated with the appearance of a fatal condition called yellow calf disease (neonatal isoerythrolysis). This condition has been a serious problem in some herds, whereas other herds have used the vaccine without any trouble. Your veterinarian should be consulted for his recommendations on the advisability of using the vaccine in your herd if anaplasmosis is a serious problem or serious threat.
The Institute of Tropical Veterinary Medicine at Texas A&M University has been working on anaplasmosis for several years. They are actively engaged in premunizing cattle against anaplasmosis and babesiosis (Texas cattle fever) so they will not die when shipped to Central and South America.