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Dirofilaria immitis

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.

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Dirofilaria immitis

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  1. Dirofilaria immitis Kristi Bjerke & Heather Lee

  2. Taxonomy CLASS: SECERNENTEA • SUBCLASS: SPIRURIA • ORDER: SPIRURIDA • SUPERFAMILY: FILARIOIDEA • FAMILY: ONCHOCERCIDAE 
 • Scientific name - Dirofilaria immitis • 
Common name - Dog heartworm

  3. Hosts • Definitive Host: dogs, foxes, wolves, coyotes, cats, ferrets, sea lions • Intermediate Host: Over 70 species of mosquitoes

  4. Geographic Distribution • Worldwide • Most common in mild and warm climates

  5. Morphology • Adults are long, white, thread-like worms • Females 25 to 30cm long • Males 12 to 16 cm long with spirally coiled tail

  6. Morphology • give live birth and the baby worms are called Microfilariae • Microfilariae • Sheathless • 218 to 329µm long • have a long pointed tail

  7. Life Cycle

  8. 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

  9. 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

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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)

  15. Heartworm in Cats vs. Dogs

  16. 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

  17. 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

  18. 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

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

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