Isospora Infection (Isosporiasis)

Isosporiasis is an infectious disease that is caused by a coccidian parasite known as the Isospora belli. The parasite impacts the epithelial cells in our small intestine. There are three different types of intestinal coccidia known to infect humans; the Isospora belli is the least common of the three.

The life cycle of the Isospora belli begins as oocysts that contain one or sometimes two sporoblasts. Upon excretion, the sporoblasts mature and split, secreting a cyst wall and turning into sporocysts. The sporocysts split and become four sporozoites per sporocyst. When oocysts containing sporocysts are consumed, infection occurs. In the small intestine, the sporocysts excyst, releasing sporozites that invade the small intestines’ epithelial cells, initiating schizogony. When the schizonts rupture, merozoites are released in order to invade more epithelial cells. Asexual reproduction continues in such a fashion. Trophozoites mature into schizonts that hold several merozoites. In about seven days, the development of male and female gametocytes occurs. When oocysts are expelled with the stool, fertilization occurs.

Humans and animals are impacted by the Isospora belli. Isosporiasis occurs all over the world, especially in subtropical and tropical locations. People with weak immune systems are especially vulnerable and there have been outbreaks within American institutions. The symptoms of Isosporiasis include cramping, diarrhea, and abdominal pain that can go on for several weeks. Symptoms may lead to weight loss and malabsorption. Immunodepressed individuals, children and infants can have severe diarrhea. It is possible that Eosinophilia will be present, which distinguishes the infection from other infections of the protozoan nature.

In order to diagnose Isosporiasis, microscopy is used to examine the oocysts. More than one stool exam may be required in order to find oocysts. Duodenal specimen exams via a string test or a biopsy can help if stool exams prove to be unhelpful. Oocysts become visible on wet mounting with bright-field microscopy, UV fluorescence, and DIC. A modified acid-fast stain will also work. Treatment for the infection requires a prescription medication, usually Trimethoprim-sulfamethoxazole.