Babesia

Genus of protozoan parasites

Automatic taxobox
| image = Blood smear of Babesia microti, annotated. png
| image alt = Blood smear of Babesia microti
| image caption = Blood smear of Babesia microti
| taxon = Babesia
| authority = Starcovici, 1893
| synonyms =
| synonyms ref =
| subdivision ranks = Species
| subdivision =
Babesia annae
Babesia ardeae
Babesia behnkei
Babesia bennetti
Babesia bicornis
Babesia bigemina
Babesia bovis
Babesia caballi
Babesia canis
Babesia canis canis
Babesia canis rossi
Babesia canis vogeli
Babesia capreoli
Babesia crassa
Babesia divergens
Babesia gibsoni
Babesia hongkongensis
Babesia kiwiensis
Babesia lohae
Babesia mackerrasorum
Babesia major
Babesia motasi
Babesia muratovi
Babesia occultans
Babesia odocoilei
Babesia orientalis
Babesia ovata
Babesia ovis
Babesia pecorum
Babesia peircei
Babesia poelea
Babesia ugwidiensis
Babesia uriae
Babesia venatorum
Babesia vesperuginis
Babesia vitalii

B. microti ("Archaeopiroplasmida") group: also called Nuttallia, is an apicomplexan parasite that infects red blood cells and is transmitted by ticks. Originally discovered by the Romanian bacteriologist Victor Babeș in 1888, over 100 species of Babesia have since been identified. Babesia species infect livestock worldwide, wild and domestic vertebrate animals, and occasionally humans, where they cause the disease babesiosis. In the United States, B. microti is the most common strain of the few which have been documented to cause disease in humans.

Babesia is a protozoan parasite found to infect vertebrate animals, mostly livestock mammals and birds, but also occasionally humans. Common names of the disease that Babesia microti causes are Texas cattle fever, redwater fever, tick fever, and Nantucket fever. Another "western" group is also separate from core Babesia.

For centuries, the animal disease was known to be a serious illness for wild and domesticated animals, especially cattle. In 1888, Victor Babeș first identified the causative agent in Romania and believed it to be due to the bacterium he named Haematococcus bovis. He documented the disease by describing signs of a severe hemolytic illness seen uniquely in cattle and sheep. In 1893, Americans Theobald Smith and Fred Kilborne identified the parasite as the cause of Texas cattle fever, the same disease described by Babeș. They also identified the tick as the transmitting agent, a discovery which first introduced the concept of arthropods functioning as disease vectors. It was believed to be a disease that only affected nonhuman mammals, but in 1957, the first case of babesiosis was seen in a human.

Babesia show host specificity, allowing many different subspecies of Babesia to emerge, each infecting a different kind of vertebrate organism. While B. bovis and Babesia bigemina prefer to infect cattle in tropical environments, they can infect other animals, such as the white tailed deer. Partial RNA sequencing of canine piroplasms has identified a number of additional species.

The life cycle of B. microti, which is typical of parasites in the genus, requires a biological stage in a rodent or deer host. It is transmitted by ticks of the family Ixodidae between these hosts. To begin, the tick as the definitive host becomes infected itself, as it takes up gametocytes when attached for a blood meal. It also introduces the Babesia into the intermediate host (e. g. cattle) when taking a blood meal. As Babesia enter the animal's red blood cells (erythrocytes), they are called sporozoites. Within the red blood cell, the protozoa become cyclical and develop into a trophozoite ring. The trophozoites moult into merozoites, which have a tetrad structure coined a Maltese cross form. Trophozoite and merozoite growth ruptures the host erythrocyte, leading to the release of vermicules, the infectious parasitic bodies, which rapidly spread the protozoa throughout the blood. The emergence of tick borne diseases has been found to coincide with climate change. The correlation between climate change and the incidence of tick borne diseases is not known to be strong enough to count as a major factor. This may explain why B. bigemina infection in cattle in the hilly region of Meghalaya has increased. These woodland species are hypothesized reservoirs because although they are known to harbor the disease, complete reservoir competence has not yet been shown. Most cases of transmission between humans are attributed to a tick vector. As of 2003, the Centers for Disease Control and Prevention (CDC) acknowledged more than 40 cases of babesiosis contracted from transfusions of packed red blood cells (PRBC), as well as two infections documented from organ transplantation. PRBC transfusions that cause infections were identified through testing the blood donor for B. microti antibodies. The occurrence of Babesia transmission through PRBC blood transfusions puts pressure on governmental organizations (such as the CDC) to heighten standard measures for screening blood donations. Transmission is also possible through congenital transmission (from an infected mother to her baby). As symptoms may not appear, many women may not be aware they are infected during pregnancy, and therefore a measurement of congenital transmission rate is not known at this time. Currently, no vectors for avian Babesia have been identified, but they are assumed to be ticks.

Of the species to infect humans, B. microti is most common in the Americas, whereas B. divergens is the predominant strain found in Europe. Endemic areas are regions of tick habitat, including the forest regions of the northeastern United States and temperate regions of Europe. B. poelea was reported from a masked booby (Sula dactylatra melanops) from Desnoeufs Island, Amirantes, Seychelles. Babesia peircei has been observed in 2 species of penguins, the jackass penguin (Sphenicus demersus) from South Africa and the little penguin (Eduyptula minor) from southern Australia. Babesia bennetti was associated from the yellow legged gull (Larus cachinnans) from Benidorm Island off the coast of Spain.

Bovine babesiosis caused by B. bovis is an important constraint for cattle industries worldwide.

Signs of infection with B. microti usually arise one to eight weeks after a bite from an infectious tick. Individuals with normal immune function and healthy spleens often recover without treatment. They have severe hemolytic anemia, and occasional hepatomegaly has been documented. Parasitemia levels can reach up to 85% in patients without spleens, compared to 1–10% in individuals with spleens and effective immune systems.

As a protozoan parasite, the most effective way to identify Babesia infection is through blood sample testing.

Babesia species enter red blood cells (erythrocytes) at the sporozoite stage. Within the red blood cell, the protozoa become cyclical and develop into a trophozoite ring. The trophozoites moult into merozoites, which have a tetrad structure coined a Maltese cross form. In severe cases, blood exchange transfusions have been performed to lower the parasitic load in an individual. Treatment for babesiosis consisted of primaquine (1 mg/kg PO q24h for 10 days; primaquine phosphate 1.76%m/v in stabilized solution, Primaquin Solution, MedPet Ltd, Benrose, South Africa). After, treatment was followed by a phospholipid supplement (1 capsule/bird PO q24h for 12 days; deoiled, enriched phospholipids from soybeans, 300 mg/capsule, Essentiale Extreme, Sanofi Aventis Ltd, Midrand, South Africa); as an attempt to mitigate potential hepatotoxic effects of primaquine. To prevent transmission of Babesia and other tickborne pathogens, all birds with visible ectoparasites are treated with pesticide powder (carbaryl 50 g/kg) upon admission, and the facilities are thoroughly cleaned on a daily basis.

In 1906, efforts were made to eradicate the tick vector of bovine babesiosis in the United States. This eradication was recorded as being successfully completed four decades later. Effective control can be achieved by vaccination with live attenuated phenotypes of the parasite. The vaccines have a number of drawbacks, so better, safer vaccines are still being researched. In recent years, a number of parasite proteins with immunogenic potential have been discovered. Through polymerase chain reaction, genetic sequencing, and bioinformatics analysis of the genes, a high degree of conservation (98–100%) was found among Brazilian isolates of B. bovis and the T2Bo isolate. Thus, these genes are considered for inclusion in a recombinant cocktail vaccine for cattle babesiosis caused by B. bovis.

The most effective public health measure for Babesia is to avoid tick exposure. This can be through personal prevention such as avoiding tick infested areas (especially during high tick season between May and September), remaining covered with light clothing, searching for ticks after being outdoors, and removing discovered ticks from the skin. Other measures include applying DEET, a common repellent that is effective against ticks and insects. (For people who react adversely to DEET, alternative insect repellents should be used.) On a state level, if health departments are particularly motivated, tick elimination is a possibility. In 1906, efforts were made to eradicate the tick vector of the bovine disease form of babesiosis in the United States. This eradication was recorded as being successfully completed four decades later. Complete eradication through vector control would be a long term project, which would significantly reduce the prevalence of both babesiosis and Lyme disease, but, as public health departments are often short on funding, preventive measures are more recommended. Due to the relatively low prevalence of the human disease and the presence of several reservoirs, babesiosis has not been a candidate for vaccines. In regions where ticks of domestic animals are routinely controlled with chemical acaricides to reduce incidence of infection with B. bovis and B. bigemina, the risk to humans from these parasites will be reduced.