9. Heartworm disease. (symptoms, diagnosis, treatment and prevention) Flashcards
Heart worm disease info?
Technically a pulmonary disease; Adult worms are in the pulmonary arteries → RS of the heart is only involved later
Parasitology of heartworm disease?
PARASITOLOGY
Dirofilaria immitis – Transferred by mosquitos
Definitive host & main reservoir: Dogs & wild canids (cats
occasionally infected)
HARD (Heartworm Associated Respiratory Disease): No
maturation, but migration of larvae within the lungs
Severity of infection is dependent on: No. of worms; How long they have been present; Body’s reaction to the infection; Exercise of the animal; Size of the animal
Pathogenesis of heart worm disease?
PATHOGENESIS
Live adult worms
→ Mechanical trauma; Immunosuppressive effect
→ Damage the intima of blood vessels → Vascular lesions
Dead adult worms
→ More severe vascular reactions → Lung pathology
→ Thrombi → Embolisation, inflammation & fibrosis
Inflammatory mediators from heart worm → Hypoxia →
Vasoconstriction → Bronchoconstriction → Parenchymal lung inflammation & mild non-cardiogenic oedema formation
Pulmonary artery disease → Interstitial fibrosis
Thromboembolism after treatment with adulticide medication
§ Worm accumulation → Tricuspid regurgitation
§ Long-term infection → Caval syndrome (see later) →
CHF
Other consequences: Liver damage; Cirrhosis; Glomerulonephritis
Clinical signs of heartworm disease?
CLINICAL SIGNS
Mild form: Ø CSx; Chronic cough
Moderate form: Cough; Exercise intolerance; Abnormal lung sound
Severe form: Cough; Epistaxis; Exercise intolerance; Dyspnoea;
Abnormal heart & lung sounds; Hepatomegaly; Syncope; Ascites
Caval syndrome
Adult worms are displaced from the pulmonary arteries to the right
side of the heart; Seen more so in small dogs
§ Sudden: Lethargy; Weakness; Haemoglobinuria
§ CSx associated with RS-CHF
§ Tricuspid cardiac murmur
Cat: Bronchitis; Asthma signs; Intermittent vomiting; Lethargy;
Cough; Dyspnoea
Death of adult worm → HARD & shock → Death
Diagnosis of heart worm disease?
DIAGNOSIS
Serologic (Antigen) testing: Recommended for routine screening
Note: This only detects adult female worms; May produce falsenegative results in cats
“Drip test”; Modified Knott test; PCR
Bloods: Eosinophilia; Basophilia; Neutrophilia; Monocytosis
Echocardiography:
§ RA/RV dilation
§ RV hypertrophy
§ Paradoxical septal motion
§ Small left heart
§ Pulmonary artery dilation
ECG: Usually normal
Radiology
Used to support diagnosis
§ Pulmonary hypertension
§ RV enlargement
§ Enlarged pulmonary arteries
Thromboembolism signs
X- ray signs?
Cat diagnosis?
Cat: History; CSx; Thoracic radiograph; Echocardiography;
Serology
Treatment of heartworm disease?
TREATMENT
Asymptomatic/Mild disease: Ø
Moderate-severe/Concurrent: Challenging to treat
Goals: Improve clinical condition of the animal; Eliminate all life stages of HW
Adult HW tx: Melarsomine
Microfilariae HW tx: Moxidectin; Imidaclopride (macrocyclic lactones)
High-risk dogs: Stabilise before Melarsomine treatment
Dogs with RS-HF: Furosemide; ACE-inhibitor; Inodilator
Treatment plan for dogs graph?
Prevention of heartworm disease?
Prevention
Testing for AGs & microfilariae must be done before any
prophylactic treatment
Preventative treatment with macrocyclic lactones: Ivermectin;
Moxidectin; Milbemycin
Prognosis of heartworm disease?
PROGNOSIS
Can be good → guarded, depending on severity
Caval syndrome: Poor → grave