Giardia Test

Giardia is a single-celled, flagellated protozoan that lives in the small intestine. It has two forms. The cyst is a tough, dormant shell that survives in the environment and transmits infection through contaminated water, food, or hands. The trophozoite is the active feeding form that attaches to the lining of the small intestine. Attachment can flatten the intestinal microvilli and disrupt enzymes needed for nutrient absorption, which is why malabsorption and weight loss are common in symptomatic cases. After ingestion of cysts, symptoms usually start within one to two weeks and range from none at all to watery, foul-smelling diarrhea, bloating, abdominal cramps, gas, and fatigue. In children, repeated or prolonged infections can impair growth and cognition. After the acute illness resolves, some people develop post-infectious irritable bowel syndrome (IBS) or lingering fatigue.

Giardia circulates globally. Prevalence is higher where sanitation is limited, but outbreaks also occur in high-income regions, often linked to drinking water, recreational water, or childcare settings. Humans and many animals can carry Giardia; while most human infections are human-to-human in origin, animal-to-human transmission can occur. People with impaired immunity, such as those with common variable immunodeficiency, often have more persistent disease.

Diagnosis uses stool testing. Microscopy can identify cysts or trophozoites but misses cases when parasite numbers are low. Antigen detection tests identify parasite proteins and improve sensitivity. Polymerase chain reaction (PCR) detects Giardia DNA and is the most sensitive option, often included in multiplex gastrointestinal panels; collecting stool on more than one day increases yield because shedding can be intermittent.

Treatment typically starts with a nitroimidazole (metronidazole or tinidazole). Because drug resistance and treatment failures are increasingly reported, second-line or combination regimens may be needed in refractory disease. For prevention, emphasize safe drinking water, careful hand hygiene, thorough washing of produce, and avoiding swallowing water during recreational activities. For longevity-minded readers: prompt, accurate diagnosis and complete treatment reduce the risk of post-infectious IBS and help protect long-term gut function.