There are several
protozoan infections that cause relatively benign illness in normal individuals but result in severe disease manifestations in patients with
AIDS. These diseases include
Pneumocystis carinii pneumonia, CNS
toxoplasmosis,
cryptosporidiosis, and
isosporiasis.
Pneumocystis carinii pneumonia (PCP) caused by Pneumocystis carinii, is the most common
opportunistic infection in
AIDS. It is seen in more than 80% of individuals with this syndrome. Although historically classified as a protozoan, this organism shares many biochemical characteristics with fungi. The onset of PCP may be insidious, and
cough and
dyspnea are the most common presenting symptoms. Auscultation of the lungs is often unremarkable, but diffuse infiltrates are commonly seen on chest radiographs. The diagnosis of PCP can be confirmed by identifying the organism on specimens obtained by sputum induction or bronchoalveolar lavage. Trimethaprim-
sulfamethoxazole is the treatment of choice but is unfortunately associated with
leukopenia and
rash in many individuals. Both trimethaprim-
sulfamethoxazole and aerosolized
pentamidine are used prophylactically in patients at high risk for initial or relapsing
infection. The appropriate use of these agents has resulted in improved survival for
AIDS patients with PCP.
Toxoplasmosis, due to Toxoplasma gondii, affects the central nervous system in patients with
AIDS.
Headache is a common presenting symptom, and both
seizures and
paresis can occur. A diagnosis of
toxoplasmosis is strongly suspected in symptomatic individuals with ringed mass lesions noted on head CT. Patients with this condition are treated with a combination of
sulfadiazine,
pyrimethamine, and
folinic acid.
Cryptosporidiosis and
isosporiasis are coccidian protozoan diseases that can result in severe, acute, and chronic
diarrhea in immunocompromised individuals.
Cryptosporidiosis is the more common of the two and is caused by an unknown species of the genus crytosporidium.
Isosporiasis is due to
infection with Isospora belli.
Dehydration and
weight loss are a common result of
infection with either agent. A definitive diagnosis can be made by examining an
acid fast
stain of a diarrheal stool specimen and demonstrating oocysts that are specific for each of these organisms. Fluid replacement and general supportive care are essential in the treatment of both of these diseases.
Spiramycin is an unproven treatment modality that is often used in patients with
cryptosporidiosis.
Isosporiasis responds to initial
therapy with trimethaprim-
sulfamethoxazole, followed by prophylaxis with
pyrimethamine. The adoption of safe sexual practices that minimize fecal-oral contamination should decrease the future prevalence of these diseases and other enteric
parasitic infections.