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| Dirofilaria Immitis- heartworm |
- Large worms.
- Either produce larvated eggs or the L1 (first larval stage) are born live. (L1-L5 stages generally, L5= adult stage).
- Invertebrate intermediate host.
Dirofilaria Immitis 'heartworm' - Viviparous- gives birth to live L1 which are known as microfilarie.
- Found in the dog and cat and can grow as big as 30cm.
- The 'french heartworm' in comparison (Angiostrongylus Vasorum) is only 2.5cm.
- Transmitted by mosquitoes. Aedes and culex species.
- Rarely zoonotis (dirofilariasis).
Life Cycle
- Infected dog is bitten by mosquito.
- L1 microfilarie in mosquito vector.
- Moult-> L3 in mosquito head taking 12-14 days at 27 degrees. L3 is the infective stage.
- Susceptible dog bitten.
- Moults to L4 stage which takes 3-4 days and migrates to the abdomen.
- Moults to L5 (adult) stage which takes 2 months and then penetrates the jugular vein.
- Adults reside in the pulmonary arteries and into the right ventricle of the heart if there is heavy infection.
- Microfilarie appear in the blood of the dog 6-9 months after infection.
Clinical Signs
Cats & Ferrets-> generally possess lower worm burdens of only one to three adult worms. The worms are stunted and there is only transient microfilarie. In cats clinical signs vary from digestive/neurological signs to pulmonary symptoms, although signs may be moderate. Sudden death in cats is more common than in dogs.
Dogs-> Chronic disease which often presents as exercise intolerance. Cough, dyspnoea and lipothymia. Anorexia, and right sided heart failure. Death follows respiratory distress (blockage of the pulmonary artery) or cachexia. Small dogs develop acute 'caval syndrome,' intravascular haemolysis and haemoglobinuria. These dogs require immediate surgery.
Diagnosis
- Knott test/blood filtration to detect microfilarie. However 30% of fogs and most cats are amicrofilaraemic so won't show microfilarie in the blood when infected.
- Immunoassays for adult worm antigen (needs female worms present). Also for antibodies.
- Radiography and echocardiography.
Dirofilaria Repens
- Zoonotic dirofilariasis.
- Benign subcutaneous nodular swellings.
- Larger than immitis with an umberella handle tail and stains with acid phosophatase.
Prophylaxis and Treatment
Monthly prophylaxis with macrolactones such as ivermectin. This prevents larval development but will not kill the existing adult worms.
Macrofilarie treatment carries a risk of thromboembolism so the worm burden should be assessed before treatment. Treat with melarsomine and restrict exercise for 30-40 days after treatment. Doxycyclin and ivermectin has been found to have good efficacy in trials.
- Model for human onchocerciasis.
Superfamily- spiruroidea
Thelazia
T.Callipaeda-> dogs and cats. Parasitise the eyelids, tear glands and tear ducts. Transmitted by non-biting fruit flies e.g. phortica.
- Horses.
- Reside in stomach. Eggs in the faeces.
- Larvated eggs consumed by the maggots of musca and stomoxy flies.
- Infective larvae depositied on the moist surface of the lip, eye and on wounds.
- Disease-> larvae in open sores & on the conjunctiva.
Parafilaria
P.multipapillosa
- Horse.
- Haemorrhagic subcutaneous nodules.
- 'Summer bleeding.'
- Transmitted by haematobia.
P.bovicola
- Cattle.
- Verminous Haemorrhagic Dermatitis.
- Transmitted by Musca flies.
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