Dirofilaria immitis Kristi Bjerke & Heather Lee. Taxonomy CLASS: SECERNENTEA SUBCLASS: SPIRURIA –ORDER: SPIRURIDA SUPERFAMILY: FILARIOIDEA –FAMILY: ONCHOCERCIDAE.

Dirofilaria immitis

Kristi Bjerke&

Heather Lee

Taxonomy

CLASS: SECERNENTEA• SUBCLASS: SPIRURIA

– ORDER: SPIRURIDA•SUPERFAMILY: FILARIOIDEA

– FAMILY: ONCHOCERCIDAE » Scientific name - Dirofilaria immitis» Common name - Dog heartworm

Hosts

• Definitive Host: dogs, foxes, wolves, coyotes, cats, ferrets, sea lions

• Intermediate Host: Over 70 species of mosquitoes

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Geographic Distribution

• Worldwide– Most common in mild and warm

climates





Morphology• Adults are long,

white, thread-like worms– Females 25 to

30cm long– Males 12 to 16

cm long with spirally coiled tail

Morphology

• give live birth and the baby worms are called Microfilariae

• Microfilariae– Sheathless– 218 to 329µm long – have a long pointed tail

Life Cycle



Life Cycle• A dog infected by microfilariae is bitten

by a mosquito• If the microfilariae is not picked up by a

mosquito after 2 years, they die of “old age.”





•Microfilariae can be transmitted across the placenta.•Puppies will not develop adult heartworms because the microfilariae didn’t go through the intermediate







Life Cycle• Inside the mosquito, the

microfilariae develop to L2’s and finally to L3’s.

• The L3 is the infective stage for dogs.– Takes a few weeks– Temperature dependant

• Minimum of 57 ºF is required

Life Cycle

• The L3 is deposited in mosquito saliva next to the bite and then migrate into the body.

• The average mosquito can only transmit a maximum of 10 infective larvae at one time

• The L3 larvae then live in the dogs skin where they develop into an L4 stage.

• They then live in the subcutaneous tissues and muscle for 3 months before they finally molt into an adult.





Life Cycle• Adults migrate to the right side of

the heart and into the pulmonary arteries and lungs where they mate and produce microfilariae.





–The overall maturation and migration process until mating takes approximately 5-7 months–Adult worms can live in the dog for up to 5 years

Pathogenesis of the Heart• Heavy infections(over 25

worms for a 40 lb dog)– worms begin to back up

into the right ventricle • less blood pumped.

• Over 50 worms the ventricle is full and the atrium begins to contain worms.

• Over 100 worms the entire right side of the heart is filled – phenomenon is called

"Caval Syndrome" and most dogs do not survive it.





Canine Symptoms• Cough, exercise intolerance• dyspnea (difficulty breathing)• abnormal lung sounds• hepatomegaly (enlargement of the

liver)• syncope (temporary loss of

consciousness due to poor blood flow to the brain)

• ascites (fluid accumulation in the abdominal cavity)

• abnormal heart sounds• death





Feline Symptoms• Non-specific generic signs of illness

– Vomiting intermittently– Lethargy– Lack of appetite– Weight loss– Coughing– Asthma-like signs– Gagging– Difficult or rapid breathing

• The early signs (when worms are carried to the pulmonary arteries) are often misdiagnosed as asthma or allergic bronchitis– Actually Heartworm Associated Respiratory Disease

(HARD)





Heartworm in Cats vs. Dogs









Diagnosis

• Blood Tests– Filter test to look for microfilariae

• Doesn’t work well for small infections

– Antigen test screens for pieces of adult heartworm skin in the blood

• Only works for female worms• Need at least 3 for it to be detected

– Newer tests test for antibodies

• X-rays– Enlargement of lobes of lungs or right side

of heart





Treatment

• Adulticide– Melarsomine dihydrochloride

(Immiticide®)• Intramuscular injection into lumbar muscles• Complications include thrombosis (clogging) of

pulmonary arteries due to dead worms

– No current treatment for cats

• Microfilaricide– macrocyclic lactone (ML) anthelminthics,

i.e.,milbemycin oxime, selamectin, moxidectin and ivermectin

– Commonly used in heartworm preventative





Control/Prevention• Can be given as

– Monthly Tablets– Chewables– Topicals

• Ivermectin– Heartgard, Heartgard Plus, Tri-Heart, Iverheart Plus

• Milbemycin oxime– Interceptor, Sentinel

• Selamectin– Revolution

• Moxidectin– Advantage Multi









http://www.heartwormsociety.org/quiz.asp




Dirofilaria immitis Kristi Bjerke & Heather Lee. Taxonomy CLASS: SECERNENTEA SUBCLASS: SPIRURIA –ORDER: SPIRURIDA SUPERFAMILY: FILARIOIDEA –FAMILY: ONCHOCERCIDAE.

Documents

intermediate slide

dog heartworm slide

life cycle slide

dog worms

coiled tail slide

warm climates slide

long pointed tail slide

baby worms