Babesiosis

Babesiosis
Specialty	Infectious diseases

Babesiosis is an uncommon malaria-like parasitic disease caused by piroplasms, protozoan parasites of the genus Babesia.

Terminology

The disease is named for the genus of the causative organism, which was in turn named after the bacteriologist Victor Babeş. The disease was not known to significantly affect humans until the work of Andrew Spielman in the late twentieth century. Equine babesiosis is also known as piroplasmosis.

Epidemiology

Babesiosis is a vector-borne illness usually transmitted by ticks. (Babesia microti uses the same tick vector, Ixodes scapularis, as Lyme disease does, and frequently occurs in conjunction with it.) In babesia-endemic areas, the organism can also be transmitted by blood transfusion. In North America, the disease exists mostly in Eastern Long-Island and its barrier island, Fire Island, and the islands off the coast of Massachusetts. It is sometimes called "The Malaria of The North East."

Babesiosis causes a disease very similar to Malaria. In mild cases, people may experience mild fevers and anemia. In more severe cases, fevers go up to 105°F / 40°C with shaking chills, and anemia (hemolytic anemia) can become severe. Organ failure may follow including adult respiratory distress syndrome.

Infection with Babesia parasites can be asymptomatic or cause a mild non-specific illness, and therefore many cases go unnoticed. It may also cause severe disease. While most severe cases occur in the very young, very old, or persons with underlying medical conditions (such as immunodeficiency) and those without a spleen, they can occur in normal individuals. Indeed, both the incidence or all cases of babesiosis and severe cases are increasing rapidly. Some cases are identified when patients with another tick-borne illness are screened for babesiosis.

Little is known about the occurrence of Babesia species in malaria-endemic areas, where Babesia can easily be misdiagnosed as Plasmodium.

Pathophysiology

Babesia life cycle

Babesia parasites reproduce in red blood cells, where they can be seen as cross-shaped inclusions (4 merozoites asexually budding but attached together forming a structure looking like a "Maltese Cross") and cause hemolytic anemia, quite similar to malaria.

Note that unlike the Plasmodium parasites that cause malaria, Babesia species lack an exo-erythrocytic phase, so the liver is usually not affected.

In animals Babesia canis rossi, Babesia bigemina, and Babesia bovis cause particularly severe forms of the disease that include a 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 coaguation (DIC) and "cerebral babesiosis" caused by sludging of erythrocytes in cerebral capilaries.

Diagnosis

Babesiosis is easy to diagnose but only if it is suspected. It will not show up on any routine tests. It must be suspected when a persons with exposure in an endemic area develops persistent fevers and hemolytic anemia. Babesiosis can be diagnosed by direct examination of the blood (see photo), with serology, or with PCR-based tests. The so-called Maltese cross formations are essentially pathognomonic of babesiosis, since they are not seen in malaria, the primary consideration in the differential diagnosis. 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 (haemoglobinuria and anaemia) in animals in endemic areas. Diagnosis is confirmed by observation of merozoites on 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 Babesia bigemina are "large babesias" that form paired merozoites in the erythrocytes , commonly described as resembling "two pears hanging together", rather than the "Maltese Cross" of the "small babesias". Their merozoites are approximately twice the size of small babesias.

Cerebral babesiosis is suspected in-vivo when neurological signs (often severe) are seen in cattle that are positive for babesia bovis on blood smear. Outspoken red discolouration of the grey matter on post-mortem further strengthens suspicion of cerebral babesiosis. Diagnosis is confirmed post-mortem by observation of babesia infected erythrocytes sludged in the cerebral cortical capilaries in a brain smear.

Treatment

Most cases of babesiosis resolve without any specific treatment. For ill patients, treatment is usually a two-drug regimen. The traditional regimen of quinine and clindamycin is often poorly tolerated; recent evidence suggests that a regimen of atovaquone and azithromycin can be equally effective . In life-threatening cases, exchange transfusion is performed. In this procedure, the infected red blood cells are removed and replaced with fresh ones.

Veterinary treatment of Babesiosis does not normally use antibiotics. In animals diminazene (Berenil), imidocarb or trypan blue would be the drugs of choice for treatment of Babesia canis rossi (Dogs in Africa), Babesia bovis, and Babesia bigemina (cattle in Southern Africa).

There is a vaccine that is effective against Babesia canis canis (dogs in the mediterranean region) but this is ineffective against Babesia canis rossi. Babesia imitans casuses a mild form of the disease that frequently resolves without treatment (dogs in South East Asia).

References

• Persing DH, Herwaldt BL, Glaser C; et al. (1995). "Infection with a babesia-like organism in northern California". N. Engl. J. Med. 332 (5): 298–303. PMID 7816065. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Krause PJ, Daily J, Telford SR, Vannier E, Lantos P, Spielman A (2007). "Shared features in the pathobiology of babesiosis and malaria". Trends Parasitol. 23 (12): 605–10. doi:10.1016/j.pt.2007.09.005. PMID 17988944. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
• Krause PJ (2003). "Babesiosis diagnosis and treatment". Vector Borne Zoonotic Dis. 3 (1): 45–51. doi:10.1089/153036603765627451. PMID 12804380.

External links

• "DPDx - Babesiosis". CDC. - Public domain source from which the first version of this article was derived.