Parasitology has just released a Special Issue from the 6^th International Workshop on Angiostrongylus and Angiostrongyliasis, Hilo, Hawai’i , USA, January, 2020

When a parasite is given the common name “rat lungworm” you know it is going to be a particularly unpleasant one. Indeed, these parasitic nematodes (Angiostrongylus cantonensis) are the causative agent of neuroangiostrongyliasis in humans, a disease characterised by eosinophilic meningitis.  However humans are accidental (or dead-end) hosts, meaning that we can get infected by the parasite but we cannot pass it on to another host, as (of now) the parasite hasn’t reproduced inside us, and so we essentially stop the life cycle.

Once you understand the natural life cycle of A. cantonensis the name “rat lungworm” makes a lot of sense, and you might realise that the parasite is perhaps even more nasty than you first imagined! Let’s start with the eggs, which hatch in the lung tissue of rats (now you know the reasoning behind the common name!) into L1 larvae (the first larval stage of five). L1 larvae move up the airways to the throat where they are swallowed by the rat, and make their way to the other end of the digestive tract within faeces. It seems that slugs and snails (intermediate hosts) can’t resist these bite-sized morsels, and will eat the rat faeces along with the A. cantonensis L1 larvae. Once within this slimy intermediate host, the larvae will develop from L1 to the infective L3 stage, where they wait for the slug or snail to be eaten by… a rat! Once the L3 larvae find themselves back in the definitive rat host they continue to mature and travel from the gut, to the bloodstream, the central nervous system and brain where they develop to the L5 stage, and from there travel to the heart and pulmonary arteries, where, as adults, the nematodes mate and lay eggs. Eggs then travel back to the lungs and develop to L1’s, and then are swallowed so the cycle can start over. Quite the journey for a worm that rarely grows to be bigger than a few centimetres in length!

Understanding the life cycle also helps us to understand how humans get infected and why we get sick. Often, human infection results from eating raw or undercooked slugs and snails, sometimes intentionally or by accidentally eating infected slugs hiding in uncooked produce, or from water in which slugs have drown and released infective L3’s! Luckily, there is some amazing research being done on A. cantonensis and the devastating diseases it can cause, and Parasitology has just released a Special Issue from the 6^th International Workshop on Angiostrongylus and Angiostrongyliasis, Hilo, Hawai`i , USA, January, 2020. We are so grateful to all of the authors that have contributed many different facets of research such as: how to  diagnosis and treat A. cantonensis infection, for example by detection of A. cantonensis antigens in cerebrospinal fluid or blood, DNA in slugs, evaluate clinical signs using MRI (magnetic resonance imaging) and the efficacy of different treatments including various anthelmintics, and finally this issue provides updated guidelines for the diagnosis and treatment of neuroangiostrongyliasis.

Because the nematode relies on multiple host species to complete its life cycle, research on rats, slugs and other animals is also vital. Manuscripts within the Special Issue give us greater insight into how A. cantonensis survive, reproduce, are transmitted, and infection of new hosts, for example dogs and Galliformes birds (chicken and Japanese quail). A. cantonensis larvae can escape from dead snails and slugs and go on to infect a new gastropod host, and in some places an astonishing 86% of Parmarion martensi (a species of semi-slug) can be infected! Up-to-date research on infection levels in the wild in both slugs/snails and rats are provided in such diverse geographic regions as the Phillipines, Hawai’i, and Florida. 

However, as two papers within the Special Issue highlight, we need to spread this knowledge so that people can understand how best to protect themselves from this parasite;  e.g. how we might be able to avoid infections in the first place by killing larvae that may be in our food, and an education program that is being employed on some of the Hawaiian Islands which has already gained positive feedback from participants. As a result of this program a sixth-grade class reported the arrival of P. martensi (that pesky semi-slug species that is a very competent host) in a new location, an important discovery that initiated community awareness and control efforts!

All 18 manuscript contributions to the special issue provided important and fascinating information on A. cantonensis and the infections they can cause. We are proud to showcase this valuable work on this parasite. Collectively, this body of literature makes huge strides in advancing our knowledge on this disease.