PARASITOLOGY - Heartworm Flashcards
Which nematode is the most common cause of heartworm in dogs?
Dirofilaria Immitis
What type of lifecycle does dirofilaria immitis have?
Indirect lifecycle
What is the most susceptible final host to dirofilaria immitis?
Dogs
What is the intermediate host of dirofilaria immitis?
Mosquito
What is the infective stage of the dirofilaria immitis lifecycle?
L3 larvae
Describe the lifecycle of dirofilaria immitis
- Mosquito ingests microfilaria during a blood meal
- Microfilaria develop into L3 larvae within the mosquito
- Mosquitos feed on another blood meal and transmit the L3 larvae into the bloodstream of the final host
- L3 develop into L4 larvae within the subcutaneous tissue
- L4 larvae migrate through the tissues where they develop into juveniles
- Juveniles migrate to the right side of the heart and develop into adults
- Adult dirofilaria immitis produce microfilaria which will be released into the bloodstream
What is the optimal temperature required for the development of dirofilaria immitis microfilaria into L3 larvae in the mosquito?
18°C
What is the pre-patent period (PPP) of dirofilaria immitis?
Six months
(T/F) The pathogenesis of dirofilaria immitis is dependent on the number of dirofilaria immitis adult worms
TRUE.
What are the five possible consequences of a heavy dirofilaria immitis infection?
Right-sided congestive heart failure
Pulmonary arterial thrombosis
Vena caval syndrome
Endocarditis
Glomerulonephritis
What is vena caval syndrome?
Vena cava syndrome is the partial or complete blockage of the vena cavae
How does a heavy dirofilaria immitis infection cause glomerulonephritis?
Female dirofilaria immitis adult worms produce antigens, stimulating the host immune system to form antigen-antibody complexes which can be deposited into the glomerulus, causing glomerulonephritis
What are the four clinical signs of a dirofilaria immitis infection?
Exercise intolerance
Gradual loss of body condition
Chronic soft cough
Cardiovascular dysfunction
What are the six methods which can be used to diagnose dirofilaria immitis?
Assess clinical signs
History
Radiography
Echocardiography
Detection of microfilariae in the blood
ELISA
What can lead to a false negative when detecting dirofilaria immitis microfilariae in the blood?
Dogs can have a occult infection where they have adult dirofilaria immitis worms but there are no microfilariae in the blood
What can lead to a false negative when carrying out an ELISA for dirofilaria immitis?
ELISA cannot detect male adult worms as only the female adult worms produce antigens
Where is dirofilaria immitis endemic?
United States of America (USA)
Southern Europe
When are dirofilaria immitis infections seen in the UK?
Dirofilaria immitis infections are only seen in imported dogs in the UK
What is the best way to control dirofilaria immitis?
Prophylactic drugs
When should prophylactic drugs be given to animals living in tropical climates to control dirofilaria immitis?
In tropical climates, prophylactics should be given to animals all year round to control dirofilaria immitis
When should prophylactic drugs be given to animals living in warm, temperate climates to control dirofilaria immitis?
In warm temperate climates, prophylactics should be given two months before, during and two months after mosquito season
Which anthelmintic drug classification is most commonly used as prophylaxis for dirofilaria immitis?
Macrocyclic lactones
Give an example of a macrocyclic lactone commonly used as prophylaxis for dirofilaria immitis
Moxidectin
Which stage of the dirofilaria immitis lifecycle is targeted by macrocyclic lactones?
L3 and L4 larvae
Why is it so important to check for the presence of dirofilaria immitis microfilariae in the blood before administering prophylactic drugs?
If there is a heavy dirofilaria immitis infection, there can be an overwhelming release of antigens by the microfilariae following the administration of a prophylactic drug which can lead to anaphylactic shock
Which drug should be used to treat a dirofilaria immitis infection if the animal is at risk of anaphylactic shock?
Topical moxidectin as this limits the risk of anaphylactic shock
Give an example of an anthelmintic drug which can be used to kill adult dirofilaria immitis worms
Diethylcarbmazine (DEC)
Why is moxidectin often given in combination with the antibiotic doxycycline to treat dirofilaria immitis?
Doxycycline will target the Wolbachia bacteria which live within adult female dirofilaria nematodes. Killing the Wolbachia sterilises the females resulting in eventual death
(T/F) Dirofilaria immitis is not pathogenic in cats
FALSE. Dirofilaria immitis is very pathogenic in cats as only a small worm burden is required to cause disease
What causes the pathology of a dirofilaria immitis infection in cats?
Unlike dogs, the pathology of a dirofilaria immitis infection in cats is not caused by the worm burden but instead the inflammatory response to the antigens produced by the female adults and microfilariae
What type of lifecycle does angiostrongylus vasorum have?
Indirect lifecycle
What is the final host of angiostrongylus vasorum?
Dogs
What is the intermediate host of angiostrongylus vasorum?
Molluscs
Describe the lifecycle of angiostrongylus vasorum
- Molluscs infected with L3 larvae are ingested by the host
- L3 larvae penetrate the intestinal mucosa and enter the bloodstream where they will eventually develop into adults
- Adults migrate to the right side of the heart
- Adults lay eggs in the pulmonary capillaries
- Eggs hatch into L1 larvae in the pulmonary capillaries
- The L1 larvae will migrate through the pulmonary capillaries into the alveoli and through the lungs to the trachea where they will be coughed up and swallowed
- L1 larvae are excreted in the faeces
- Molluscs ingest the L1 larvae whilst feeding on the host faeces
- L1 larvae develop into L3 larvae within the mollusc
What are the three consequences of an angiostrongylus vasorum infection
Right-sided congestive heart failure
Blood vessel fibrosis
Increased coagulation time
How does a angiostrongylus vasorum infection increase coagulation time?
Angiostrongylus vasorum adults secrete products which interfere with coagulation and thus increase coagulation time
What are the five main clinical signs of an angiostrongylus vasorum infection?
Exercise intolerance
Increased respiratory rate
Coughing
Haematomas
Cardiovascular dysfunction
What are the three methods that can be used to diagnose an angiostrongylus vasorum infection?
Identify L1 larvae in the faeces
PCR
Antigen test (IDEX test)
Which technique should be used to identify L1 angiostrongylus vasorum larvae in a faecal sample?
Baermann technique
