Cryptosporidiosis

Cryptosporidiosis, or "crypto," is a parasitic disease caused by Cryptosporidium, a genus of protozoan parasites within the phylum Apicomplexa.

This disease primarily affects the distal small intestine and can also impact the respiratory tract. It is notable for causing watery diarrhoea and is particularly severe in immunocompromised individuals, such as those with HIV/AIDS. The primary mode of transmission is through the faecal-oral route, often via contaminated water.

Signs and Symptoms

Cryptosporidiosis can manifest in various forms: asymptomatic, acute, recurrent acute, and chronic. Symptoms typically appear 5–10 days after infection and can last up to 2 weeks in immunocompetent individuals. In immunocompromised people, symptoms are more severe and can persist longer.

Intestinal Cryptosporidiosis

Common symptoms include moderate to severe watery diarrhoea, low-grade fever, crampy abdominal pain, dehydration, weight loss, fatigue, nausea, and vomiting. Less common symptoms might include reactive arthritis, jaundice, and ascites.

Respiratory Cryptosporidiosis

Symptoms of respiratory tract involvement include nasal discharge, voice changes, cough, shortness of breath, fever, and hypoxaemia.

Cause

Cryptosporidium is a protozoan pathogen in the phylum Apicomplexa. The main species causing disease in humans are C. parvum and C. hominis. The parasite completes its life cycle within a single host, producing cyst stages that are excreted in faeces and transmitted via the faecal-oral route.

Pathogenesis

The parasite is intracellular but extracytoplasmic, attaching to the microvilli of epithelial cells in the small intestine. It can cause damage to the microvilli, leading to malabsorption and diarrhoea. Infected individuals excrete the most oocysts during the first week of infection. The immune system reduces the formation of Type 1 merozoites and the number of thin-walled oocysts, helping prevent autoinfection.

Diagnosis

Several diagnostic tests for cryptosporidiosis include microscopy, staining, and antigen detection. Microscopy can identify oocysts in faecal matter, often requiring multiple stool samples. Techniques like formalin-ethyl acetate concentration and zinc sulphate centrifugal flotation can concentrate the oocysts. Staining techniques such as acid-fast staining and Giemsa staining are also used. Antigen detection can be done through direct fluorescent antibody techniques and enzyme-linked immunosorbent assays (ELISA). Polymerase chain reaction (PCR) can identify specific species of Cryptosporidium.

Prevention

Preventing cryptosporidiosis involves avoiding contaminated water and practising good hygiene. Boiling water for at least one minute or using filters with pore sizes not greater than 1 micrometre can decontaminate water. People with cryptosporidiosis should avoid swimming in communal areas and stay away from immunosuppressed individuals. In the US, doctors and labs must report cases to local health departments, which then report to the Centres for Disease Control and Prevention.

Treatment

Immunocompetent Individuals

In immunocompetent individuals, cryptosporidiosis typically resolves on its own within two weeks. Treatment primarily involves fluid rehydration, electrolyte replacement, and antimotility agents. Nitazoxanide is the only antiparasitic drug with proven efficacy in these individuals.

Immunocompromised Individuals

In immunocompromised individuals, cryptosporidiosis can be severe and persistent. Treatment involves improving immune status using highly active antiretroviral therapy and continued antiparasitic medication. Drugs like nitazoxanide, paromomycin, and azithromycin are used, though they have limited efficacy. Research is ongoing into molecular-based immunotherapy and synthetic isoflavone derivatives.

Epidemiology

Cryptosporidiosis is a global disease, causing a significant proportion of waterborne diseases attributed to parasites. It is more prevalent in developing countries, affecting children aged 1 to 9 most commonly. In the United States, about 30% of adults have contracted the infection at some point in their lives.

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Self-assessment MCQs (single best answer)

What is the primary mode of transmission for Cryptosporidiosis?

Which of the following is a common symptom of intestinal cryptosporidiosis?

Which species of Cryptosporidium is most commonly associated with human infections?

What is the most effective way to decontaminate water to prevent cryptosporidiosis?

In which part of the body does Cryptosporidium primarily cause infection?

What diagnostic technique uses formalin-ethyl acetate concentration for detecting cryptosporidiosis?

What treatment is recommended for immunocompetent individuals with cryptosporidiosis?

Which of the following is a symptom of respiratory cryptosporidiosis?

What is a major risk factor for severe cryptosporidiosis?

What is the recommended preventive measure for people with cryptosporidiosis to avoid spreading the infection?