Ascariasis is a common parasitic infection caused by the nematode (roundworm) Ascaris lumbricoides. It is prevalent in areas with poor sanitation and hygiene practices. The diagnosis of ascariasis is typically done through stool examination. Here is a detailed explanation of why stool test is the correct option for diagnosing ascariasis:

b) Stool test:
- Ascariasis is primarily diagnosed through a stool test, also known as a stool ova and parasite (O&P) examination.
- In this test, a stool sample is collected and examined under a microscope to identify the presence of Ascaris lumbricoides eggs or adult worms.
- The stool sample is processed using specialized techniques to concentrate and detect the eggs or worms.
- The eggs of Ascaris lumbricoides have a characteristic appearance, which helps in their identification.
- The presence of adult worms in the stool sample confirms the diagnosis of ascariasis.

a) Blood test:
- Blood tests are not typically used to diagnose ascariasis.
- Blood tests may be helpful in detecting certain complications associated with ascariasis, such as eosinophilia (increased eosinophil count) and elevated levels of IgE antibodies.
- However, these findings are not specific to ascariasis and can occur in other parasitic infections as well.

c) Widal test:
- The Widal test is a serological test used for diagnosing typhoid fever, not ascariasis.
- It detects antibodies against Salmonella typhi, the causative agent of typhoid fever.

d) Amniocentesis:
- Amniocentesis is a medical procedure used during pregnancy to collect amniotic fluid for various diagnostic purposes.
- It is not used for diagnosing ascariasis.

In conclusion, the correct option for diagnosing ascariasis is a stool test (stool O&P examination). This test allows for the identification of Ascaris lumbricoides eggs or adult worms in the stool sample. Blood tests, Widal test, and amniocentesis are not appropriate diagnostic methods for ascariasis.

Intestine infection so test by stool test.