Fazd Bovine Babesia Paper


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Fazd Bovine Babesia Paper

  1. 1. FAZD Module: Bovine Babesiosis Jose Santos Portugal and Pete D. Teel Department of Entomology Texas A&M University College Station, Tx 77843-2475History and General Information Bovine Babesiosis, also referred to as tick fever, Texas fever, Texas cattle fever,redwater, and piroplasmosis, is a disease of cattle resulting in the destruction of red blood cellscaused by intraerythrocytic protozoa transmitted by ticks. Progression of active infectionsleads to depression, anemia, icterus, hemoglobinuria, neurological symptoms in some cases,and death. The mortality rate can well exceed 50% in previously unexposed cattle of Europeanbreeding (Bos taurus), while comparative mortalities in Bos indicus (Zebu/Brahman) and in Bostaurus-Bos indicus crosses is generally less due to innate genetic resistance. Babesia bigeminaand B. bovis are the two principle agents causing bovine babesiosis throughout much oftropical, sub-tropical and temperate climates of the world and these are the main focus ofconcern for the United States.In 1893, Theobald Smith and Frederic Kilborne demonstrated that certain ticks wereresponsible for passing an agent (Babesia bigemina) from infected cattle to non-infected cattleresulting in Texas cattle fever. This marked the first discovery of an arthropod vector of adisease agent. The ticks involved were Boophilus annulatus and Boophilus microplus, recentlyplaced in the genus Rhipicephalus. The natural range of the two combined tick species in theUnited States originally extended over 14 southern states and southern California. In 1906, the USDA (United States Department of Agriculture formerly the United StatesBureau of Animal Industries) in conjunction with the TAHC (Texas Animal Health Commissionformerly the Livestock Sanitary Commission) initiated a regulatory and eradication programaimed at the two tick species known to be the vector for the disease. The Tick FeverEradication Program was declared successful in 1943 making Bovine Babesiosis an “ExoticDisease” and effectively purging the disease from the United States. However, both ticks andthe two Babesia pathogens remain endemic to neighboring Mexico. To prevent re-establishment of ticks and disease, a permanent buffer zone was established along theinternational boundary from Del Rio to below Brownsville, Texas. State-Federal ticksurveillance, detection and quarantine procedures have managed to prevent permanent re-establishment despite numerous incursions and outbreaks. The continued presence of Bovine Babesiosis in herds throughout the world in additionto the substantial range of the tick vector and possible intermediate hosts continues to pose anextreme threat to the American cattle and dairy industries. It is estimated that if the diseasereemerged in American herds, quarantine and eradication alone would present costs in the
  2. 2. billions per year. Historians will point out that this disease was the predominant factor in theend of the great American cattle drives in the late 19th and early 20th century.Tick Vector Overview Rhipicephalus (Boophilus) annulatus This species utilizes cattle as its primary host, however it will successfully feed on deer,horses, Buffalo and exotic Ungulates. The tick is adapted particularly to more tropical and sub-tropical regions, however, less than R.microplus. The climate that the tick can survive istypically drier than R.microplus. Included in the endemic regions are Mexico and CentralAmerica, the Middle East, the Mediterranean area, and regions of South America and SothernAsia. Occasionally, R.annulatus has been identified in quarantine zones on the Texas/Mexicoborder, west of the Laredo area. Rhipicephalus (Boophilus) microplus This species of tick again utilizes cattle as its primary host. Like R.annulatus, this tickprefers tropical and sub-tropical regions; however regions with higher rainfall are ideal. Thistick is found not only in Mexico, Central and South America and southern Asia, but is alsoendemic to Australia, parts of Africa, the Indian subcontinent, and Southeast Asia. This tick isalso occasionally identified in quarantine zones on the Texas/Mexico and California/Mexicoborders. Both ticks hatch from eggs dropped to the ground. The young ticks then seek out a hostto spend the remainder of their life on (typically cattle) by climbing vegetation. Both ticks haveonly about 3-4 days to locate a host or they will die of starvation. Cooler temperatures canextend this period before feeding. When the ticks locate a host they begin to feed, achieving a higher growth stage aftereach feeding. When sexual maturity is achieved, mating takes place. The female, laden with upto 4,000 eggs each then drops from the host and deposits her eggs. The egg-laden female has arange of up to 15 feet, which is the measurement used in double fencing methods. Thismethod ensures that a female dropped from an animal on one side of the fence cannot coverthe expanse and deposit eggs on the other side of the other fence. The complete life cycletakes just short of a month.Epidemiology and Transmission Bovine Babesiosis is the name of the disease that is caused by two protozoans; Babesiabigemina and Babesia bovis. The disease is spread when infected ticks take a blood meal fromcattle. As they feed, a small amount of regurgitated substances combined with saliva areinjected into the cattle. The protozoans are carried by the bloodstream and attempt to locatesuitable food and shelter. This is achieved by implanting themselves into the red blood cells ofthe new host. As these immature parasites (trophozoites) grow, they gain the ability toreproduce asexually. The “sister” copies of the parasite when done growing, lyse the walls ofthe red blood cells and seek out new red blood cells to colonize.
  3. 3. The disease is spread to the intermediate tick host when an uninfected Rhipicephalus(Boophilus) tick takes a blood meal from an infected host. The parasite moves to the gut of thetick after ingestion, where they are able to reproduce sexually for the first time. Both speciesof parasites have been known to seek out the ovaries of a female tick and infect the eggs, thusinfecting future tick generations. Babesia can exist at such low levels in an animal that it maybe asymptomatic. This asymptomatic carrier can transmit the parasite to a large number ofticks and maintain the presence of or increase the level of the parasite in a herd.Extended Risk-Native and Exotic Ungulates Although the main host of Bovine Babesiosis is cattle, the tick itself has been identifiedon various exotic Ungulates that are near impossible to monitor and treat. The specific speciesthat pose a potential problem to American cattle herds include White-tailed Deer and NilgaiAntelope. White-tailed Deer (Odocoileus virginianus) White-tailed Deer are medium sized even toed Ungulates. Adult males in Texas havebeen identified as having an annual home range of 1729-3733 acres. This extended rangeallows for the potential to spread the Fever Tick among many cattle herds within a year. Cattleand White-tailed deer are both herbivores and both graze the same areas. In south Texas, dueto few opportunities to avoid the mid-day sun, the deer and cattle have been known to bothfrequent the same shade areas. In 1930, the population of White-tailed Deer was estimated tobe around 300,000, however due to very successful conservation efforts the population hassurged to the point where they have become agricultural pests. Nilgai Antelope “Blue Bull” (Boselaphus tragocamelus) Nilgai antelope are an exotic species with origins in parts of India, Pakistan and Nepal.The antelope were introduced to portions of South Texas and Alabama for big game exotichunting. Large groups of these animals have escaped captivity and formed feral herds. Themales are large, ranging from 240-630 lbs. 4-5 feet high at the shoulders and up to 6 ½ feetlong. The annual home range of this Ungulate has been observed up to 7.3 Km2. Physicallymore closely related to cattle than antelopes, this species also inhabits areas frequented bygrazing cattle. Other Ungulate species that have been identified as Fever Tick carriers include Horses,Buffalo, donkeys and occasionally sheep. Genetic testing by PCR and Elisa has shown that Nilgai in Mexico and in India have beenexposed to both Babesia spp. In addition, genetic testing by PCR has shown exposed White-tailed Deer in Mexico and Texas. The testing is inconclusive in this matter due to the fact thatexposure does not necessarily equate to infection. Further research is currently underway. Inaddition, Ivermectin treated corn has been introduced into areas with high deer populations inan attempt to control the tick levels.
  4. 4. Detection and Diagnosis Physical Symptoms Very visible symptoms present when an animal is infected with Babesiosis. Due to thenature of the protozoan in the blood stream, the lysing of the Red Blood Cells can result inserious health concerns. The first is hemoglobinuria. Hemoglobinuria is the presence offragmented and ruptured Red Blood Cells in addition to free hemoglobin in the urine. Thiscondition causes the urine do be deep red in color and is readily identifiable, hence thecommon name “Redwater”. When the blood cells are lysed in vivo, a severe anemic stateoccurs. This leads to lethargy, weight loss and an increased pallor in the mucous membranes.Eventually if left untreated or if the animal cannot combat it through its own immune system,anemia leads to death. As the protozoan is identified as a foreign antigen, an immune responsein a health animal is mounted. This immune response leads quickly to a high fever that canmany times be worse than the anemia. Internal organ damage, especially in the spleen andliver can initiate an Icteric state. This is due to the injured liver’s inability to pull unconjugatedbilirubin from the body. This bilirubin is a byproduct of hemoglobin catabolism. Neurologicalsigns may also present if the animal develops cerebral babesiosis. The symptoms associatedwith this state include depression and lack of coordination. Laboratory and Genetic Testing The primary test performed by laboratory personnel is a microscopic observation of thesuspected infected animal’s blood. A Wright-Giemsa stain is performed and a slide is observedunder a microscope. If levels of the parasite are high enough (>1 parasite in 106 Red BloodCells) the trophozoites can be observed in the cells along with sporozoites and gametocytes.The limitation to the test is that parasite levels in the blood have to be at a high enough level tobe detected. Many slides may have to be made and observed to have an opportunity to seethe parasite. This fact makes the test unsuitable for general screening. The use of PCR (Polymerase Chain Reaction) via ELISA (Enzyme Linked ImmunosorbentAssay) is used to detect the presence of antigens in the blood of cattle. This method is veryspecific for each agent and is often used as a method of confirmation of exposure in manycountries. As the normal immunologic response in a mammal is to destroy an antigen andpresent its constituents for the rest of the immune system to identify, the ability for PCR todetect an exposed animal is relevant. However, the issue that persists with this method is thatexposure does not mean infection. Also, since this method is time consuming, requiresspecially trained personnel in a laboratory setting and is expensive, it is unsuitable as ascreening method. The IFA (Indirect Fluorescent Antibody) test has also showed the ability to detect thepresence of antibodies for Babesia. However, this test is not very specific for each of the twoagents and requires a fairly high antibody titer to present positive results. Also, this test againdoes not diagnose infection; it simply detects exposure and antibody response.
  5. 5. Further research has explored the use of in-vitro cultures and latex agglutination,however neither method has been adapted on a regular bases.Eradication, Prevention and Control (US and Worldwide) United States In the United States, a tick eradication policy is practiced. This policy focuses oneliminating the presence of the Rhipicephalus (Boophilus) intermediate vector ticks from theU.S. This is accomplished by the utilization of multiple agents. The primary and most basicmethod is the physical “scratching” of cattle for the ticks. This is performed by running onesfingers across the skin of the cattle as well as intensive visual examination. The presence of afever tick may result in immediate quarantine and dipping of a herd. The dipping uses anAcaracide solution on a 14 day cycle to kill the ectoparasites present on the cattle. The USDA,along with the TAHC, employ a team of “Tick Riders” that monitor the Texas/Mexico border onhorseback to prevent the spread of the ticks via stray cattle; as well as to scratch and dip whatcattle they do find. The zone established for this intensive surveillance is known as the “bufferzone”. The Buffer Zone stretches 500 miles from Brownsville to Del Rio, Texas and may be insome parts between 200 yards and 6 miles wide. If a fever tick is found on cattle, an immediatequarantine zone is established and the two week dip cycles commence for about a year toprevent infestation. Ranchers that observe signs of infected cattle are asked to contact a localveterinarian for further testing. If the disease is shown to be present, the TAHC along withUSDA APHIS begins an intensive investigation and quarantine procedure. The primary focus ofthe United States concerning Bovine Babesia is the eradication of the Fever Tick. Mexico, Brazil, Australia and the Majority Countries at Risk Mexico, along with Brazil, Australia and most other countries that face the scourge ofBovine Babesia practice the policy of disease control. This method differs from the UnitedStates in that they U.S. practices eradication of the Fever Tick, where as in disease control,immunization and supportive therapy are applied to cattle. Cattle that have been exposed toBabesia and have survived, often present immunity to later infections. In some instances it hasbeen noted that calves have been purposely introduced to the agent under controlledconditions and utilizing supportive therapy to in turn induce immunity in adulthood. The use ofImidocarb as a preventative of Babesiosis has been explored to induce immunity withoutinfection and has been approved for the treatment of infected cattle in Australia. However, theuse of Imidocarb has come under fire as it may be present at low levels in the beef and milkproduced by the cattle. It is incorrect to say that these countries do not participate in tick eradication programs,just that due to the situation financially or geographically many times eradication is not alwaysfeasible. For instance, Mexico has introduced “La Campaña Nacional Contra La GarrapataBoophilus spp.” (The National Campaign Against the Boophilus Tick) in the northern portion of
  6. 6. the country. It has seen limited success, although it faces obstacles such as lack of funding andan uncontrollable socio-political climate. Australia has promoted a tick vaccine known astickGARD and Cuba has developed a tick vaccine known as GAVAC that have had impressiveresults preventing Rhipicephalus (Boophilus) annulatus and mixed results with Rhipicephalus(Boophilus) microplus. In a study performed by American researchers, the cattle vaccines killed99.7% of female R. annulatus but less than 30% of female R. microplus.Conclusion The potential spread of Bovine Babesiosis among American cattle herds remains aconstant threat. The losses due to the naïve state of American herds would be staggering.American policy dictates eradication of the vector Fever Tick to halt the spread of Babesia, aprogram that has been successful for more than 100 years. On the other hand, many othercountries choose disease control and attempt to salvage infected cattle and reduce death ratesvia supportive therapy and vaccinations. As the human population rises and larger cattle herdsare needed to feed world demand, the industry across the planet faces major obstacles. Recentstudies have suggested both tick species have developed limited immunities towards Acaracidedue to inconsistent use. In addition, as non-traditional tick hosts rise in number and occupy thesame geographic areas as cattle, the diseased will be harder to control.