Dirofilaria Immitis
Heartworm Disease
Dirofilaria Immitis
Heartworm Disease
• Parasitic disease affecting dogs, cats,
foxes, wolves, muskrats and rarely man.
• Mosquito is the vector
• Worldwide range wherever dogs and
mosquitoes are prevalent and
temperatures are warm enough to support
growth within the mosquito vector
• Potential Zoonotic disease (lung nodules
in humans bitten by infected mosquito
Dirofilaria immitis
Adult Heartworms
Heartworm Disease
Microfilaria
Heartworm Disease
Life Cycle Dog
• Transmitted by over 60 species of mosquitoes.
• Adult heartworms reside in the pulmonary arteries or
right ventricle and produce microfilaria.
• The microfilaria are ingested by feeding mosquitoes and
the heartworm larvae undergo molts (2 weeks) to
become infective to dogs.
• The infective larvae are transmitted back to the dog
during feeding.
• The larvae initially stay in the subcutaneous tissue
mature and enter the vascular system and migrate to the
heart and lungs where final maturation occur.
Completion of life cycle usually takes 6-7 months
Heartworm Disease Life Cycle
Cats
• Similar but longer life cycle. The prepatent
period is approximately 8 months.
• Less than 20% of the infected cats develop
microfilaria
• Cats are deemed an unnatural host and are
inherently resistant to infection. Infections tend
to be infrequent and small. Low worm loads
make conventional antigen tests inaccurate
• In experimentally infected cats less than 25% of
the larvae reach adulthood
Heartworm Disease
Lifecycle
Heartworm Disease
Pathology
• The main area of pathology is the
pulmonary artery.
– Thickening, diminished diameter, inflammation
of the pulmonary artery. Secondary
pulmonary hypertension.
– Right side heart failure with ascites
– Thromboembolism due to dead worms
– The pulmonary arterial response in cats is
also very severe even with low worm loads
Heartworm Disease
Pathology
Large worm load in both
The pulmonary artery and
Right heart
Heartworm Disease
Primary pathology is in the pulmonary
Artery and Lungs
Pulmonary artery inflamation, fibrosis
With pulmonary hypertension
Thromboembolism due to dead adult
worms
Heartworm Disease
Symptoms Dogs
• Low worm loads are asymptomatic
• Weight Loss
• Chronic Cough
• Exercise Intolerence
• Syncopy (feinting)
• Ascites (abdominal distention)
Heartworm Disease Symptoms
Cats
• Most cats show respiratory signs
– 1. Dyspnea**
– 2. Cough**
– 3. Vomiting
– 4. Collapse
– 5. Sudden death
Heartworm Disease
Diagnosis Dogs
• Microfilaria Detection
– Modified Knotts Test
– Direct Blood Smear—Dipetalonema
reconditum (Acanthocheilonema) a differential
– Larvae are more active at night and during the
summer months. Amicrofilaremic infections
(10-20%), single sex infections (male), and
drug induced microfilaria death make these
test less sensitive
Heartworm Disease
Immunodiagnostic Tests Dogs
• Commercial Antigen Tests
• Good Sensitivity and Specificity
– The weakness of these tests is that they
detect antigen from female adult heartworms.
– The tests will be negative for the first 5-8
months of infection. Male infections will be
negative and low worm burdens may not test
positive.
Heartworm Disease
Diagnosis Dogs
• Radiology
– Radiographic abnormalities, which develop
early in the disease, are present in 85% of the
cases.
Heartworm Disease Diagnosis
Cats and Ferrets
• Cats have a low worm burden and often do
not have microfilaria
• Feline patients—antibody test to determine
exposure
• Commercial Antigen Tests
• Feline patients and Ferrets- Ultrasound
(Echocardiography) can help diagnose the
disease
• Radiology
Heartworm Disease
Treatment Dogs
• Melarsomine (Immiticide) Adulticide
• an organoarsenic. Given two doses 24
hours apart
• Ivermectin (microfilaria) Can be given at
a high dose once or given by monthly
preventative doses
Heartworm Treatment
Cats
• +/- Adulticide treatment (arsenicals)
• Corticosteroids
• Oxygen
• Bronchodilators
• +/- Aspirin
Heartworm Disease
Prevention Cats
• Necropsy studies of feline Heartworm
Infection in the southeastern part of the
US average 7% (close to the rate of FELV)
• 1998 a nationwide antibody survey of
2000 cats revealed and antibody exposure
rate of approximately 12%
Heartworm Prevention
Dogs
