Doctors suspect meningitis or encephalitis caused by Angiostrongylus cantonensis when they see certain risky behaviors in a patient's medical history along with typical sypmtoms of the infection. These behaviors include eating slugs, snails, or possibly contaminated food and drinking water from unknown sources. The problem is, many cases of this infection go undiagnosed and untreated.

To make a definite diagnosis, doctors look for Angiostrongylus cantonensis larvae or their genetic information in the fluid around the brain and spinal cord, known as cerebrospinal fluid (CSF). However, the success rate of finding these parasites is quite low. So, doctors can also make a likely diagnosis based on the patient's medical history, symptoms, the number of certain immune cells called eosinophils in the CSF, and some immunological tests.

In most cases, a procedure called a lumbar puncture will be performed on patients suspected to have this infection. During this procedure, a small amount of CSF is taken from the lower spine with a thin needle. This can help not only in diagnosis but also in relieving headaches, which are common with meningitis. The CSF is then checked under a microscope for the presence of larvae and for an increased number of eosinophils, which often indicates a parasitic infection. However, finding larvae in the CSF confirms the infection in only about half of the cases, so additional tests are needed.

Immunological tests are based on how the body's immune system reacts to specific proteins from the parasite, called antigens. These reactions can be detected in blood samples. These tests are useful when CSF samples are not available, but they may not work well for diagnosing recent infections. For acute cases, tests that detect antigens directly in the CSF have been developed.

Molecular tests, which look for tiny bits of genetic information from the parasite, are even more accurate than immunological tests. However, they require specialized equipment and can be expensive. One of the goala of our project is to create new diagnostic tests that are as accurate as molecular tests but easier to use in hospitals.

In addition to these tests, doctors may also use CT and MRI scans to help with diagnosis. These scans can show changes in the brain that may be caused by the infection and help distinguish it from other brain infections.

So, diagnosing this infection involves a combination of medical history, laboratory tests, and imaging to ensure an accurate diagnosis and provide the right treatment.