The clinical syndrome seen with A. cantonensis is due to the intense inflammatory reaction of the dying parasites. Eosinophilic meningitis (EoM) remains the most common presentation of angiostrongyliasis. Headache is the most common symptom that can be associated with neck stiffness, nausea, and vomiting. Paresthesias and hyperesthesias can be associated with symptoms that can last for several weeks. Eosinophilic encephalitis (EoE) is rare but usually fatal due to late diagnosis. Rarely, ocular involvement can manifest with foreign body sensation and blurred vision from the anterior chamber and intravitreal invasion of larvae, respectively.[5][6][7]

CNS features of infection include new-onset severe headache resistant to NSAID therapy and paraesthesias (such as touch hypersensitivity, tingling, burning sensation). Shifting paresthesias are a notable characteristic along with migratory pain in the trunk and limbs (not in a dermatological distribution). CN VI or VII nerve palsy may occur. It is not clear why patients may also present with urinary retention. Before CNS symptoms become prominent, changes usually start with the GI tract. The incubation period for infection occurs over 1to 3 weeks (but can extend up to 6 weeks), and during this time, patients may develop nonspecific abdominal pain, nausea, and vomiting. This occurs due to the infiltration of the intestinal wall by the larva. They then circulate through the blood and ultimately penetrate the brain through the blood-brain barrier when the neurological symptoms start to occur. This period takes one to a few weeks to occur, and so patients may have a resolution of the initial GI symptoms and be asymptomatic during this period, or there may be the persistence of the GI symptoms. Emesis can also occur due to meningeal involvement. More nonspecific symptoms include lethargy, low-grade fever, difficulty sleeping, confusion. Children tend to have less prominent neurological findings and more gastrointestinal involvement. Physical exam should focus on a complete neurological and abdominal exam. 

Diagnosis of neuro-angiostrongyliasis is made of clinical history, suggestive signs, and symptoms and supporting laboratory findings. Clinical history should include a focus on travel to or from an endemic area, consumption of poorly cooked foods or raw vegetables contaminated with snail/slug components, crab, shrimp, etc. Although not confirmatory, CSF eosinophilia (usually exceeds 10%, can be as high as 70%) is required for the diagnosis in the right clinical setting. Eosinophilia in the CSF is defined as 10 or more eosinophils per microliter of CSF fluid or greater than 10% of total CSF leukocytes (with at least 6 in absolute count per microliter of fluid). CSF opening pressure and protein are usually elevated, with CSF leucocytosis typically ranging from 150-2000 cells/mm. Peripheral eosinophilia is often reported; however, it does not correlate well with CSF eosinophilia or the clinical course. The article editor has personally encountered and made the diagnosis by observing a larva coming out of the spinal needle with the CSF during lumbar puncture, quite a memorable experience.  Brain imaging with CT or MRI is generally not too helpful in making the etiological diagnosis.[8][9]

Serological immunoassays such as dot blot ELISA or western blot can aid in the diagnosis but are not widely available. PCR and real-time PCR based tests are reported to have good sensitivities, but again not as readily available.[10]. The important differential diagnosis to consider is gnathostomiasis, which is another cause of eosinophilic meningitis.  Gnathostomiasis usually presents with radicular pain, non-traumatic bloody or xanthochromic CSF, with brain imaging revealing SAH or intracerebral hemorrhage. Imaging may sometimes reveal myelitis, but this is not found in the case of A. cantonensis. The diagnostic immunoblot band is usually 29 kDa.

The severity and duration of clinical manifestations are variable and dependent on the parasitic burden. Most patients have spontaneous resolution of the symptoms with conservative measures. The goal is to decrease the meningeal inflammation and lower the intracranial pressure through the removal of the spinal fluid and symptomatic relief of headache. Administration of steroids (prednisolone or dexamethasone) to depress the inflammatory reaction has been associated with decreasing the duration of headache and requirement for serial CSF drainage.[11] Anti-helminthic medications were traditionally not recommended for the potential risk of an exaggerated inflammatory response to the release of antigens from dying parasites. Although the addition of anti-helminthic therapy to steroids has not shown benefit in the outcome of treatment compared to steroids alone, it is safe and should be considered in those patients with high parasite load.[9][12]

Ocular angiostrongyliasis has been reported in about 1% of all reported case reports. It occurs when the larva enters the anterior or posterior chamber. The exact mechanism of entry into the eye is unclear but has been thought to be secondary to travel along the retinal artery between the optic nerve and sheath. Usually, only 1 larva is present and symptoms include blurred vision, blindness, pain. Usually, eosinophilic meningitis is also present in these cases. Ocular involvement requires laser treatment to kill the larva before surgical removal. 

There are no official guidelines for treatment however on the premises of evidence-based medicine the following recommendations are followed. In Hawaii, a real-time PCR test can be performed on CSF fluid that detects DNA from A. cantonensis. If negative during early states of infection, this test and repeat LP should be done if strong suspicion is present. Serological testing against antibodies in the serum or CSF is not recommended. Albendazole if added may provide benefit but should be used in combination with steroids to dampen the intense inflammatory response created by the dying parasites. Careful attention should be paid to adequate glycemic control in this case in diabetic patients.

Other infections that can cause eosinophilic meningitis include gnathostomiasis and baylisascariasis. [15]Gnathostomiasis is associated with consuming undercooked fish, poultry, or snake meat. Baylisascariasis is caused by the consumption of parasite (Baylisascaris procyonis) eggs (usually in children by ingesting soil) usually transmitted in raccoon feces. Cystercicosis caused by Tinea solium or other diseases caused by lung flukes such as schistosomiasis, and paragonimiasis are other important differentials.  Coccidioidomycosis is also associated with eosinophilic meningitis. Non-infectious causes of eosinophilic leptomeningeal enhancement include non-Hodgkin lymphoma, myeloproliferative disorders, disseminated glioblastoma, and paraneoplastic manifestation from bronchogenic carcinoma. Drugs associated with eosinophilic meningitis include TMP-SMX, ciprofloxacin, ibuprofen, and intraventricular vancomycin and gentamicin.[13] Encephalopathy and neurological deficits have been reported to be associated with idiopathic hypereosinophilic syndrome. The most important point in the diagnosis is a high index of suspicion in patients who have likely been exposed to the nematode during the previous few weeks, which can extend up to 6 weeks prior. 

Prognosis is dependent on the timing of correct diagnosis as eosinophilic meningitis is rare and requires good clinical suspicion to suspect A. cantonensis as the causes as well as appropriate CSF findings. Sometimes the course of infection can be self-limiting, and other times depending on the disease burden may be fatal. There is an overall lack of national surveillance of this disease, and due to the limited diagnostic testing as well as poor general awareness among health care providers, it is difficult to quantify the outcomes.

Complications include death from eosinophilic meningitis or permanent blindness.  

Ocular angiostrongyliasis has been reported in about 1% of all reported case reports. It occurs when the larva enters the anterior or posterior chamber. The exact mechanism of entry into the eye is unclear but has been thought to be secondary to travel along the retinal artery along between the optic nerve and sheath. Usually, only 1 larva is present, and symptoms include blurred vision, blindness, pain. Usually, eosinophilic meningitis is also present in these cases.

Angiostrongyliasis has been associated with the consumption of the intermediate hosts of the Angiostrongylus cantonensis species. Local cases should be reported to public health to decrease further consumption of infected intermediate hosts and to contain the source. It is essential to raise public awareness of the undercooked consumption crabs, snails, slugs, prawns.

Since the risk of infection occurs from the ingestion of the vectors, then the ingestion of raw snails/slugs, crabs, shrimp should be avoided. Additionally, there can be accidental inclusion of the raw snail slug in uncooked foods such as salads. Care should be taken in food preparation and careful handwashing.  

A high index of clinical suspicion is most important in making the diagnosis of Angiostrongylus meningitis. The possible clinical exposure especially travels to endemic areas, followed by acute or subacute meningitis should raise suspicion. The presence of blood or CSF eosinophilia should point to the diagnosis.

To improve patient safety and outcome, integrated care by the healthcare team is very important. In order to make the correct diagnosis early to improve the prognosis, it requires a high index of suspicion by the managing physician and the neurologist. The infectious disease specialist may be able to provide a good list of differential diagnoses giving the clinical, blood, CSF, and imaging findings. They are also able to recommend the best diagnostic approaches and treatments. Finally, the nurses and therapists are the ones to help improve the outcome of the patients. This team approach is especially important, given the fact that Angiostrongylus meningitis is rare among developed nations.