Angiostrongyliasis
Angiostrongyliasis is an infection by a nematode from the Angiostrongylus genus of kidney and alimentary tract roundworms. For example, infection with Angiostrongylus cantonensis can occur after consuming raw Giant African land snails, Great Grey Slugs, or other molluscs.
In humans, Angiostrongylus is the most common cause of eosiniphilic meningitis.[1] Frequently the infection will resolve without treatment or serious consequences, but in cases with a heavy load of parasites the infection can be so severe it can cause permanent damage to the CNS or death.[2]
Early symptoms
Infection first presents with severe abdominal pain, nausea, vomiting, and weakness, which gradually lessens and progresses to fever, and then to CNS symptoms and severe headache and stiffness of the neck.
Severe/CNS infection
CNS symptoms begin with mild cognitive impairment and slowed reactions, and in a very severe form often progress to unconsciousness.[3] Patients may present with neuropathic pain early in the infection. Eventually severe infection will lead to ascending weakness, quadriparesis, areflexia, respiratory failure, and muscle atrophy, and will lead to death if not treated. Occasionally patients present with cranial nerve palsies, usually in nerves 7 and 8, and rarely larvae will enter ocular structures.[4] Even with treatment, damage to the CNS may be permanent and result in a variety of negative outcomes depending on the location of the infection, and the patient may suffer chronic pain as a result of infection.[3]
Eye invasion
Symptoms of eye invasion include visual impairment, pain, keratitis, and retinal edema. Worms usually appear in the anterior chamber and vitreous and can sometimes be removed surgically.
The parasite is rarely seen outside of endemic areas, and in these cases patients generally have a history of travel to an endemic area.
Transmission
Transmission of the parasite is usually from eating raw or undercooked snails or other vectors. Infection is also frequent from ingestion of contaminated water or unwashed salad that may contain small snail and slugs, or have been contaminated by them. Therefore it is very important to avoid raw snails, wash and cook vegetables thoroughly, and avoid open water sources that may be contaminated.
Reservoirs
Rats are the definitive host and the main reservoir for A. cantonensis, though other small mammals may also become infected. While angiostrongylus can infect humans, humans do not act as reservoirs since the worm cannot reproduce in humans and therefore humans cannot contribute to their life cycle.[2]
Vectors
A. cantonensis has many vectors, with the most common being several species of snails, including the giant African land snail (Achatina fulica) in the Pacific islands and snails of the genus Pila in Thailand and Malaysia. The golden apple snail, A. canaliculatus, is the most important vector in areas of China.[3] Freshwater prawns, crabs, or other paratenic, or transport, hosts can also act as vectors.[2]
Diagnostic tests
Diagnosis of Angiostrongyliasis is complicated due to the difficulty of presenting the angiostrongylus larvae themselves, and will usually be made based on the presence of eosiniphilic meningitis and history of exposure to snail hosts. Eosiniphilic meningitis is generally characterized as a meningitis with >10 eosiniphils/μL in the CSF or at least 10% eosiniphils in the total CSF leukocyte count.[4] Occasionally worms found in the cerebrospinal fluid or surgically removed from the eye can be identified in order to diagnose Angiostrongyliasis.
Lumbar puncture
Lumbar puncture should always be done is cases of suspected meningitis. In cases of eosiniphilc meningitis it will rarely produce worms even when they are present in the CSF, because they tend to cling to the end of nerves. Larvae are present in the CSF in only 1.9-10% of cases.[3] However, as a case of eosiniphilic meningitis progresses, intracranial pressure and eosiniphil counts should rise. Increased levels of eosinophils in the CSF is a trademark of the eosiniphilic meningitis.[3]
Brain imaging
Brain lesions, with invasion of both gray and white matter, can be seen on a CT or MRI. However MRI findings tend to be inconclusive, and usually include nonspecific lesions and ventricular enlargement. Sometimes a hemorrhagic, probably produced by migrating worms, is present and of diagnostic value.
Serology
In patients with elevated eosiniphils, serology can be used to confirm a diagnosis of Angiostrongylias rather than infection with another parasite.[1] There are a number of immunoassays that can aid in diagnosis, however serologic testing is available in few labs in the endemic area, and is frequently too non-specific.
Some cross reactivity has been reported between A. cantonensis and trichinosis, making diagnosis less specific.
The most definitive diagnosis always arises from the identification of larvae found in the CSF or eye, however due to this rarity a clinical diagnosis based on the above tests is most likely.
Management and therapy
Treatment of angiostrongyliasis is not well defined, but most strategies include a combination of anti - parasitics to kill the worms, steroids to limit inflammation as the worms die, and pain medication to manage the symptoms of meningitis.
Anti-helminthics
Anti-helminthics are often used to kill off the worms, however in some cases this may cause patients to worsen due to toxins released by the dying worms. Albendazole, ivermectin, mebendazol, and pyrantel are all commonly used, though albendazole is usually the drug of choice. Studies have shown that anti-helminthic drugs may shorten the course of the disease and relieve symptoms. Therefore anti-helminthics are generally recommended, but should be administered gradually so as to limit the inflammatory reaction.[3]
Anti-inflammatories
Anti-helminthics should generally be paired with corticosteroids in severe infections to limit the inflammatory reaction to the dying parasites. Studies suggest that a two week regimen of a combination of mebedizole and prednisolone significantly shortened the course of the disease and length of associated headaches without observed harmful side effects.[6] Other studies suggest that albendazole may be more favorable, because it may be less like to incite an inflammatory reaction.[7] The Chinese herbal medicine long-dan-xie-gan-tan (LDGXT) has also been shown to have a similar anti inflammatory effect, and in mild cases may be used alone to relieve symptoms while infection resolves itself.[7]
Symptomatic treatment
Symptomatic treatment is indicated for symptoms such as nausea, vomiting, headache, and in some cases, chronic pain due to nerve damage or muscle atrophy.