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50 6 Malaria Parasites and Babesia

In its life cycle, merogony takes place in the vertebrate host and sporogony in the
invertebrate host. Man acquires infection by bite of the infected ticks. Sporozoites
present in the salivary glands of tick are introduced into human or other mammals.
Sporozoites transform to trophozoites in the circulation, which then invade the RBCs
and multiply asexually by binary fission. The organisms frequently occur in pairs or
in tetrads. Trophozoites are released when erythrocytes rupture and invade new
erythrocytes. It can be differentiated from malarial parasites by the absence of pig-
ments in the infected RBCs. Female ticks become infected by feeding on the infected
rodents’ blood which contains gametocytes. In the digestive tract of tick, the game-
tocytes undergo sexual development to produce sporozoites which then migrate to
the salivary glands. The sporozoite is the infective form for human. In humans, liver
is not involved in the life cycle of Babesia. Gametocyte and schizont stages are not
found in humans. Humans usually are dead-end hosts. However, human-to-human
transmission is well recognized to occur via contaminated blood transfusions.

Pathogenesis and Clinical Features

Haemolysis of the infected erythrocytes is primarily responsible for many clinical mani-
festations. The infection may be subclinical, self-limiting or acute, resembling malaria.
In acute disease, there is malaise, fatigue, fever, headache, chills, sweating, myalgia,
arthralgia and anorexia. Fever shows no periodicity. Mild hepatosplenomegaly and hae-
molytic anaemia have been reported. Severe babesiosis is associated with high parasi-
taemia. Fatality rate is higher among immunocompromised patients. Complications of
acute babesiosis are renal failure, disseminated intravascular coagulation (DIC), acute
respiratory distress syndrome (ARDS) and congestive cardiac failure (CCF).

Diagnosis

1. Microscopic examination
Absence of schizonts and gametocytes and presence of tetrads (maltese cross)
in peripheral blood smear.
2. Molecular diagnosis
PCR on blood.
3. Serodiagnosis
There are no serologic kits available.
4. Animal inoculation
Blood from suspected cases are inoculated into hamsters to be examined later
for infected RBCs.