FAZD Bovine Babesia Paper

1. FAZD Module: Bovine Babesiosis
Jose Santos Portugal and Pete D. Teel
Department of Entomology
Texas A&M University
College Station, Tx 77843-2475
History 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 cells
caused by intraerythrocytic protozoa transmitted by ticks. Progression of active infections
leads to depression, anemia, icterus, hemoglobinuria, neurological symptoms in some cases,
and death. The mortality rate can well exceed 50% in previously unexposed cattle of European
breeding (Bos taurus), while comparative mortalities in Bos indicus (Zebu/Brahman) and in Bos
taurus-Bos indicus crosses is generally less due to innate genetic resistance. Babesia bigemina
and B. bovis are the two principle agents causing bovine babesiosis throughout much of
tropical, sub-tropical and temperate climates of the world and these are the main focus of
concern for the United States.
In 1893, Theobald Smith and Frederic Kilborne demonstrated that certain ticks were
responsible for passing an agent (Babesia bigemina) from infected cattle to non-infected cattle
resulting in Texas cattle fever. This marked the first discovery of an arthropod vector of a
disease agent. The ticks involved were Boophilus annulatus and Boophilus microplus, recently
placed in the genus Rhipicephalus. The natural range of the two combined tick species in the
United States originally extended over 14 southern states and southern California.
In 1906, the USDA (United States Department of Agriculture formerly the United States
Bureau of Animal Industries) in conjunction with the TAHC (Texas Animal Health Commission
formerly the Livestock Sanitary Commission) initiated a regulatory and eradication program
aimed at the two tick species known to be the vector for the disease. The Tick Fever
Eradication Program was declared successful in 1943 making Bovine Babesiosis an “Exotic
Disease” and effectively purging the disease from the United States. However, both ticks and
the two Babesia pathogens remain endemic to neighboring Mexico. To prevent re-
establishment of ticks and disease, a permanent buffer zone was established along the
international boundary from Del Rio to below Brownsville, Texas. State-Federal tick
surveillance, 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 addition
to the substantial range of the tick vector and possible intermediate hosts continues to pose an
extreme threat to the American cattle and dairy industries. It is estimated that if the disease
reemerged in American herds, quarantine and eradication alone would present costs in the

2. billions per year. Historians will point out that this disease was the predominant factor in the
end 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 is
typically drier than R.microplus. Included in the endemic regions are Mexico and Central
America, the Middle East, the Mediterranean area, and regions of South America and Sothern
Asia. Occasionally, R.annulatus has been identified in quarantine zones on the Texas/Mexico
border, west of the Laredo area.
Rhipicephalus (Boophilus) microplus
This species of tick again utilizes cattle as its primary host. Like R.annulatus, this tick
prefers tropical and sub-tropical regions; however regions with higher rainfall are ideal. This
tick is found not only in Mexico, Central and South America and southern Asia, but is also
endemic to Australia, parts of Africa, the Indian subcontinent, and Southeast Asia. This tick is
also occasionally identified in quarantine zones on the Texas/Mexico and California/Mexico
borders.
Both ticks hatch from eggs dropped to the ground. The young ticks then seek out a host
to spend the remainder of their life on (typically cattle) by climbing vegetation. Both ticks have
only about 3-4 days to locate a host or they will die of starvation. Cooler temperatures can
extend this period before feeding.
When the ticks locate a host they begin to feed, achieving a higher growth stage after
each feeding. When sexual maturity is achieved, mating takes place. The female, laden with up
to 4,000 eggs each then drops from the host and deposits her eggs. The egg-laden female has a
range of up to 15 feet, which is the measurement used in double fencing methods. This
method ensures that a female dropped from an animal on one side of the fence cannot cover
the expanse and deposit eggs on the other side of the other fence. The complete life cycle
takes just short of a month.
Epidemiology and Transmission
Bovine Babesiosis is the name of the disease that is caused by two protozoans; Babesia
bigemina and Babesia bovis. The disease is spread when infected ticks take a blood meal from
cattle. As they feed, a small amount of regurgitated substances combined with saliva are
injected into the cattle. The protozoans are carried by the bloodstream and attempt to locate
suitable food and shelter. This is achieved by implanting themselves into the red blood cells of
the new host. As these immature parasites (trophozoites) grow, they gain the ability to
reproduce asexually. The “sister” copies of the parasite when done growing, lyse the walls of
the red blood cells and seek out new red blood cells to colonize.

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 the
tick after ingestion, where they are able to reproduce sexually for the first time. Both species
of parasites have been known to seek out the ovaries of a female tick and infect the eggs, thus
infecting future tick generations. Babesia can exist at such low levels in an animal that it may
be asymptomatic. This asymptomatic carrier can transmit the parasite to a large number of
ticks 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 identified
on various exotic Ungulates that are near impossible to monitor and treat. The specific species
that pose a potential problem to American cattle herds include White-tailed Deer and Nilgai
Antelope.
White-tailed Deer (Odocoileus virginianus)
White-tailed Deer are medium sized even toed Ungulates. Adult males in Texas have
been identified as having an annual home range of 1729-3733 acres. This extended range
allows for the potential to spread the Fever Tick among many cattle herds within a year. Cattle
and White-tailed deer are both herbivores and both graze the same areas. In south Texas, due
to few opportunities to avoid the mid-day sun, the deer and cattle have been known to both
frequent the same shade areas. In 1930, the population of White-tailed Deer was estimated to
be around 300,000, however due to very successful conservation efforts the population has
surged 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 exotic
hunting. Large groups of these animals have escaped captivity and formed feral herds. The
males are large, ranging from 240-630 lbs. 4-5 feet high at the shoulders and up to 6 ½ feet
long. The annual home range of this Ungulate has been observed up to 7.3 Km2. Physically
more closely related to cattle than antelopes, this species also inhabits areas frequented by
grazing 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 been
exposed 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 that
exposure does not necessarily equate to infection. Further research is currently underway. In
addition, Ivermectin treated corn has been introduced into areas with high deer populations in
an attempt to control the tick levels.

4. Detection and Diagnosis
Physical Symptoms
Very visible symptoms present when an animal is infected with Babesiosis. Due to the
nature of the protozoan in the blood stream, the lysing of the Red Blood Cells can result in
serious health concerns. The first is hemoglobinuria. Hemoglobinuria is the presence of
fragmented and ruptured Red Blood Cells in addition to free hemoglobin in the urine. This
condition causes the urine do be deep red in color and is readily identifiable, hence the
common name “Redwater”. When the blood cells are lysed in vivo, a severe anemic state
occurs. 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 response
in a health animal is mounted. This immune response leads quickly to a high fever that can
many times be worse than the anemia. Internal organ damage, especially in the spleen and
liver can initiate an Icteric state. This is due to the injured liver’s inability to pull unconjugated
bilirubin from the body. This bilirubin is a byproduct of hemoglobin catabolism. Neurological
signs may also present if the animal develops cerebral babesiosis. The symptoms associated
with this state include depression and lack of coordination.
Laboratory and Genetic Testing
The primary test performed by laboratory personnel is a microscopic observation of the
suspected infected animal’s blood. A Wright-Giemsa stain is performed and a slide is observed
under a microscope. If levels of the parasite are high enough (>1 parasite in 106 Red Blood
Cells) 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 to
be detected. Many slides may have to be made and observed to have an opportunity to see
the parasite. This fact makes the test unsuitable for general screening.
The use of PCR (Polymerase Chain Reaction) via ELISA (Enzyme Linked Immunosorbent
Assay) is used to detect the presence of antigens in the blood of cattle. This method is very
specific for each agent and is often used as a method of confirmation of exposure in many
countries. As the normal immunologic response in a mammal is to destroy an antigen and
present its constituents for the rest of the immune system to identify, the ability for PCR to
detect an exposed animal is relevant. However, the issue that persists with this method is that
exposure does not mean infection. Also, since this method is time consuming, requires
specially trained personnel in a laboratory setting and is expensive, it is unsuitable as a
screening method.
The IFA (Indirect Fluorescent Antibody) test has also showed the ability to detect the
presence of antibodies for Babesia. However, this test is not very specific for each of the two
agents and requires a fairly high antibody titer to present positive results. Also, this test again
does not diagnose infection; it simply detects exposure and antibody response.

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 on
eliminating the presence of the Rhipicephalus (Boophilus) intermediate vector ticks from the
U.S. This is accomplished by the utilization of multiple agents. The primary and most basic
method is the physical “scratching” of cattle for the ticks. This is performed by running ones
fingers across the skin of the cattle as well as intensive visual examination. The presence of a
fever tick may result in immediate quarantine and dipping of a herd. The dipping uses an
Acaracide 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 on
horseback to prevent the spread of the ticks via stray cattle; as well as to scratch and dip what
cattle they do find. The zone established for this intensive surveillance is known as the “buffer
zone”. The Buffer Zone stretches 500 miles from Brownsville to Del Rio, Texas and may be in
some parts between 200 yards and 6 miles wide. If a fever tick is found on cattle, an immediate
quarantine zone is established and the two week dip cycles commence for about a year to
prevent infestation. Ranchers that observe signs of infected cattle are asked to contact a local
veterinarian for further testing. If the disease is shown to be present, the TAHC along with
USDA APHIS begins an intensive investigation and quarantine procedure. The primary focus of
the 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 of
Bovine Babesia practice the policy of disease control. This method differs from the United
States 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 to
Babesia and have survived, often present immunity to later infections. In some instances it has
been noted that calves have been purposely introduced to the agent under controlled
conditions and utilizing supportive therapy to in turn induce immunity in adulthood. The use of
Imidocarb as a preventative of Babesiosis has been explored to induce immunity without
infection and has been approved for the treatment of infected cattle in Australia. However, the
use of Imidocarb has come under fire as it may be present at low levels in the beef and milk
produced 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 always
feasible. For instance, Mexico has introduced “La Campaña Nacional Contra La Garrapata
Boophilus spp.” (The National Campaign Against the Boophilus Tick) in the northern portion of

6. the country. It has seen limited success, although it faces obstacles such as lack of funding and
an uncontrollable socio-political climate. Australia has promoted a tick vaccine known as
tickGARD and Cuba has developed a tick vaccine known as GAVAC that have had impressive
results preventing Rhipicephalus (Boophilus) annulatus and mixed results with Rhipicephalus
(Boophilus) microplus. In a study performed by American researchers, the cattle vaccines killed
99.7% of female R. annulatus but less than 30% of female R. microplus.
Conclusion
The potential spread of Bovine Babesiosis among American cattle herds remains a
constant 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, a
program that has been successful for more than 100 years. On the other hand, many other
countries choose disease control and attempt to salvage infected cattle and reduce death rates
via supportive therapy and vaccinations. As the human population rises and larger cattle herds
are needed to feed world demand, the industry across the planet faces major obstacles. Recent
studies have suggested both tick species have developed limited immunities towards Acaracide
due to inconsistent use. In addition, as non-traditional tick hosts rise in number and occupy the
same geographic areas as cattle, the diseased will be harder to control.