Sporazoans

Question 1

Plasmodium species

Answer 1

*Malaria
2010: 655,000 deaths worldwide.
P. falciparum (15 percent of all malaria cases); P. vivax (80 percent); three other species.
Parasite transmitted to humans through bite of a female Anopheles mosquito. Sporozoans reproduce asexually in human cells. Sexual reproduction occurs in the mosquito, where new spores (sporozoites) are formed.
Pathology and clinical significance: Plasmodium sporozoites are injected into the bloodstream, where they rapidly migrate to the liver; in liver, form cyst-like structures containing thousands of merozoites. Release = merozoites invade RBCs; eventually, the infected RBCs rupture, releasing merozoites that can invade other erythrocytes. RBC lysis = anemia. anemia. Infection can lead to capillary obstruction and death.

2. Diagnosis and treatment: Detection of the parasite inside RBCs. Giemsa stained blood smears. Determining the species involved is important in planning a course of therapy. Serologic tests are usually too slow for diagnosis of acute disease. Drug treatment is determined by the Plasmodium species that is causing the infection.

Question 2

Toxoplasma gondii

Answer 2

*Toxoplasmosis
Intracellular sporozoan, distributed worldwide. Infects all vertebrate species, although the definitive host is the cat.
Humans can become infected by the accidental ingestion of oocysts present in cat feces, by eating raw or undercooked meat, congenitally from an infected mother, or from a blood transfusion.
Rapidly growing tachyzoites in body fluids in early, acute infections, and slowly growing bradyzoites contained in cysts in muscle and brain tissue and in the eye. Tachyzoites directly destroy cells, whereas bradyzoites released from ruptured tissue cysts cause local inflammation, necrosis.
Healthy hosts: infections can be asymptomatic. Infections can be very severe in immunocompromised individuals, who may also suffer recrudescence (relapse) of the infection. Congenital infections can also be severe, resulting in stillbirths, brain lesions, and hydrocephaly, and they are a major cause of blindness in newborns.
Diagnosis: Initially, detection of parasites in tissue specimens. Now with commercial diagnostic kits, serologic tests to identify toxoplasma (including tests for Toxoplasma-specific immunoglobulin (Ig) G and IgM)
Management: Antifolate drug pyrimethamine, given in combination with sulfadiazine. For patients who can not receive sulfa drugs, clindamycin can be added to pyrimethamine.

Question 3

Cryptosporidium species

Answer 3

*Cryptosporidiosis
Intracellular parasite.
Inhabits the epithelial cells of the villi of the lower small intestine.
Source = feces of domestic animals, and farm run-off (contamination of
drinking water).
Asymptomatic to mild cases are common. However, in immunocompromised individuals, infection may be severe and intractable, although paromomycin has provided some improvement. Diagnosis is made by acid-fast staining of the tiny (4 to 6 μm) oocysts in fresh stool samples.