9. Heartworm disease. (symptoms, diagnosis, treatment and prevention)

Question 1

Heart worm disease info?

Answer 1

Technically a pulmonary disease; Adult worms are in the pulmonary arteries → RS of the heart is only involved later

Question 2

Parasitology of heartworm disease?

Answer 2

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

Question 3

Pathogenesis of heart worm disease?

Answer 3

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

Question 4

Clinical signs of heartworm disease?

Answer 4

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

Question 5

Diagnosis of heart worm disease?

Answer 5

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

Question 6

X- ray signs?

Answer 6

Question 7

Cat diagnosis?

Answer 7

Cat: History; CSx; Thoracic radiograph; Echocardiography;

Serology

Question 8

Treatment of heartworm disease?

Answer 8

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

Question 9

Treatment plan for dogs graph?

Answer 9

Question 10

Prevention of heartworm disease?

Answer 10

Prevention

Testing for AGs & microfilariae must be done before any

prophylactic treatment

Preventative treatment with macrocyclic lactones: Ivermectin;

Moxidectin; Milbemycin

Question 11

Prognosis of heartworm disease?

Answer 11

PROGNOSIS

Can be good → guarded, depending on severity

Caval syndrome: Poor → grave