Microbiology

Theileria Infections



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Tropical theileriosis and East Coast Fever are fatal diseases caused by infections of parasitic protozoa known as Theileria.  The diseases affect cattle, water buffalo, yak, and other ruminants in Africa, the Middle East, and Asia.  Introduced breeds of cattle that are more suseptable to the infection will have a much higher mortality rate than breeds that were bred locally.  Native ruminants may become infected but do not get sick and die from this disease due to the fact that they have evolved along with Theileria and have an already built up resistance to it.  Tropical theileriosis and East Coast Fever are caused by different species of Theileria (Theileria annulata and Theileria parva, respectively) and are found in different regions of the world although the life cycle of the parasite is similar in both diseases. 

Like other parasites, Theileria undergoes several stages of development.  Theileria is spread to its host through the saliva of ticks who introduce the organism into the bloodstream while feeding on the host animal.  The ticks are known as vectors, which is a term used to identify an organism that is responsible for the transmission of a disease but does not get infected itself by it.  The stage of the organism, once it has been introduced from the ticks, are known as sporozoites.  The sporozoites seek out the lymph nodes of the host and invade the lymph cells which are called lymphocytes.  The infected lymphocyte cells are then programmed by the organism to undergo a process called blast-transformation which makes the cells divide.  These newly produced cells carry new clones of the organism which are now known as schizonts.  These hijacked cells continue to divide and increase the number of schizonts exponentially.  After approximately 10-25 days, the schizonts develop into merozoits.  The merozoits then infect red blood cells where they then develop into piroplasms.  It is here at this stage that ticks pick up the organism from an infected animal while feeding on its blood. 

It is during the infection of the different stages of development that the animal host will show physical signs of infection of Theileria.  The most typical sign of infection is noticeably large lymph nodes and a fever.  As the infection progresses, the animal may develop anorexia, anemia, and will have increased mucous production from its mouth, nose and eyes.  Animals that are not treated with medication and do not have any immunity to Theileria will eventually die. 

Theileria infections can be prevented with vaccinations that also contain an antibiotic as well as a strain of the organism itself.  Prevention of animals being bitten by ticks is controlled by rotation of grazing pastures and with pesticides targeted at ticks.  Drugs such as buparvaquone and tetracycline can be used to treat infected animals but need to be administered as soon as the animal has become infected to be affective.

In nations where infections of Theileria are prevalent, livestock farmers must constantly monitor the herds for signs of infection.  Using a multiple step approach to control all faucets of the disease from spreading has been found to be the most effective way to keep it at bay.  Strict methods of screening must also be used when cattle are being moved from one area to another if they originated from an area where infections of Theileria are common. 

References:

http://www.cfsph.iastate.edu/Factsheets/pdfs/theileriosis_theileria_parva_and_theileria_annulata.pdf

http://www.theileria.org/index.htm

http://www.vet.uga.edu/vpp/clerk/siegel/index.php

http://www.ivis.org/advances/Disease_Factsheets/theileriosis_theileria_parva_and_theileria_annulata.pdf


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ARTICLE SOURCES AND CITATIONS
  • InfoBoxCallToAction ActionArrowhttp://www.cfsph.iastate.edu/Factsheets/pdfs/theileriosis_theileria_parva_and_theileria_annulata.pdf
  • InfoBoxCallToAction ActionArrowhttp://www.theileria.org/index.htm
  • InfoBoxCallToAction ActionArrowhttp://www.vet.uga.edu/vpp/clerk/siegel/index.php
  • InfoBoxCallToAction ActionArrowhttp://www.ivis.org/advances/Disease_Factsheets/theileriosis_theileria_parva_and_theileria_annulata.pdf