Babesiosis

  Babesiosis 

 P K Ghatak,MD

Babesiosis is a parasitic infection transmitted to humans by a tick.

In 1888 Viktor Babes in Romania detected the parasite from the blood of the infected cattle. Humans are accidental victims. In the USA the main organism is Babesia microti, however, B. divergens, B. cressa, B. ventorum, and B. duncan species can occasionally cause illness.

The vector is a tick, Ixodes scapulars. It usually feeds on white footed mouse and other small animals.

At risk of Babesiosis :

The people in the coastal areas of the Northeastern states and the Great Lake states are mostly at risk of contacting Babesia and in recent years an increased in Babesiosis cases have been reported.

The parasite:

Babesia microti is a unicellular organism, lives in the RBCs of vertebrates. Humans are accidental victims. At a given time several forms of the parasites are seen inside the RBCs, Each one measures 2 x1.5 micrometers, usually ring-shaped but other forms are rods, pyriform, motile amoeba like and a characteristic Maltese form are also present.

The reservoir of parasites:

The usual animal is the white-footed mice, but other mammals are also act as reservoirs.

The vector:

The deer tick - Ixodes scapulars.

How human infection occurs:

In outdoor work or recreational activities, when people are not properly protected can get deer licks on legs, head and other expose areas of the body. As the tick feeds on the blood, the wound gets contaminated with the saliva of the tick, containing the parasites.

In unusual circumstances, contaminated blood transfusion can infect recipients. Still rarely, babies are infected in utero via the placenta. The incubation period is 1 to 4 weeks. 

Diagnosis:

The diagnosis of Babesiosis is difficult. Unless the healthcare provider has a high degree of suspicion of this illness, the disease can go undetected for a prolonged time.

Detecting ring form of the parasite is not easy from the artifacts and malaria parasites even with careful examination of Giemsa stained blood smears. A Maltese Cross shaped form of the parasite inside the RBC is diagnostic. The PCR test for parasite antigen in blood is diagnostic.

Treatment:

A combination of Atovaquone and Azithromycin for 7 to 10 days. Severely ill patients with higher parasitemia are treated with Clindamycin IV and Quinine by mouth for 7 to 10 days. Exchange transfusion may be required. Longer period of therapy may be required.

Many patients may develop significant adverse effects; in others, one or both combinations proved to be adequate to eliminate the parasite.

A brief description of the life cycle of Babesia microti:

The parasite has two multiplication cycles- (a)budding and (b) sexual reproduction: and needs two hosts – a tick and a mammal.

The deer ticks lay eggs on the grasses and vegetation. In the spring, these eggs hatch. The young ticks are promptly infected by Babesia. Inside the adult ticks, the parasites multiply by asexual methods. These young forms are transmitted to small animals or humans by the adult ticks during their bloody meals. In the RBCs of mammals, the parasites multiply and transform to other shapes, and some parasites change themselves into male and female units. And waits for an opportunity to be transferred to ticks at the next feeding time of another tick. Inside the ticks, the sexual units mate and reproduce many young parasites. And the cycle repeats.

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