Heart and Lung Worm

Question 1

Give an example of a heart worm, which species are hosts and intermediate hosts?

Answer 1

• Dirofilaria immitis
• Host - dog, cat
• IMH - mosquito

Question 2

Describe the distribution of D. immitis and the site that it affects in the host

Answer 2

• Distribution - US, warm temperate zones, tropics
• CVS - right atrium, posterior vena cava and pulmonary artery

Question 3

Describe the lifecycle of D. immitus

Answer 3

1. Adult worms in RV of heart
2. Adults release L1 (microfilaria) which enter systemic circulation
3. Microfilaria ingested by mosquito as it takes a blood meal
4. Microfilaria develop from L1 to L3 inside the mosquito in 10-14d
5. L3 transmitted to host via feeding of mosquito
6. L3 develop to L4 in the subcutaneous tissue
7. Juvenile adults migrate to the heart

Question 4

Describe the pathogenesis of D. immitus in the dog

Answer 4

• Low numbers of adult worms - little clinical effect
• High numbers of adult worms - clinically significant
• Chronic congestive right sided heart failure
• Pulmonary embolism - adults block pulmonary vessels
• Vena caval syndrome - becomes blocked with adults (acute condition)
• Endocarditis in valves, pulmonary endoarteritis (local inflammatory response)
• Glomerulonephritis (deposition of immune complexes)

Question 5

What are the clinical signs of heart wormn in the dog?

Answer 5

• Exercise intolerance
• Chronic soft cough
• CV dysfunction
• Gradual loss of condition

Question 6

How is heart worm diagnosed in dogs?

Answer 6

• Clinical signs and history
• Detection of microfilaria in blood
• Detection of circulating antigen (snap test) - detect females
• Some dogs have occult infections - adults but no MF

Question 7

What are the prophylactic measures associated with heart worm?

Answer 7

• Macrcyclic lactones monthly - kills L3
• Diethylcarbamazine daily

*both microfilaricidal - but don’t kill adults)

• Check MF status of dog
• Should really only treat MF -ve dogs (risk of anaphylactic shock)

Question 8

Describe the pathogenesis of D. immitus in cats

Answer 8

• Relates to inflammatory response rather than worm burden
• Are less susceptible
• Adult worm lives 2-3 yrs
• < 6 adult worms
• Lungs affected more
• Potentially fatal
• No approved treatment, usually allow spontaneous recovery

Question 9

Give an example of a lung worm in the dog, state it’s host, intermediate host adn site of action

Answer 9

• Angiostrongylus vasorum
• Host - dog, fox
• IMH - mollusc

Question 10

Describe the lifecycle of Angiostrongylus vasorum

Answer 10

1. Adults in heart
2. Female releases eggs which hatch in pulmonary capillaries
3. L1 break into alveoli and migrate through lungs, up trachea to pharynx
4. L1 are swallowed and excreted in faeces
5. L1 taken up by mollusc. Develop to L3 inside mollusc
6. L3 released into the environment by the mollusc
7. L3 ingested and develops to L4
8. Adults migrate to the R side of the heart

Question 11

Describe the pathogenesis of Angiostrongylus vasorum

Answer 11

• Pathology associated with adults in large vessels and eggs in pulmonary capillaries
• Chronic congestive heart failure
• Chronic infection
• Fibrosis of damaged arteries - ‘pipe stem’
• Lung mottled with penetrating L1

Question 12

What are the clinical signs of Angiostrongylus vasorum?

Answer 12

• Early on - asymptomatic
• Later - increased resp rate, cough on exercise
• Heavy worm burdern - fainting, sub cutaneous haematoma
• Can be associated with brain/spinal cord haemorrhage
• Parasite excretory products can interfere with blood clotting

Question 13

How is Angiostrongylus vasorum infection diagnosed and treated?

Answer 13

Diagnosis:

• Baermann on faecal sample
• PCR
• Ag test (IDEX)

Treatment:

• Panacur