Page 98 - parasitology for medical and clinical laboratoryprofessionals

78 CHAPTER 4

Surra Transplacental West Nile virus
Tabanid flies Triatomid Wright-Giemsa stain
Trachoma Trypanosomiasis

BABESIOSIS Morphology

Organisms of the genus Babesia is a parasite that is The organism may be either a round- or rod-shaped
the causative agent of a somewhat rare disease that oc- protozoal parasite that is often characterized by a tet-
curs most frequently in the New England section of the rad configuration (Maltese cross). These parasites of
United States. The infection is most often self-limiting the genus Babesia are found as intracellular inclusions
but may become quite severe in asplenic (those without of the red blood cells and are found in the phylum
the spleen organ) and elderly whose immune systems are Apicomplexa (Figure 4-1). Unlike a number of other
diminished but rarely result in fatalities among the vic- protozoal organisms, this organism lacks organs for
tims. Many different Babesia species exist throughout motility such as amoeboid pseudopodia, cilia, or fla-
the world and several of these can infect humans. Babe- gella. One species of Babesia, called B. bigemina, has
siosis, the disease caused by infection with Babesia, is gained notoriety as the first parasitic disease in which
most common in New York (specifically, Long Island), a vector (carrier of the organism) was identified and
Martha’s Vineyard, and Nantucket, but fatalities are rarely described. The disease may have been discovered in the
recorded in humans. Although more than 100 species of late 1880s in diseased cattle herds from Texas, some of
Babesia exist across a large geographic span, only a small which may have been sold to other parts of the country,
number of species have been implicated in the majority but most of the general knowledge of human infection
of diseases known to affect humans. The causative agent has occurred in the past few decades.
of babesiosis varies by species according to geographic
regions that support the various parasites. Symptoms
In the United States, human infections with Babe-
sia species are almost exclusively due to Babesia microti. After an incubation period of a few weeks (but sometimes
The disease is found mostly in the northeastern states, after a couple of months), a febrile anemia may occur.
including some offshore islands and coastal areas. Only The initial symptoms are headache, general malaise with
a few documented cases in the midwestern states as well
as in California and Washington State have occurred,
leading to speculation that the disease is spreading and
may soon be prevalent throughout all areas of the United
States. Several cases have been reported in medical lit-
erature related to infections acquired from blood trans-
fusions in which the blood donors had lived in or had
traveled to an area endemic for the disease. All of these
cases have occurred in the United States with the ex- Source: Centers for Disease Control and Prevention (CDC)
ception of one Canadian patient who received blood
from a donor who became infected while in the United
States, and a single case reported in Japan. The rate of
acquiring B. microti from a unit containing red cells from
an infected donor has been estimated to be one in sev-
eral hundred to almost two thousand in endemic areas. FIGURE 4-1 Conventional “tetrad” configuration of
Although it is rare to find cases of transmission to fetuses these Babesia sp. trophozoites, which resemble
in utero, apparently a few incidences have occurred. P. falciparum