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Organisms Borne by Ticks and Other Vectors 237

also experienced significant numbers of cases of babesio-
Source: Centers for Disease Control and Prevention (CDC) are both intra-erythrocytic parasites (dwell inside the red
sis in recent years. It is sometimes called the “malaria of
the Northeast” because babesiosis and human malaria

blood cells) and both may eventually cause the destruc-
tion of red blood cells and both are caused by a single-
celled protozoan. And along with Babesia microti, other
species of Babesia infect people on continents other than
North America. These related species of Babesia cause
similar illnesses in both humans and animals in a number
of countries other than the United States.
But contrary to the Plasmodium genus of para-
sites that cause malaria, the Babesia species lack an exo-
FIGURE 11-13 Babesia microti in blood smear, an
erythrocytic phase, one in which stages of the life cycle
intracellular parasite of red blood cells; note the clump
occur outside the red blood cells as occurs for malaria
of platelets to the left of the infected RBC
in the mosquito vector. Therefore, in the liver involve-
ment found in malaria, of which there are four major
parasite called a protozoan that is an intracellular para- human varieties, significant jaundice may exist due to de-
site that infects the red blood cells, as does the organ- stroyed red blood cells. Jaundice is usually not found in
ism Plasmodium that produces malaria (Figure 11-13). B. microti infections to the extent that malaria is. It has
Following the infection called trypanosomiasis, also not been definitively documented that there are sig-
caused by a blood parasite, Babesia organisms are nificant cases of Babesia species that occur in malaria-
thought to be the second most common blood parasites endemic areas. If this were the case the misdiagnosis of
of mammals. In addition, these organisms contribute to a malaria, of the genus Plasmodium, could easily be made
major impact on the health of domestic animals in areas in cases of babesiosis. In addition, another major differ-
that do not experience a severe winter season. ence lies in the fact that malaria is spread exclusively by
Babesiosis infections are more common in animals a particular species of mosquito, that of the Anopheles
than in humans but human cases have been reported in mosquito, rather than by a tick vector. The range of geo-
certain parts of the United States. And although human graphic regions where one species of organism is found
babesiosis is uncommon, reported cases have risen re- might not be conducive to the requirements for survival
cently, presumably because of an expanded medical of the other disease agent. However, Lyme disease and
awareness. The locations in which babesiosis has been babesiosis could occur concurrently because the tick
reported are approximately the same as those where species known to be vectors of the two diseases may be
Lyme disease is also endemic. For the transmission of found in close proximity.
babesiosis, a vector-borne illness usually transmitted by Cases of babesiosis have also been reported
Ixodid ticks, the deer tick typically carries the parasite over a wide area of Europe. Most countries of Europe
that causes this illness. Babesia microti is transmitted by have experienced at least some evidence of the illness.
the same tick vector, Ixodes scapularis, as are Lyme dis- The disease in Europe, as is the case in North America,
ease and ehrlichiosis, and may occur in conjunction with is due to infection of the Babesia genus of which Babesia
these other diseases. In endemic areas, B. microti may divergens is the most common species found. In the
also be transmitted through blood transfusions as the or- United States, B. microti is the species most commonly
ganisms could possibly survive the testing and the stor- associated with human disease but there are at least some
age required for preparing bags of blood for transfusion. cases in this country also attributed to Babesia duncani.
In North America, the illness is prevalent in the Cases of babesiosis have also been observed in both
coastal areas of Connecticut, New Jersey, and on islands North and South Korea.
off the coasts of New York and Massachusetts including Some people, especially healthy people younger than
eastern Long Island and its barrier island, Fire Island. the age of 40, often may have few if any noticeable symp-
But the states of Wisconsin, Georgia, and California have toms upon infection. Others may present with symptoms