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Babesiosis or piroplasmosis is a malaria-like parasitic disease caused by infection with a eukaryotic parasite in the order Piroplasmida, typically a Babesia or Theileria, in the phylum Apicomplexa. Human babesiosis transmission via tick bite is most common in the Northeastern and Midwestern United States and parts of Europe, and sporadic throughout the rest of the world. It occurs in warm weather. People can get infected with Babesia parasites by the bite of an infected tick, by getting a blood transfusion from an infected donor of blood products, or by congenital transmission (an infected mother to her baby). Ticks transmit the human strain of babesiosis, so it often presents with other tick-borne illnesses such as Lyme disease. After Trypanosoma, Babesia is thought to be the second-most common blood parasite of mammals. They can have major adverse effects on the health of domestic animals in areas without severe winters. In cattle, the disease is known as Texas cattle fever or redwater.
Less common symptoms and physical exam findings of mild-to-moderate babesiosis:
In more severe cases, symptoms similar to malaria occur, with fevers up to 40.5 °C (105 °F), shaking chills, and severe anemia (hemolytic anemia). Organ failure may follow, including adult respiratory distress syndrome. Sepsis in people who have had a splenectomy can occur rapidly, consistent with overwhelming post-splenectomy infection. Severe cases are also more likely to occur in the very young, very old, and persons with immunodeficiency, such as HIV/AIDS patients.
A reported increase in human babesiosis diagnoses in the 2000s is thought to be caused by more widespread testing and higher numbers of people with immunodeficiencies coming in contact with ticks, the disease vector. Little is known about the occurrence of Babesia species in malaria-endemic areas, where Babesia can easily be misdiagnosed as Plasmodium. Human patients with repeat babesiosis infection may exhibit premunity.
Unlike the Plasmodium parasites that cause malaria, Babesia species rarely exhibit an exoerythrocytic phase with trophozoite forms.
In nonhuman animals, Babesia canis rossi, Babesia bigemina, and Babesia bovis cause particularly severe forms of the disease, including severe haemolytic anaemia, with positive erythrocyte-in-saline-agglutination test indicating an immune-mediated component to the haemolysis. Common sequelae include haemoglobinuria "red-water", disseminated intravascular coagulation, and "cerebral babesiosis" caused by sludging of erythrocytes in cerebral capillaries.
In bovine species, the organism causes hemolytic anemia, so an infected animal shows pale mucous membranes initially. As the levels of bilirubin (a byproduct of red blood cell lysis) continue to increase, the visible mucous membranes become yellow (icterus) due to the failure of the liver to metabolize the excess bilirubin. Hemoglobinuria is seen due to the excretion of red-blood-cell lysis byproducts via the kidneys. A fever of 40.5 °C (105 °F) develops due to the release of inflammatory byproducts.
So-called "Maltese cross formations" on the blood film are diagnostic (pathognomonic) of babesiosis since they are not seen in malaria, the primary differential diagnosis. Careful examination of multiple smear test may be necessary, since Babesia may infect less than 1% of circulating red blood cells, thus be easily overlooked.
Serology for antibody against Babesia (both Immunoglobulin G and IgM) can detect low-level infection in cases with high clinical suspicion, but negative blood film examinations. Serology is also useful for differentiating babesiosis from malaria in cases where people are at risk for both infections. Since detectable antibody responses require about a week after infection to develop, serologic testing may be falsely negative early in the disease course.
A polymerase chain reaction (PCR) test has been developed for the detection of Babesia from the peripheral blood. PCR may be at least as sensitive and specific as blood-film examination in diagnosing babesiosis, though it is also significantly more expensive. Most often, PCR testing is used in conjunction with blood film examination and possibly serology.
Other laboratory findings include decreased numbers of red blood cells and platelets on complete blood count.
In animals, babesiosis is suspected by observation of clinical signs (hemoglobinuria and anemia) in animals in endemic areas. Diagnosis is confirmed by observation of merozoites on a thin film blood smear examined at maximum magnification under oil using Romonovski stains (methylene blue and eosin). This is a routine part of the veterinary examination of dogs and ruminants in regions where babesiosis is endemic.
Babesia canis and B. bigemina are "large Babesia species" that form paired merozoites in the erythrocytes, commonly described as resembling "two pears hanging together", rather than the "Maltese cross" of the "small Babesia species". Their merozoites are around twice the size of small ones.
Cerebral babesiosis is suspected in vivo when neurological signs (often severe) are seen in cattle that are positive for B. bovis on blood smear, but this has yet to be proven scientifically. Outspoken red discoloration of the grey matter post-mortem further strengthens suspicion of cerebral babesiosis. Diagnosis is confirmed post-mortem by observation of Babesia-infected erythrocytes sludged in the cerebral cortical capillaries in a brain smear.
Imidocarb is a drug used for the treatment of babesiosis in dogs. Extracts of the poisonous, bulbous plant Boophone disticha are used in the folk medicine of South Africa to treat equine babesiosis. B. disticha is a member of the daffodil family Amaryllidaceae and has also been used in preparations employed as arrow poisons, hallucinogens, and in embalming. The plant is rich in alkaloids, some of which display an action similar to that of scopolamine.
In the United States, the majority of babesiosis cases are caused by B. microti, and occur in the Northeast and northern Midwest from May through October. Areas with especially high rates include eastern Long Island, Fire Island, Nantucket Island, and Martha's Vineyard. The Centers for Disease Control and Prevention now requires state health departments to report infections using Form OMB No. 0920-0728. In 2014, Rhode Island had an incidence of 16.3 reported infections per 100,000 people.
In Europe, B. divergens is the primary cause of infectious babesiosis and is transmitted by I. ricinus.
Babesiosis has emerged in the Lower Hudson Valley, New York, since 2001.
Related news articles:
In Australia, one locally-acquired case of B. microti has been reported, which was fatal. A subsequent investigation found no additional evidence of human Babesiosis in over 7000 patient samples, leading the authors to conclude that Babesiosis was rare in Australia. A similar disease in cattle, commonly known as tick fever, is spread by Babesia bovis and Babesia bigemina in the introduced cattle tick Rhipicephalus microplus. This disease is found in eastern and northern Australia.
| B. duncani |
| B. divergens |
| B. venatorum |
| B. microti |
| Uncharacterized spp. |
| B. microti |
| Babesia KO1 |
| B. microti |
| Uncharacterized spp. |
In 1957, the first human case was documented in a splenectomy Croatian herdsman. The agent was B. divergens. In 1969, the first case was reported in an immunocompetent individual on Nantucket Island. The agent was B. microti, and the vector was the tick I. scapularis. Horse babesiosis (caused by the protozoan Theileria equi) is also known as piroplasmosis (from the Latin language piro, meaning pear + Greek language plasma, a thing formed).
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