Filarioidea - dog/cat

Question 1

Name some general characteristics of the Superfamily Filarioidea.

Answer 1

• Tissue dwelling (i.e. do not inhabit in alimentary tract)
• Indirect LC - insect vectors as IMH
• More evolved spp release live L1 named microfilariae
• Dirofilaria immitis

Question 2

Name the host(s), IMH, site of infection, and distribution of Dirofilaria immitis.

Answer 2

• Host - dog mainly. Cat, ferret, sea lion, and possibly man.
• IMH - mosquito
• Site - Cardiovascular system. Right ventricle, posterior vena cava, pulmonary artery.
• Distribution - USA, warm temperate zones (Europe), tropics

Question 3

Describe the life cycle of Dirofilaria immitis.

Answer 3

• PPP 6 months
• Indirect life cycle
• Adults in heart release microfilaria (mf) into blood
• mf ingested by mosquitos where they develop from L1 to L3
• L3 transmitted to host when feeding
• L3-L4-adult after migrating to subcutaneous tissue
• juvinile adult migrates to heart

Question 4

What is the pathogenesis of Dirofilaria immitis?

Answer 4

• Depends on worm burden
  
  • Low numbers - possibly no apparent effects
  • High numbers - lot of problems (right-sided heart failure)
• Pathogenesis is associated with adults in heart
• Chronic congested right-sided heart failure (with ventricular hypertrophy)
• Pulmonary embolism (dying worms - consider when killing worms with drugs)
• Vena caval syndrome
• Endocarditis in valves
• Glomerulonephritis (deposition of immune complexes in kidney)

Question 5

What are some clinical signs of Dirofilaria immitis infection?

Answer 5

• CV dysfunction
• Listless, or gradual loss of function
• Exercise intolerance
• Chronic soft cough

Question 6

How is Dirofilaria diagnosed?

Answer 6

• Detection of microfilaria in blood
• Detection of circulating antigen (SNAP test)
• Clinical signs and history

Question 7

Do antigen tests detect males or females?

When should testing start?

Does a negative microfilaria test mean the patient is Dirofilaria immitis free?

Answer 7

• Only females. They’re very sensitive and can detect the presence of one adult female.
• 6-7 months of age (PPP - 6 months)
• No. The patient can have an occult infection - adults, but no microfilaria.

Question 8

What are some factors affecting the epidemiology of Dirofilaria immitis?

Answer 8

• Dog
  
  • density of dogs
  • mf present for long periods in the dog (up to 5 years)
  • poor immune response to infection
  • poor owner compliance in giving HW meds
• Mosquito
  
  • distribution of susceptible vectors
  • capacity for rapid population increase
  • short developmental period (mf to L3)

Question 9

What are some methods of controlling Dirofilaria immitis spread?

Answer 9

• Prophylactically treat pets - macrocyclic lactones, for example, monthly
• However, these prophylactic drugs don’t kill adults
• Keep animals indoors at peak mosquito times (dusk)
• Insecticide collars/spot-ons
• Try to reduce mosquito populations
• Prophylaxis
  
  • check mf status (ideally it should be negative)
  • if positive, treatment could induce anaphylactic shock due to microfilaricidal actions of ivermectin (a type of mac lactone)

Question 10

What are some methods of treating HW+ dogs?

Answer 10

• Surgical removal of worms
• Melarsomine (Immidicide) treatment
• Treat to kill mf and wait til adults die
• Kill Wolbachia (bacterial endosymbiont) with doxy, and treat with ivermectin at the same time