Introduction.
Human angiostrongyliasis is an infection caused by a nematode parasite of rats. The tiny parasitic roundworm Angiostrongulus cantonensis (pronounced an-gee-o-stron-guh-luss can-tun-en-sis) is commonly called the rat lungworm.
The mature, adult form of the nematode is found only in rats.

The rat lungworm (Nematoda), Angiostrongylus cantonensis, causes neurological disease in humans and several fatalities have occurred in Australia (see review in Prociv et al. 2000).
It is of increasing concern due to the continuing expansion of its geographical range which now encompasses much of Southeast Asia, Melanesia, Polynesia, eastern Australia, parts of Africa, India, the Caribbean and the south-eastern United States of America (USA).⁽²⁾

Naturally occurring, non-human infections were first recognised in dogs in Brisbane in 1972 and in Sydney in 1989 and 1991 (Collins et al 1992).

In the city of Brisbane, the first human infections probably occurred in 1959. From the 1970s, increasing numbers of autochthonous infections have been reported along the central east coast of the continent (southeast Queensland and northern New South Wales), involving humans, rats, dogs, horses, flying foxes and marsupials.

In 1989 the parasite was discovered in Sydney, almost 1,000 km to the south, in dogs. In that city, it has since been diagnosed as a cause of neurological disease in increasing numbers of dogs, flying foxes, marsupials and zoo primates.
Presumably, these infections resulted from the ingestion of snails or slugs, and it seems that virtually all species of native and exotic terrestrial molluscs can serve as intermediate hosts.

The first reported case of human angiostrongyliasis ( rat lungworm infection ) acquired in Sydney in 2001. It is not known how the parasite was introduced to this continent, or how it has spread over such an extensive territory, although eventually its range could encompass the entire east coast, and potentially other regions. " ⁽²⁾

A wide spectrum of snails and semi- slugs (Gastropoda), including the African giant land snail, Achatina fulica, serve as intermediate hosts of the lungworm and it may occur also in a range of paratenic hosts. As a consequence, the route of infection in human cases varies geographically.
In Asia and Australia, most cases are probably acquired by ingesting raw intermediate hosts, snails, slugs or planarians either directly or on fresh vegetables that have not been thoroughly washed.
For example, by eating a small baby slug on a lettuce leaf.
According to University of Hawaii snail researcher Rob Cowie, it is when people touch or eat raw snails or slugs or their "slime trails" that the threat to human health occurs. ⁽⁴⁾
Slugs and snails can be clear and less than a centimetre long, making them hard to spot, but each one can carry thousands of worms.

The rat lungworm cycle.
    The rat lungworm. ⁽⁵⁾
Rats eating snails or slugs ingest "third stage" worms or parasites that penetrate through the intestine to the bloodstream. The parasites then reach the central nervous system of the rat, reaching the "fifth stage" or young adulthood. They mature in the bloodstream and mate in the rat's heart and pulmonary artery. The female parasite lays eggs that hatch into "first stage" worms that are expelled in the rat faeces and then eaten by slugs or snails.

The rat lungworm infection.
First reported case of human angiostrongyliasis ( rat lungworm infection ) acquired in Sydney in 2001.
A Sydney-based man ate two garden slugs Limax maximus, the leopard slug, an intermediate host for Angiostrongylus cantonensis as a dare during a party narrowly escaped death from a rare form of meningitis, an often fatal swelling around the brain.
As well as developing meningitis - inflammation of the membrane that surrounds the spine and the brain - the man developed encephalitis - swelling of the brain and spinal cord.

"He nearly died - his consciousness was impaired and he was very ill indeed in hospital. He had extremely high pressure inside his head,"
Dr.Pryor told ABC Science Online.
While the Sydney man survived, others have not been so lucky. In an earlier case, a young child in subtropical Brisbane died, believed to have eaten slugs crawling on milk bottles which had been left at the front door. Another man had acquired the disease during a holiday in Fiji.
However, the risk of dying from ingesting the parasites was "low".
One reason for the low risk is that the natural host for the parasite is the rat, and so if the parasite finds itself inside a human it tends to die off after a couple of weeks or so. "So you don't have to treat the disease - it cures itself when the organism dies, when it discovers you're not a rat."
"He had a lot of the organisms actually invade the brain," says Dr. Pryor of the Sydney man.
Source:  Man's brain infected by eating slugs - ABC Western Queensland - Australian Broadcasting Corporation  http://www.abc.net.au/science/articles/2003/10/20/969551.htm  Accessed: 22/12/2011
Source:  MJA 2003; 179 (8): 430-431   Accessed: 22/12/2011.

Symtoms and Human Eosinophilic Meningitis.
Angiostrongylus cantonensis, also known as Parastrongylus cantonensis, is the commonest infectious cause of eosinophilic meningitis worldwide.
Angiostrongylus meningitis is usually mild and resolves spontaneously over 6 weeks. Occasionally, cases are severe and may have chronic sequelae and death may incurr. ⁽⁶⁾
Severe Eosinophilic meningitis.
The immune reaction caused by the dead worms results in serious inflammation and damage in the nervous system and brain, and can lead to symptoms including headache, stiff neck, numbness, tingling or pain in the skin, fever, nausea and vomiting, blurred vision, weakness, joint pain and neurological abnormalities. More severe symptoms can include paralysis of the legs, bowel and bladder dysfunction, seizures, coma and, although rare, death. ⁽⁶⁾

How is it prevented?
Factsheet - NSW Health
• Don't eat raw snails or slugs. If eating snails, ensure they are thoroughly cooked first.
• Supervise infants and young children in environments where they may find snails and slugs.
• Wash fresh vegetables and lettuces well before eating in case they have snails or slugs (or their slime) on them.
• Wash your hands well after gardening or handling snails or slugs.
• Consider controlling snails and slugs around vegetable patches and gardens and control vermin around the home. If snail pellets or rodent baits are used it is very important that precautions are taken to ensure young children don't accidentally eat them.
 Source:  Factsheet - NSW Health http://www.health.nsw.gov.au/factsheets/infectious/rat_lung_worm.html

Other Articles at this site.
1:  Flesh-eating bacteria in Australia.
2:  Lethal ants in Australia.
3:  Chronology of Australian Major Bush fires.
4:  Chronology of Australian Major Droughts.
5:  Early Settlers' Homes and Bush Huts in Australia.
6:  Early Settlers in Victoria Australia.
7:  Is there a risk of a volcanic eruption in Australia ?

References and other Sources:
Source:⁽¹⁾ Image of slug Limax maximus and garden snail ( Helix aspersa ) courtesy of CSIRO, Gastropoda:
⁽²⁾ The spread of Angiostrongylus cantonensis in Australia. Southeast Asian J Trop Med Public Health. 2001;32 Suppl 2:126-8.  [PubMed - indexed for MEDLINE] http://www.ncbi.nlm.nih.gov/pubmed/12041575 
Accessed: 22/12/2013
Source:⁽³⁾  One Health Newsletter   Volume 4 Issue 1 Winter 2011  http://www.onehealthinitiative.com
Source:⁽⁴⁾ Robert H. Cowie  Pacific Biosciences Research Center, University of Hawaii, Honolulu, Hawaii Biology: taxonomy,identification, and life cycle of Angiostrongylus cantonensis.  
RAT LUNG WORM DISEASE SCIENTIFIC WORKSHOP HONOLULU, HAWAII AUGUST 16 - 18, 2011  
Accessed: 2/1/2013
Source:⁽⁵⁾ Image courtesy of ⁽⁴⁾ 
Source:⁽⁶⁾ Human angiostrongyliasis  Qiao-Ping Wang, De-Hua Lai, Xing-Quan Zhu, Xiao-Guang Chen, Zhao-Rong Lun www.thelancet.com/infection Vol 8 October 2008   Accessed: 22/12/2013

Further Reading:
• Gutteridge BH, Bhaibulaya M, Findlater C.  Human larval meningitis possibly following lettuce ingestion in Brisbane. Pathology 1972; 4: 63-64.
• Mason KV:  Haematological and cerebrospinal fluid findings in canine neural angiostrongylosis. Australian Veterinary Journal 66:152-154, 1989
• Prociv P, Carlisle MS. The spread of Angiostrongylus cantonensis in Australia.  Southeast Asian J Trop Med Public Health. 2001;32 Suppl 2:126-8.
• Sanjaya N Senanayake, Don S Pryor, John Walker and Pam Konecny  MJA 2003; 179 (8): 430-431
• Yang F:  Observation on the cats and a dog infected by Angiostrongylus cantonensis [Parastrongylus cantonensis]. Chinese Journal of Zoonoses 15, 1999