Giardiasis

　　Cryptosporidium parvum belongs to the phylum Sarcodina, class Zoomastigophora, family Hexamitidae, order Diplomonadida, genus Giardia. In addition to Giardia lamblia, which is parasitic in humans, there are many species of Giardia that parasitize mammals, birds, amphibians, such as Giardia bovis, Giardia egui, and Giardia muris. Trophozoites are parasitic in the small intestine, especially in the duodenum, and can also be found in the gallbladder, liver, pancreas, and other organs. When the organisms parasitize the biliary tract system, they may cause cholecystitis or cholangitis. Symptoms such as upper abdominal pain, loss of appetite, liver enlargement, and fat metabolism disorders may occur.
　　It is generally believed that the incidence of Cryptosporidium parvum infection is related to multiple factors such as the virulence of the strain, the immune status of the host, and the symbiotic internal environment. Trophozoites adhere to the intestinal mucosal surface with their suckers, causing mechanical stimulation and injury that lead to mucosal inflammation. When the organisms multiply in large numbers, they can cover a large area of the intestinal mucosa, affecting the absorption of fats and fat-soluble vitamins and other substances. The organisms also compete with the host for nutrients in the lumen, and changes in the intestinal flora can lead to intestinal dysfunction to varying degrees. The organisms can cause lesions in the microvilli of the small intestine and lead to a lack of disaccharidases such as lactase and xylose, resulting in symptoms such as abdominal distension and poor lactose tolerance.

　　Patients with Cryptosporidium parvum infection may experience water and electrolyte imbalances, and may also cause systemic diseases such as anemia and malnutrition, growth retardation, and secondary lactose intolerance and vitamin deficiency.

　　The incubation period of Cryptosporidium parvum is generally 1-3 weeks, with an average of 9-15 days, and the clinical manifestations are mainly gastrointestinal symptoms. The typical symptoms of the acute phase are explosive diarrhea, watery stools with a foul odor, with a small amount of mucus, but usually without pus and blood. Patients often have symptoms such as loss of appetite, nausea, vomiting, abdominal distension, and belching. Abdominal pain is common, often in the upper and middle abdomen, and is colicky. Some patients have systemic symptoms such as low fever, chills, headache, fatigue, and decreased appetite. There are also cases where only oocysts are excreted without symptoms.

　　The acute phase lasts for several days. If not treated promptly, it may develop into subacute infection, mainly manifested by intermittent diarrhea, abdominal pain, and decreased appetite, which may last for several months.

　　The chronic phase is mainly manifested as recurrent episodes or persistent loose stools, mostly periodic short-term diarrhea, with loose stools floating with yellow froth on the surface, malodorous, and usually less than 10 times per day. Abdominal distension, belching, anorexia, nausea, but abdominal colic is rare. The course of the disease can last for several years, and in cases of Cryptosporidium parvum infection in children and severe infected individuals, long-term malabsorption can lead to emaciation, weight loss, developmental disorders, anemia, and other symptoms. When the organisms invade the gallbladder and bile ducts, patients may present with symptoms of cholecystitis and cholangitis, such as pain in the right upper abdomen or below the xiphoid process, nausea and vomiting, fever, and tenderness in the gallbladder area. When the lesions involve the liver, the main manifestations are pain in the liver area, liver enlargement with tenderness, and liver function damage. In addition, some patients may present with gastritis, appendicitis, and other conditions.

　　Strengthening water source hygiene management, paying attention to dietary hygiene, thoroughly treating patients with Giardiasis and asymptomatic cyst carriers, eliminating the vectors such as cockroaches and flies, doing fecal harmless treatment, maintaining normal immune function, checking and treating pets, controlling animal infectious sources, and other important measures are all important for preventing the occurrence or spread of Giardiasis.

　　In addition to the typical clinical manifestations of the patient, the diagnosis of Giardiasis is mainly made through laboratory examination of the pathogenic parasites.
　　1. Laboratory examination
　　1. Pathogen examination
　　Trophozoites can be found in fresh diarrhea stools, while cysts are mostly found in paste-like and formed stools. Trophozoites can be found directly in fecal saline smears; iodine staining can make cysts easier to identify. Concentration methods such as zinc sulfate floatation can improve the detection rate of cysts. Fecal examination should be carried out three times, and the positive rate can be increased to 97%. Duodenal drainage, small intestinal mucus, or biopsy tissue can all detect Giardia lamblia trophozoites.
　　2. Immunological tests: Immunological tests can be divided into two categories: detection of antibodies in serum and detection of fecal antigens.
　　(1) Detection of antibodies
　　Since the pure culture of Giardia lamblia was successfully established, due to the possibility of preparing high-purity antigens, the sensitivity and specificity of immunodiagnosis have been greatly improved. China has established two strains of Giardia lamblia culture, providing conditions for the development of immunodiagnosis in China. Enzyme-linked immunosorbent assay (ELISA) and indirect fluorescent antibody test (IFA) can be used to check patient serum antibodies, with the former reaching 75% to 81% positive and the latter reaching 66.6% to 90% positive.
　　(2) Detection of antigens
　　Enzyme-linked immunosorbent assay (ELISA) double sandwich method, dot enzyme-linked immunosorbent assay (Dot-ELISA), and counterflow immunoelectrophoresis (CIE) can be used to detect antigens in fecal dilutions. The positive rate of ELISA by double sandwich method can reach up to 92%, and Dot-ELISA can reach 91.7%, while CIE can reach 94%. The detection of fecal antigens can not only be used for diagnosis but also for evaluating efficacy.
　　3. Molecular biological diagnosis
　　In recent years, the ribosomal RNA (rRNA) gene product of Giardia lamblia has been detected using polymerase chain reaction (PCR), which can detect amplified copies equivalent to the amount of DNA in a trophozoite genome. Radioactively labeled chromosome DNA probes can also be used to detect trophozoites and cysts. Molecular biological methods have high specificity and sensitivity, thus offering broad application prospects.
　　Second, auxiliary examination
　　Abdominal ultrasound to understand liver and gallbladder conditions. X-ray chest film and electrocardiogram should also be performed.

　　The diet of patients with Giardia lamblia should mainly be light, increase the intake of high-quality protein, vitamins, and mineral elements to enhance their own immunity. While ensuring a nutritious diet, attention should be paid to dietary hygiene and boiled water should be consumed.

　　Patients with Giardia lamblia should be isolated according to enteric infectious diseases and dietary control. Antibiotics should be given in case of bacterial infection. Antipathogen drugs should be given to confirmed patients and those highly suspected of the disease. After thorough treatment, the absence of clinical symptoms or signs, as well as the absence of cysts in stool examination, indicates a cure.
　　1. Metronidazole
　　Metronidazole is the first-line drug for the treatment of Giardia lamblia. Adults 200mg/time, 3 times/d, for 5-7 consecutive days, efficacy can reach over 90%. Children 15-20mg/(kg·time), 3 times/d, for 5-7 consecutive days. Generally, after 3 days of medication, the original parasites in the stool can turn negative, and symptoms gradually disappear. Common side effects include a metallic taste in the mouth, nausea, fatigue, drowsiness, etc. Alcohol should be avoided during medication, and pregnant women and lactating patients should not use it.
　　2. Furazolidone
　　Adults 100mg/time, 3 times/d or 4 times/d, for 7 days; children 5-10mg/kg body weight, taken in 4 doses, for the same duration. Efficacy can reach about 80%.
　　3. Albendazole
　　Adults 250mg/time, 2 times/d; children 50-100mg, 2 times/d, for 3 consecutive days, efficacy can reach 90%-100%, albendazole is a promising anti-Giardia lamblia drug.
　　4. Praziquantel
　　Adults 600mg/d, 2 times/d, for 3 consecutive days. Alternatively, 20mg/kg body weight, 3 times/d, for 2 consecutive days. The efficacy of praziquantel treatment needs further research to be determined. Abroad, some people still use tinidazole (tinidazole), nimorazole (nimorazole), and in China, the extract of Sophora flavescens is used for the treatment of Giardia lamblia, with efficacy over 90%.