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Babesia bigemina |
Babesia is a piroplasmid protozoal parasite of blood cells and is found in the phylum Apicomplexa. This group is characterized by its round, rod or abstract shape and lack of any mobility structures such as cilia or flagella. The species B. bigemina was noted as the first vector-based disease described in history.1
There are many different Babesia species, several of which can infect humans. Babesia is a parasite, which means that it lives at the expense of its host.2 Babesiosis, the disease caused by infection with Babesia, is most common in New York (specifically, Long Island), Martha's Vineyard, and Nantucket, but fatalities are rare in humans.3
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Zoonotic Species of Babesia
Below are the different types of Babesia that may be infective to humans. They are found in many parts of the world and are normally transmitted to humans through ticks. The ticks are a biologic vector because part of the life cycle of the parasite takes place within the tick. B. bigemina affects cows and is one of the most common forms.2
| Species | Host | Vector | Distribution |
|---|---|---|---|
| B. divergens | Man | Ticks | Yugoslavia, Russia, Ireland, Scotland |
| B. bigemina | Man | Ticks | Subtropics and Tropics |
| B. equi | Man | Ticks | South America |
| B. microfti | Man | Ticks | North America (Eastern US, Wisconsin), Asia, Russia, India, Africa |
| B. duncani | Man | Ticks | North America (Western US) Asia |
Babesia bigemina
History
This disease is responsible for Texas cattle fever (also called red-water fever) and was to blame for severe losses in the cattle production industry in the 1880s. After this fiasco, much more time and research was put into studying this disease and in the late 1880s, Theobald Smith and F.L. Kilbourne discovered the cause. The tick "boophilus" was found to be a vector. This was the first description of a vector-based disease on record. This discovery then lead to the effective prevention method of controlling the tick population. This disease has been eradicated in the United States, but is endemic in Mexico and Central America. Farmers in this country are taking many precautions to prevent the disease from entering the United States again.2
Life Cycle
The infective stage of this parasite is termed the sporozoite and is found in the salivary gland of the tick. The sporozoite enters the vertebrate via tick bite.2
Vertebrate Host Cycle
Once the sporozoite enters the human (or any other vertebrate), it rapidly infects the red blood cells. In the red blood cells, these sporozoites mature to the trophozoite stage and then rapidly undergo the process of merogany (a type of multiple fission where the parasite reproduces asexually) to produce merozoites. These merozoites then burst out of the red blood cells and infect other red blood cells and continue to multiply. However, some merozoites stay in the red blood cells and wait for the next host. This next host is usually a tick that is infected when biting the animal.2
Biological Vector Host Cycle
Inside of a single tick, the merozoites contracted from the blood of the infected vertebrate transform into ray bodies, which fuse to form the zygote, which is called the primary kinete. However, in order for a vertebrate host to be infected, the parasite must infect the oocyte of the tick via transplacental transmission, which is accomplished when the primary kinetes leave the intestine of the tick and migrate to other cells, including those of the ovary. These primary kinetes then grow and multiply, producing cytomeres. These cytomeres then become new, differentiated kinetes. Some of the kinetes travel to the salivary gland and cause enlargement of the host cells. The kinetes then divide rapidly while the tick is feeding to produce a very large number of sporozoites. The infected tick may then bite a vertebrate animal (including a human), thus rendering them infected.2
Disease Pathogenesis of Babesia (Usually in Cows or Humans)
Clinical Signs
The temperature of the animal will rise rapidly, with a fever which persists for weeks. Dullness and listlessness with a loss of appetite are also common. Anemia due to loss of red blood cells becomes very severe. Also, because these red blood cells are being lysed (bursting), jaundice (a yellowing of the skin and eyes) and hemoglobinuria are common. Urine may appear red and internal organs may become damaged.2
Treatment
There are several types of drugs that may help to treat a babesia infection. The most common are clindamycin and atovaquone.1 However, these drugs may have extreme side effects and are not usually used in the United States. If they are used in food source animals, they may leave residues in the food that people ingest, which is a health concern.2
Prevention
In non-human animals, the best prevention is dipping to kill off and prevent infestation of ticks on the animal. This helps to ensure that the animals do not contract any parasites from the tick in the first place.2 Sentinels are animals that may give early warning of infection of a certain disease, which can, in turn, be used to prevent the spread of that disease in humans.4 Dogs, cows and rats are all important sentinels of babesia.5
References
- ^ a b Babesiosis. Center for Disease Control; Parasites and Health. Available at: http://www.dpd.cdc.gov/dpdx/HTML/Babesiosis.htm
- ^ a b c d e f g h i Roberts, L.S. and J. Janovy, Jr. Gerald D. Schmidt & Larry S. Roberts’ Foundations of Parasitology, 7th edition, Boston: McGraw-Hill, 2005. pp 166-170.
- ^ Cuhna, Burke A., M.D. Babesiosis. Available at: http://www.emedicine.com/med/topic195.htm
- ^ Sentinels of Health Threats from Recreational Waters. United States Geological Survey. Available at: http://health.usgs.gov/sentinels/recreational_waters.html
- ^ Quick, R.E., B.L. Herwald, J.W. Thomford, M.E. Garnett, M.L. Eberhard, M. Wilson, D.H. Spach, J.W. Dickerson, S.R.Telford 3rd, K.R. Steingart, R. Pollock, D.H. Persing, J.M. Kobayashi, D.D. Juranek, P.A. Conrad. Babesiosis in Washington State: a new species of Babesia? Available at: http://canarydatabase.org/record/560
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- This page was last modified on 6 November 2008, at 00:02.
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