Cryptosporidium hominis is a microscopic parasite that causes the intestinal illness cryptosporidiosis, a cause of waterborne diarrheal disease worldwide. While several Cryptosporidium species can infect animals and humans, C. hominis almost exclusively infects people. The disease it causes can range from a mild, self-resolving illness to a severe condition, especially in individuals with weakened immune systems.
The Lifecycle and Transmission of the Parasite
The lifecycle of Cryptosporidium hominis begins when a person ingests the parasite in its dormant oocyst stage. These hardy oocysts can survive in the environment for long periods. Once swallowed, the oocysts travel to the small intestine and release four invasive sporozoites. These sporozoites attach to the cells lining the intestine to begin the infection.
Inside the intestinal cells, the sporozoites undergo asexual and sexual reproduction, which leads to the production of new oocysts. Two types of oocysts are formed: thick-walled oocysts, which are passed in the feces to infect others, and thin-walled oocysts, which can cause auto-infection and a more persistent illness. Oocysts are infective as soon as they are excreted, allowing for direct fecal-oral transmission.
Transmission occurs primarily through ingesting contaminated water, including from swimming pools, lakes, and drinking water. Contaminated food can also be a vehicle for transmission. A challenge in controlling the parasite is the high resistance of its oocysts to chlorine-based disinfectants used in water treatment. Person-to-person contact is another common route of transmission, particularly in settings like daycare centers.
Symptoms and Disease Progression
After an incubation period of two to ten days, an infected person develops symptoms. The most common symptom of cryptosporidiosis is profuse, watery diarrhea. This is often accompanied by stomach cramps, nausea, vomiting, and dehydration. A low-grade fever and weight loss can also occur.
In individuals with healthy immune systems, the illness is self-limiting, with symptoms lasting one to two weeks. It is possible for symptoms to appear in cycles, with periods of improvement followed by a return of diarrhea. Even after the diarrhea has stopped, some individuals may experience lingering symptoms like joint pain or fatigue.
The course of the disease is different for people with compromised immune systems, such as individuals with HIV/AIDS, cancer patients undergoing chemotherapy, or transplant recipients. In these patients, cryptosporidiosis can become a chronic, severe illness with diarrhea lasting for months. This prolonged diarrhea can lead to severe dehydration, malabsorption of nutrients, significant weight loss, and can be life-threatening. The infection may also spread beyond the intestines to other organs like the biliary tract, pancreas, or respiratory system.
Diagnosis and Medical Treatment
Diagnosing a Cryptosporidium hominis infection is done through laboratory analysis of a stool sample, which is examined under a microscope to identify the parasite’s oocysts. Special staining techniques, such as a modified acid-fast stain, are required to make the oocysts visible. Other diagnostic methods include antigen detection tests, like enzyme immunoassays (ELISA), and molecular methods such as polymerase chain reaction (PCR), which can detect the parasite’s genetic material.
For most people with healthy immune systems, treatment focuses on supportive care to manage symptoms. The primary objective is to prevent dehydration by drinking plenty of fluids, and oral rehydration solutions with electrolytes are often recommended. Antidiarrheal medications may be used to reduce the frequency of bowel movements.
The anti-parasitic drug nitazoxanide may be prescribed for individuals older than one year with healthy immune systems to reduce the duration and severity of diarrhea. Treatment for immunocompromised patients is more complex and focuses on improving their immune status, for example, through antiretroviral therapy for those with HIV. Nitazoxanide has not been shown to be consistently effective in this patient population.
Prevention and Household Control
Preventing the spread of Cryptosporidium hominis relies on good personal hygiene and water safety practices. Thorough handwashing with soap and water is necessary, especially after using the toilet, changing diapers, and before preparing or eating food. Alcohol-based hand sanitizers are not effective at killing Cryptosporidium oocysts.
To prevent waterborne transmission, avoid swallowing water while swimming in pools, lakes, or rivers. During community outbreaks, health officials may recommend boiling drinking water for at least one minute to kill the parasite. Using a point-of-use water filter certified by NSF/ANSI under Standard 53 or 58 for “cyst removal” is also effective.
Individuals diagnosed with cryptosporidiosis should take precautions to avoid infecting others. They should not use public swimming pools or recreational water venues for at least two weeks after their symptoms have completely resolved, as they can continue to shed oocysts. Careful cleaning and disinfection of surfaces that may have become contaminated with feces can also help control the spread within a household.