Tropical Angiostrongylus

Question 1

What superfamily do Angiostrongylus spp. belong to?

Answer 1

Metastrongyloidea - bursate nematodes

Question 2

Which species are important and where are they important?

Answer 2

A. cantonensis and costaricensis are important in warmer climates

A. vasorum is important worldwide.

Question 3

What is A. cantonensis commonly known as?

Answer 3

The rat lungworm - as it resides in the pulmonary arteries of rats.

Question 4

What are the hosts of A cantonensis?

Answer 4

Rat final host
Molluscan intermediate host
Humans & crustaceans can act as paratenic hosts

Question 5

Where is A. cantonesis distributed?

Answer 5

Tropical/sub-tropical regions, S.E asia, australia, india, africa….

Question 6

How can the female cantonensis worm be distinguished from the male worm and why is this?

Answer 6

Barber’s pole appearance, blood and white uterus.

Question 7

Describe the life cycle of A. cantonensis.

Answer 7

L3 larvae in molluscs ingested by rats. The L3 then migrates via the hepatic portal system to the lungs and circulation of the CNS. Moulting through L4 to L5 occurs within a few hours and the L5 migrates to the pulmonary artery via the cerebral vein where they mature to adults and mate. Thin shelled eggs get to the alveolar capilaries where they hatch into L1 larvae which enter the alveoli and are coughed up and swallowed. L1 are excreted in the faeces and will penetrate a mollusc to develop to L3 in 2 weeks. The PPP in the rat is 6 weeks

Question 8

When is A. cantonensis at its highest?

Answer 8

In rainy weather

Question 9

How can humans become infected with A.cantonensis?

Answer 9

Eating raw/undercooked molluscs or crabs/prawns.

Eating unwashed vegetables (as they may have slime containing L3)

Question 10

What is the main pathology of A.cantonensis in rats and in humans?

Answer 10

Rats - heammorhages of alveolar capillaries
- granulomas, haemorrhages and abscesses in the brain

Humans - eosinophilic meningitis/meningo-encephalitis which is highly fatal

Question 11

What clinical signs are noted in rats infected with A.cantonensis?

Answer 11

Ranges from asymptomatic light infections to incoordination, bloody nasal and ocular discharge and coughing and sneezing in heavy infections.

Question 12

What are the clinical signs seen in humans infected with A.cantonensis and when do they occur?

Answer 12

1-3 weeks p.i. - stiff neck, headaches, visual disturbance, pins and needles (paraethesia), nausea, vomiting, fever, coma and death in severe cases (2-3%)

Question 13

How is A. cantonensis visualised in rats?

Answer 13

Baerman technique - see L1 under microscope.

Question 14

How is A. cantonensis diagnosed in humans?

Answer 14

CASE HISTORY!
Imaging and clinical examination (eye)
CSF - worms (rare)
Serology

Question 15

What are the difficulties in treating human A. cantonensis infection?

Answer 15

Anthelimintic treatment killing worms could lead to an inflammatory response in the CNS.

Surgery or laser treatment can be used as well as supportive treatment e.g. lumbar puncture and anti inflammatories.

Question 16

Outline the principles of control of A. cantonensis in humans.

Answer 16

Education so people properly wash and cook foods (salad, crustaceans and molluscs)

Vector control is not practical.

Question 17

How does the epidemiology of A. costaricensis differ to that of A. cantonensis?

Answer 17

Rats AND humans can act as a FINAL host. Slugs and snails act as intermediate hosts.

Question 18

Where does A. costaricensis occur?

Answer 18

Central (endemic) and south (sporadic) America

Question 19

Outline the LC of A. costaricensis.

Answer 19

L3 migrate and moult through the lymphatics to the ileo-caecal arteries where they mature to adult worms. Eggs pass into the intestinal wall where they hatch. L1 larvae burrow through the intestinal wall into the lumen and pass out in the faeces. This takes 3-4 weeks.

Question 20

What is the main definitive host of A. costaricensis.

Answer 20

The cotton rat

Question 21

What is the pathology of A. costaricensis in rats and humans?

Answer 21

Adult worms cause haemorrhage (rats) and eosinophilic granuloma formation leading to mucosal thickening (humans). Large numbers of eggs in rats can cause a yellowing of the serosal surface.

Question 22

What are the clinical signs of A. costaricensis in

a) rats
b) humans

Answer 22

a) Heavy infections can lead to vascular obstructions and infarcts of the gut wall and death.
b) Abdominal pain, annorexia, vomiting, diarrhoea and fever

Question 23

How does diagnosis differ to that of A.cantonensis?

Answer 23

Can also PM rats and see the necrosis or adult worms in ileo-caecal arteries.

Humans - can palpate abdominal mass, biopsies would reveal eggs, larvae in blood vessels and tissue eosinophilia.

Question 24

Does treatment differ much to that of A. cantonensis?

Answer 24

No, maybe more surgery though?