Dirofilaria immitis

Jason Soderberg and Sam Rawson

Classification

Phylum: Nematoda Class: Secernentea Sub-class: Spiruria Order: Spirurida Family: Dirofilaria immitis

Geographical Distribution

World-wide but very common in mild to warm climates (where mosquitoes thrive)

Hosts

Definitive Host: Dogs, coyotes, wolves, cats Others that can be infected: humans,

beavers, and horses Intermediate Host:

Mosquito (Anopheles, Aedes, Mansonia and Culex spp)

Morphology

Adult: Females 230-310mm long by 0.35mm Male 120-190mm long by .300mm

Microfilariae 307-322µm by 6.8µm(no egg)

Larva 4 molts total

Life Cycle

Life Cycle

Mosquito introduces L3 filarial larvae into skin of DH

L3 molts into L4 and then again into adult form (in the subcutaneous tissue, takes 1-3

days) Adults reside in pulmonary arteries

and right ventricle of the heart Adults can live for 5-10 years

Life Cycle Continued

In the heart the female is capable of producing microfilariae (pre-larval stage)

Microfilariae are then pumped into the peripheral blood

Mosquito ingests microfilariae during blood meal

Microfilariae migrate to the mosquito’s midgut and develop into L1 and molt until L3

Human infection

In humans larvae generally move through the right ventricle to the lungs They often then lodge in small-caliber

vessels causing infarcts and typical “coin lesions” visible on radiographs

Forms a granuloma in lung and might resemble lung cancer on an x-ray (requiring biopsy)

Clinical Signs

Based on severity of infection, age of infection, and host’s immune response

Early stages- host may appear asymptomatic

Mild to moderate disease may include chronic cough, dyspnea, and exercise intolerance

Disease progression: congestive heart failure

Disease: Heartworm Disease Death may occur during cardiac hypertrophy

Due to microfilarial thrombi Pulmonary vessels may become thickened

and tortuous Cardiac output may be reduced Caval syndrome has been reported

Worms found in the post cava and right atrium causing interference of tricuspid valve ▪ leads to hemolytic anemia and right heart failure

Rarely systemic circulation or infection of the eye, CNS, or peritoneal cavity

Diagnosis

Blood tests: Antigen tests

ID of microfilariae on wet blood smear

ID of heart enlargement on radiographs

Treatment

Injections of melarsomine dihydrochloride into lumbar muscles 1 injection After 4 weeks, 2 more injections (24hrs apart)

Exercise must be limited for a month after each injection Decreases the chance of pulmonary

complications Prophylactic dose of Ivermectin will

eliminate microfilariae

Prevention

Test dog once a year for heartworms (blood test)

Heartgard preventative given once a month (contains ivermectin)

Review

What are the definitive and intermediate hosts?

Where is Dirofilaria immitis most commonly found?

How much damage can it cause in humans?

What disease does it cause?

Work Cited

http://www.vet.uga.edu/vpp/clerk/Lobeck/index.php

http://www.capcvet.org/capc-recommendations/canine-heartworm

http://bioweb.uwlax.edu/bio203/s2007/eddy_greg/habitat.htm