95
immunodeficient. In spleen-intact patients, parasitemia usually ranges from 1 to
20 percent, although parasitemia of 85 percent has been reported. Hemolytic
anemia and thrombocytopenia are frequent, and the urine may be dark.
Examination of blood smears has been the most useful diagnostic procedure. The
tetrad (Maltese-cross) forms of the parasite are typical, although the predominant
forms in most blood smears closely resemble the rings of Plasmodia. Difficulty in
distinguishing between the two organisms is avoided primarily because their
ranges do not appear to overlap. An indirect immunofluorescent antibody assay
(IFA) is available.
Quinine combined with clindamycin is the treatment of choice.
F. Infections with Multiple Organisms: The first reported fatal case of Lyme disease
occurred
in a patient who also had babesiosis. In a study from Block Island, RI,
sixteen of forty-six subjects with babesiosis also had B. burgdorfor infections. In
a study of 240 Long Island and Connecticut patients with Lyme disease, twenty-
six (11 percent) also had babesiosis. Co-infected patients had a greater incidence
of fatigue, headache, sweats, chills, anorexia, emotional lability, nausea,
conjunctivitis, and splenomegaly. Half of the co-infected patients were
symptomatic for three months or longer, but only seven (4 percent) of 184
patients with Lyme disease alone (and available for follow-up) had illnesses that
persisted that long. Co-infected patients also experienced more symptoms and a
more persistent illness than those with babesiosis alone.
Investigators who studied adult I.
scapularis ticks from Wisconsin, Massachusetts
(Nantucket Island),
and New York (Westchester County), collected between 1982 and
1995, found that between 2.2 percent and 26 percent were co-infected
with B. burgdorferi
and an agent resembling E. equi, the cause of HGE.. Simultaneous infections with two or
even three of these organisms should be anticipated.
G. Tularemia: Humans are highly susceptible to infection with the organism, which
occurs most often through the bite of an arthropod. Ticks are the most common
vector in the United States, particularly in the central and Rocky Mountain states,
where most infections occur. (Biting flies are responsible for many infections in
California, Nevada, and Utah.) The most commonly infected ticks are the Lone
Star tick (Amblyomma americanum), the dog tick (Dermacentor variabilis), and
the wood tick (Dermacentor andersoni).
After the bite of an infected arthropod, the incubation period averages about three
to five days, but the range is one to twenty-one days. After cutaneous inoculation,
F. tularensis multiplies at the local site and produces a papule. Ulceration follows
two to four days later. At this point, organisms spread locally to regional lymph
nodes and then may disseminate through the blood and lymphatics.
Six classic forms of the disease have been described--ulceroglandular, glandular,
oculoglandular, oropharyngeal, typhoidal, and pneumonic--based on clinical
presentation of the illness. These forms frequently overlap in individual patients.
