Vet Column 6-1-09 |

Vet Column 6-1-09

David L. Morris, DVM, Ph.D.
Fort Collins, Colo.

Eradicated from the United States in 1943, Texas Cattle Fever, also known as Texas Fever, Redwater, Tick Fever, and Piroplasmosis, was once well established from Texas to Florida along all the Gulf Coast states, as well as southern California. Its impact on the cattle industry led to the formation of the Texas Animal Health Commission in 1893 and the United States Animal Health Association in 1897 to develop collective approaches for managing the disease, disseminate accurate information, and promote research regarding the disease.

Caused by protozoa of the Babesia genus, the disease primarily affects the red blood cells, causing anemia and destruction of red blood cells. Cattle go off feed and develop a high fever. Most cases of babesiosis, the more accurate name for Texas Cattle Fever, are seen in adult cattle. Cattle younger than nine months-of-age usually do not develop clinical signs. Because the red blood cells are destroyed in the bloodstream, the released hemoglobin passes through the kidneys and colors the urine red; hence, the name Redwater. If the cattle survive, the anemic crisis generally passes within a week.

In the evolution of mammalian animal disease understanding, Texas Cattle Fever was a milestone in determining that arthropods can be vectors in the transmission of disease. Bovine babesiosis can be found wherever tick vectors exist. The primary tick vectors are Rhipicephalus microplus (formerly Boophilus microplus) (Southern Cattle Tick) and Rhipicephalus annulatus (formerly Boophilus annulatus) (North American Texas Fever Tick). These two ticks transmit the causative protozoa of Babesia bovis and Babesia bigemina although other protozoa and associated specific tick species do exist such as Ixodes ricinus (common tick, wood tick, deer tick, sheep tick, castor bean tick, pasture tick, face tick are common names).

Babesiosis in cattle is most common in tropical and subtropical areas. The disease is particularly important in Asia, Africa, Central and South America, parts of southern Europe, and Australia. Once endemic to the southern United States, the disease has been more recently restricted to a buffer quarantine zone along the Mexican border. Over the past few years, however, the presence of the specific ticks, and their associated importance to the development of the disease, have been detected in greater numbers and in larger geographic areas in this border area. The specific ticks have also been detected in wildlife.

Ticks become infected with Babesiosis when they ingest parasites in the blood of infected cattle. Inside the tick, Babesia zygotes multiply, invading many of the tick body organs, including the ovaries. Babesia species are readily passed to the next generation of ticks in the eggs produced. Some species of Babesia can survive in tick populations for at least four years even if cattle are not present. When an infected tick attaches to a new host, Babesia are stimulated to undergo their final maturation. Babesia, depending upon the specific species, become infective in two to nine days after the ticks attach.

Following tick infestation, the clinical signs of babesiosis in cattle appear in two to three weeks. Babesia are maintained in cattle populations by asymptomatic carriers that have recovered from acute disease. Although a vaccine is available, it is a live vaccine and its use presents safety concerns. As a result, the primary means to control and/or eradicate the disease is associated with controlling ticks.

To eradicate the disease in the United States, cattle were treated for ticks every two to three weeks. With the potential for tick resistance to available acaricides for treatment, the ability to control the disease is a concern. Due to the expanding surveillance area in south Texas currently, and the ability to transport cattle over long distances in a short period of time, this is a cattle disease that should be of concern to all beef and dairy producers.

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