A 30 year old veterinarian visits her obstetrician for a first-trimester prenatal check-up. She has no complaints.Routine physical exam is significant only for mild cervical lymphadenopathy. She is prescribed spiramycin but is noncompliant. Her baby is born with hydrocephalus and cerebral calcifications. Which of the following organisms is most likely responsible?
Humans become infected with Toxoplasma gondii by ingesting cysts in contaminated food or through contact with cat feces. The veterinarian in question was therefore paicularly at risk of infection. T. gondii is especially hazardous in pregnant women because the organism can be transmitted to the fetus through the placenta. (It is pa of the ToRCHeS group of congenital infections;Toxoplasma, Rubella, CMV, Herpes/HIV, Syphilis). Since infected mothers are usually asymptomatic, cases often go unnoticed. Occasionally, patients present with cervical lymphadenopathy, as did the veterinarian, and require treatment to prevent complications in the fetus. Though newborns are also often asymptomatic, they are at risk for developing the classic triad of chorioretinitis (at bih or later in life), hydrocephalus, and cerebral calcifications. Note that T. gondii is also a common cause of CNS infections (e.g., encephalitis) in HIV-positive patients. Isospora belli (choice A) is an intestinal protozoan that causes watery diarrhea, paicularly in the immunocompromised. Fecal-oral transmission of oocysts allows invasion of small intestinal mucosa, destroying the brush border. Leishmania donovani (choice B) causes kala-azar (visceral leishmaniasis), which is characterized by fever, weakness, weight loss, splenomegaly, and skin hyperpigmentation. It is prevalent in regions of the Mediterranean, Middle East, Russia, and China. The vector is the sandfly. Plasmodium vivax (choice C) causes malaria and is transmitted by the female Anopheles mosquito, which introduces sporozoites into the blood. These differentiate into merozoites that destroy erythrocytes. Splenomegaly ensues. Other species of this organism also cause malaria: P. malariae and P. falciparum (which causes a more severe form of the disease). Note that sickle cell trait confers resistance to this disease. Ref: Ray C.G., Ryan K.J. (2010). Chapter 50. Sporozoa. In C.G. Ray, K.J. Ryan (Eds),Sherris Medical Microbiology, 5e.
Isospora belli
Leishmania donovani
Plasmodium vivax
Toxoplasma gondii