Babesiosis is a malaria-like illness
caused by intraerythrocytic protozoa that are transmitted by the
bite of the same hard-bodied ticks (Ixodid) that transmit Lyme disease
and human granulocytic anaplasmosis.1-2 Babesia species
are parasites of mammals and birds that are currently classified
in the subphylum Apicomplexa, together with those organisms that
cause malaria (Plasmodium sp.) and toxoplasmosis
(Toxoplasma gondii). Only a few of the more than
90 species of Babesia cause disease in humans including, Babesia
microti and Babesia microti-like species
from the United States, Asia, and Europe, Babesia duncani (WA1)
from California and Washington State, Babesia divergens and Babesia
divergens-like species from Europe and the United States,
and Babesia venatorum (EU1) from Europe.2-3
Although babesiosis has long been recognized as an economically
important disease in livestock, the first human case was not described until
1957. Over the past 30 years, the epidemiology of the disease has
changed from a few isolated cases to the establishment of endemic
areas in southern New England, New York, and the upper Midwest,
and reports come from a wide geographic range in America, Africa,
Asia, and Europe.1-2 The incidence of babesial
infection is similar in children and adults (eFig.
babesiosis is transmitted in the northeastern United States by deer
ticks (Ixodes scapularis) that feed from infected
animal reservoirs (primarily the white-footed mouse, Peromyscus
leucopus).5 Nymphal ticks feed in the
late spring and summer, and those that are infected transmit B.
microti to rodents or man. Consequently, most human cases
of babesiosis occur in the summer. The white-tailed deer is an important
host of the deer tick. The recent increase in the deer population
is thought to be a major cause of the increased incidence of human
babesiosis, human granulocytic anaplasmosis, and Lyme borreliosis.
Rarely, babesiosis is acquired through blood transfusion or transplacental-perinatal
Age distribution of B. microti and B.
burgdorferi infection. The pink bars depict the age distribution
of subjects seropositive for B. microti, and the
blue bars depict the age distribution of subjects seropositive for B.
burgdorferi. There was no significant difference in the
percentage of subjects seropositive for either B. microti or B.
(From Krause PJ, Telford SR, Pollack RJ, et al.
Babesiosis: an underdiagnosed disease of children. Pediatrics.
The clinical manifestations of babesiosis range from subclinical
illness to fulminating disease resulting in death or prolonged convalescence.1-3 Symptoms
begin after an incubation period of 1 to 6 weeks from the beginning
of tick feeding. The unengorged I. scapularis deer
tick is only about 2 mm in length, so there is often no recollection
of a tick bite. Typical symptoms include intermittent
temperature to as high as 40°C (104°F) and one or more of the following: