Heartworm Flashcards
Where does canine dirofilaria immitis reside?
Pulmonary arteries and occasionally the right ventricle
After the mosquito bites the dog, what happens?
L3, the infective stage, enter the wound and molt to L4 in SQ tissues between 3-12 days after infection. The l4 migrate through the tissues and molt to immature adult within 45-70 days post infection. L3 and L4 are not found in the circulatory system! Immature adults enter the circulation; microfilariae are deposited within 6-7 months (PPP).
Does transplacental transmission in dogs occur?
Yes but the worms will not mature.
What’s the main pathological sign in dogs?
Progressive pulmonary hypertension–>lung disease. Caval Syndrome can occur.
What is an important bacteria in heartworm?
Wolbachia pipientis-symbiotic, Gram -, released in worm death, bacteria and endotoxns exacerbate lung injury-removal lessens lung pathology.
What’s Caval Syndrome?
Acute disease caused by immature heartworms maturing at the same time and occurring in the right atrium, tricuspid, posterior vena cava. Sudden onset, rapidly fatal
What do all commercial antigen tests detect?
Female uterine antigen, do not test dogs prior to 7 months old.
How do you get false negative tests?
Low worm burden, immature females, male only infections, not allowing tests to warm to room temp, immune complexes binding Ag (can heat serum to avoid this)
How do you get false positive tests?
well tests due to inadequate washing, cross reaction with other antigens such as Spirocerca lupi, test error, residual circulating antigens
What’s the difference between these microfilariae and A. spp. ones?
These are OVER 270um and have an anterior tapered body
What are occult infections?
Adults are present but no microfilariae. Prepatent, unisex, drug reduced, or immune mediated clearance
What would you see on an echocardiogram?
Double line where worm is
What are all heartworm preventives?
Macrocyclic lactones
Give the drugs and dosages
Ivermectin, oral, 6ug/kg monthly; milbemycin oxime, oral, 0.5mg/kg monthly; moxidectin 0.17mg/kg six month injectable; moxidectin/imidacloprid 2.5mg/kg and 10mg/kg monthly topical; selamectin, topical, 6mg/kg monthly
What two products provide a reach back and forward effect?
ProHeart and Advantage Multi
What is the standard treatment for dogs?
Day 0-1: diagnose and verify, do a work up, administer doxy and prednisone if clinical signs; Day 30: preventive; Day 60: preventive, injection of melarsomine and prednisone for 4 weeks, exercise restriction; Day 90-91: preventive, 2 injections of melarsomine 24 hours apart, prednisone for 4 weeks, exercise restriction for 6-8 weeks; antigen test 6 months after 3rd melarsomine injection
Slow kill therapy
monthly use of macrocyclic lactones can result in unpredictable worm death, antigen negative dogs may still actually be positive
Is this disease zoonotic?
Rarely, may look like TB on an x-ray so need to do surgery
Can cats get this?
Yes at a lower rate, PPP 7-8 months because cat is resistant
Heartworm associated respiratory disease
Two stages. Stage 1: 3-4 months after infection, lung has intense inflammation and asthma-like symptoms, activation of PIM in lung leads to acute inflammatory reaction with eosinophilic and alveolar reactions (With stage 1 there may be no mature worms and still be life threatening!); stage 2: 1-3 years after infection, mature parasite and may be no clinical signs (downregulate PIM) but when worms die, the lung is inflamed and PIM leads to intense reaction->acute respiratory distress syndrome because of lung injury
What are the two serological methods for feline heartworm?
Female uterine antigen and antibody against molting larvae; excellent because low worm burden, male only infections, symptomatic immune infections, immune complexes binding antigen
How is antibody testing done in the cat?
Produced by cat in response to migration of L3/L4. Positive titers detected 1-3 months after infection. Monthly macrolide preventives can induce an antibody response even if the cat is actually negative. The cat has been exposed to the worms even if not currently infected if positive
What is the treatment for cats?
DO NOT use melarsomine, it is toxic! Do mechanical removal and supportive care, signs are not good (prednisone for lung disease)
What are the prevention doses for cats?
Selamectin, topical, 6-12mg/kg; moxidectin, topical, 1mg/kg (2.5x lower), ivermectin, oral, 24ug/kg (4x higher); milbemycin oxime, oral, 2mg/kg (4x higher)
