Following the resolution of diarrhea, symptoms can reoccur after several days or weeks due to reinfection. The likelihood of re-infection is high in immunocompromised adults, and low in those with normal immune systems.In immunocompetent individuals, cryptosporidiosis is primarily localized to the distal small intestine and sometimes the respiratory tract as well. In immunocompromised persons, cryptosporidiosis may disseminate to other organs, including the hepatobiliary system, pancreas, upper gastrointestinal tract, and urinary bladder; pancreatic and biliary infection can involve acalculous cholecystitis, sclerosing cholangitis, papillary stenosis, or pancreatitis. Intestinal cryptosporidiosis
Common signs and symptoms of intestinal cryptosporidiosis include:

Moderate to severe watery diarrhea, sometimes contains mucus and rarely contains blood or leukocytesIn very severe cases, diarrhea may be profuse and cholera-like with malabsorption and hypovolemia
Low-grade fever
Crampy abdominal pain
Dehydration
Weight loss
Fatigue
Nausea and vomiting – suggests upper GI tract involvement and may lead to respiratory cryptosporidiosis
Epigastric or right upper quadrant tendernessLess common or rare signs and symptoms include:

Reactive arthritis (may affect the hands, knees, ankles, and feet)
Jaundice – suggests hepatobiliary involvement
Ascites – suggests pancreatic involvement

Respiratory cryptosporidiosis
Symptoms of upper respiratory cryptosporidiosis include:

Inflammation of the nasal mucosa, sinuses, larynx, or trachea
Nasal discharge
Voice change (e.g., hoarseness)Symptoms of lower respiratory cryptosporidiosis include:

Cough
Shortness of breath
Fever
Hypoxemia

Reason
Cryptosporidium is a genus of protozoan pathogens which is categorized under the phylum Apicomplexa. Other apicomplexan pathogens include the malaria parasite Plasmodium, and Toxoplasma, the causative agent of toxoplasmosis. A number of Cryptosporidium infect mammals. In humans, the main causes of disease are C. parvum and C. hominis (previously C. parvum genotype 1).
Antibodies in the serum of humans and animals infected with Cryptosporidium parvum react with several antigens, one of which is a 15 kDa protein (CP15) located on the surface of the organism. This protein is a good candidate for use as a molecular vaccine because previous studies have shown that a monoclonal antibody to CP15 confers passive immunity to mice. Currently, there is no vaccine or completely effective drug therapy against Cryptosporidium parvum in HIV/AIDS individuals.A summary of discoveries presented at the most recent (June 2019) international symposium on Cryptosporidium has been published in 2020. Other animals
The most important zoonotic reservoirs are cattle, sheep and goats. In addition, in recent years, cryptosporidiosis has plagued many commercial leopard gecko breeders. Several species of the Cryptosporidium family (C. serpentes and others) are involved, and outside of geckos it has been found in monitor lizards, iguanas and tortoises, as well as several snake species. Notable cases
Before 2000
In 1987, 13,000 people in Carrollton, Georgia, United States, became ill with cryptosporidiosis. This was the first report of its spread through a municipal water system that met all state and federal drinking water standards. In 1993, a waterborne cryptosporidiosis outbreak occurred in Milwaukee, Wisconsin, US. An estimated 403,000 people became ill, including 4,400 people hospitalized.