HEARTWORM DISEASE

• PREVALANCE

• LIFE CYCLE

• DIAGNOSIS

• TREATMENT

TINY• 3 yr old MN Rottweiler

• Treated for heartworm disease last year with Immiticide

• Has had repeated ELISA Ag test negative since then

• How is he now Heartworm Positive?

Origin

• Dirofilaria immitis: first originated in Asia then spread to the Mediterranean countries.

• Brought to the Americas from early explorers and immigrants with their dogs

• Was first reported in the US in a dog from Erie, Alabama

PREVALANCE

From Bowman DD, Susan EL, Lorentzen L, et al. Prevalenceand geographic distribution of Dirofilaria immitis, Borrelia burgdorferi, Ehrlichia canis, and Anaplasma phagocytophilum in dogs in the United States: Results of a national clinic-based serologic survey. Vet Parasitol 2009;160(1/2):138–48

Transmission

• Most common in late summer– July-August

• Reservoir host: domesticated and wild canids• Intermediate hosts: Mosquitos• Felines: tend not to be biologic hosts – Can still become infected

• Other mammals, including humans can acquire nonpatent infections

LIFE CYCLE

LARVAL MIGRATION

Kotani T, Powers KG. Developmental stages of Dirofilaria immitis in the dog. Am J Vet Res1982;43(12):2199–206

DIAGNOSIS

• ANTIGEN TEST: Will detect the presence of adult female worms at least 6 months old

• Microfilaria test: can be present 6 months post-infection but typically by 7-9 months– Less sensitive; especially if on a macrocyclic lactone– Helps to identify patient as a reservoir

• For cats; difficult to detect. If clinical suspicion recommend both antigen and microfilaria test

Diagnosis

• Thoracic Radiographs: Can help evaluate severity of disease

• CBC

• Serum Chemistry: Hemoglobinemia can be seen with caval syndrome

• Urinalysis: Hemoglobinuria can be seen with caval syndrome

Thoracic Radiographs

• Parenchymal PA enlargement, truncation, and/or tortuosity – pulmonary hypertension and/or loss in laminar

blood flow• Peripheral focal or multifocal alveolar

pulmonary pattern – PTE caused by dead adult worm fragments or

secondary eosinophilic pneumonitis

Textbook of Veterinary Diagnositc Radiology, 5th edition. Thrall. 2007, p 583-4

Thoracic Radiographs

• MPA dilation– caused by turbulent blood flow and pulmonary

hypertension and possibly the presence of heartworms

• RV hypertrophy– in response to pulmonary hypertension

• Hepatomegaly, ascites, and occasionally pleural effusion– caused by right-sided heart failure

Textbook of Veterinary Diagnositc Radiology, 5th edition. Thrall. 2007, p 583-4

FELINEFOCAL PATCHY ALVEOLAR PATTERN

L. Venco, Clinical evolution and radiographic findings of felineheartworm infection in asymptomatic cats. Veterinary Parasitology 158 (2008) 232–237

Focal Caudodorsal Oligemiasuggestive of thromboembolism

L. Venco, Clinical evolution and radiographic findings of felineheartworm infection in asymptomatic cats. Veterinary Parasitology 158 (2008) 232–237

Angel: 6yr FS DSH

Right caudal pulmonary artery enlargement

Tiny: 3yr MI Rottie

MPA enlargement, tortuous enlarged pulmonary arteries with normal veinsDiffuse bronchointerstitial pattern

Tiny: Left Lateral

Previously treated for HW 1 year ago; unknown protocol

• Live heartworms: – can cause endarteritis and muscular hypertrophy of

arteriole walls especially in the caudal pulmonary arteries

• Dying/dead HWs: – decompose and small worm fragments lodge in

distal pulmonary arteriole and capillary beds in the caudal lung lobes. Worm fragments with inflammation and platelet aggregation results in PTEs

TREATMENT

• An adult heartworm can live up to 7.5 years• Microfiliaria can live up to 2.5 years in the

blood• Need proper treatment protocols to

eradicate both the larval, juvenile, and adult heartworms

TREATMENT

• Adulticide:Melarsomine(Immiticide)– No activity against worms less than 4 months old

• Larvacide: Macrocyclic lactones– Work against microfilaria, L3, L4 and some young adult

heartworms. Does not work well against later 4th stage and juvenile worms

• Doxycycline: Endosymbiont of D. immitis is a Rickettsial infection of Walbachia– As kill heartworms they can release the Walbachia

• Treating with doxy may help decrease lung pathology

Feline Treatment

• Treatment of Choice:– Surgical removal of worms

• If not clinical may be prudent to not tx– Give prednisone to prevent secondary

inflammation• Immiticide: Not recommended and may be

toxic

TREATMENT GAPS

Image from: www.americanheartwormsociety.org, Heartworm Infection in Dogs

Treatment

• To help with the treatment gap– Treat with 2-3 months of macrocylic lactone first– eliminate the migrating larva less than 2 months

old and allow those worms between 2 and 4 months of age to reach an age at which they are susceptible to immiticide.

• Then give injection of immiticide• 1 month later give second injection• 24 hours later give 3rd injection

TREATMENT OF CAVAL SYNDROME

• Adult heartworms partially obstruct blood flow through the tricuspid valve and interferes with closure– Can then cause passive congestion of the liver. – CS: sudden onset of lethargy, weakness, with

hemoglobinemia and hemoglobinuria. – See on echo: HWs within the tricuspid orifice and

caudal vena cava.

Caval Syndrome Treatment

• If treat with an adulticide– Die off will be numerous and rapid– Likely will lead to pulmonary emboli and severe

inflammatioin– Increased morbidity and mortality

• Need to decrease worm burden surgically first

SURGICAL RETRIEVAL

• Via right jugular vein: pass a flexible alligator forceps or an intravascular retrieval snare under fluoroscopic guidance

Image from: www.americanheartwormsociety.org, Heartworm Infection in Dogs

Caval Syndrome Treatment

• After surgical removal of worms– Murmur should resolve– Hemoglobinuria and hemoglobinemia should

resolve in 12-24 hours

– In a few weeks can continue with normal treatment protocol