Heartworm Disease PDF 2024

Heartworm Disease Anna McManamey, DVM, DACVIM (Cardiology) VCS 84601 January 12 and January 16, 2024 2 Objectives Diagram the life cycle of dirofilaria immitus in the dog and cat Identify the appropriate stage of HWD in a clinical patient Recognize the classic history, physical exam findings, and pa...

Heartworm Disease Anna McManamey, DVM, DACVIM (Cardiology) VCS 84601 January 12 and January 16, 2024 2 Objectives Diagram the life cycle of dirofilaria immitus in the dog and cat Identify the appropriate stage of HWD in a clinical patient Recognize the classic history, physical exam findings, and pathology associated with HWD in the dog and cat List the diagnostics recommended to diagnose HWD in the dog and cat Recommend the appropriate therapy for HWD in the dog and cat Recommend the appropriate prevention for HWD in the dog and cat Identify resources for health care provider and client education 3 Introduction to Heartworms American Heartworm Society https://www.heartwormsociety.org/ 4 5 Heartworms Dirofilaria immitis Heartworms are primarily a disease of the pulmonary arterial tree Advanced infections result in cardiac 6 D. immitus incidence maps 7 Wolbachia Gram negative bacteria Infect filarial nematodes Symbiotic relationship with D. immitis Results in improved fertility and fortitude of the adult heartworms Wolbachia can also elicit an immune/inflammatory response on its own Wolbachia Surface Protein (WSP) Targets lungs and kidneys Veterian Key 8 D. immitis life cycle Other hosts: Ferrets* Definitive host Wild canines and felines Sea lions Horse Bear Human 9 Stages/Classification of HWD Class I Class II Class III Class IV American Heartworm Society 10 History & Clinical Signs DOG BOTH Asymptomatic* Cough Weight loss Hemoptysis Exercise intolerance Tachypnea Right sided congestive heart failure Syncope Cardiovascular collapse Sudden death CAT Ask about: Vomiting Neurologic signs Travel history Adoption history Preventative history - be specific! 11 Physical Exam – Normal to VERY Sick Body condition score May be cachectic or poor-doing Breathing pattern Normal → dyspnea Lung sounds Crackles and/or wheezes Heart sounds Normal, TR, PI, split S2 Jugular veins distension/pulsation* Abdominal palpation Fluid wave, hepatomegaly 12 Making the Diagnosis 13 ELISA Heartworm Testing SNAP test Detects sexually reproducing female ANTIGEN Nearly 100% specific with great sensitivity Results: Positive or "no antigen detected" Reasons for a false negative Single female or pure male population Immature worm population Improper sample or test handling Antigen-antibody complexes prevent antigen from binding to ELISA test IDEXX | BioNinja 14 Heat Treatment Recommendations Heat-treatment via laboratory *IF clinical signs and other dx strongly suggest HWD* Sample is heated to 104 for 10 minutes Heat-treatment breaks down patient antibodies to free up HW antigen 7.1% of dogs in the shelter setting that were Ag -but MF + had a + Ag after heat treatment (Velasquez et al, 2014) It is NOT recommended to request heat-treatment on routine screening/sampling 15 Heartworm Antibody Test Serology to assess for antibodies to heartworm infection Male or female, larval stages Antibodies can develop as early as 2 months post-infection Represents exposure, not active infections Specificity 98%, Sensitivity 32-89% 16 Microfilaria Testing Blood Smear Modified Knott's Test Either drop on slide straight from syringe and look at feathered edge Ideal for identifying microfilariae Can look at buffy coat in hematocrit tube Best method for distinguishing between microfilariae Every dog should be tested for MF if they are Antigen positive Up to 20% may be MF negative (more if they are on routine ML therapy) 17 Microfilaria Testing 18 HW Testing in the CAT When to test Before starting preventative (academic) If clinical signs are consistent with HWD If monitoring a cat that was previously diagnosed with HWD 19 HW Testing in the DOG Routine screening at wellness visits Before prescribing preventative If there has been a lapse in preventative coverage and/or inappropriate preventative When there are clinical signs If radiographs support a diagnosis of HWD If there is a diagnosis of pulmonary hypertension 20 Recommendations For DOGS: SNAP test AND Microfilaria testing For CATS: SNAP antigen AND Antibody test Usually microfilaria negative* Ideally, have TWO or more positive results before adulticidal therapy* Adulticidal therapy is ONLY used in DOGS Imaging: Thoracic Radiographs CAN BE NORMAL with low worm burdens! Dr. Mac recommends thoracic radiographs in HW positive animals DOG CAT Right sided cardiomegaly Pulmonary arterial dilation Heartworm associated respiratory disease (HARD) Tortuous* pulmonary arteries Pulmonary arterial dilation +/- interstitial pattern Tortuous* pulmonary arteries Pneumonitis +/- interstitial pattern Pulmonary hypertension Pneumonitis R- CHF Semantic Scholar 21 22 MedVet | Scansen, Angiography 2013 23 Scansen, Angiography 2013 24 Scansen, Angiography 2013 Radiographs of Canine HWD (Tjostheim et al. JVC. 2019) 25 HWD in the DOG Rx: sildenafil, pimobendan, doxycycline, prednisone taper, Heartgard “Nugget,” 5 yo FS American Bulldog mix Presented for hemoptysis and respiratory distress Found as rescue 4 months ago; unknown medical history No murmur appreciated on physical exam but diffuse pulmonary crackles noted and marked respiratory effort HW antigen SNAP negative at rDVM Microfilaria positive HW heat treated sample SNAP POSITIVE 26 27 Heartworm Associated Respiratory Disease (HARD) HWD in the CAT Rx: prednisone*, doxycycline, time “Moonshine,” 6 yo MC DSH Presented acute respiratory distress, coughing, and “cardiac arrest” (suspect syncope) Indoor only cat; 1 dog in household Tachycardic, murmur (?), diffuse pulmonary crackles noted with marked respiratory effort HW SNAP, MF negative, normal echocardiogram HW antibody positive 28 Imaging: Echocardiography Assessing for evidence of worms In the PA (most commonly) Assess for presence of pulmonary hypertension Category 5 of PH classification Assess for evidence of right heart failure (cor pulmonale) RV R A LV LA 29 Echocardiography Right ventricular hypertrophy (RVH) Interventricular septal (IVS) flattening Dilated main pulmonary artery (MPA) Histopathology - Changes in the arteries AND the alveoli 30 - Villous arteritis* pathognomonic Nelson. Compendium. 2008. McCracken and Patton. J Vet Path. 1993. 31 Caval Syndrome Caval syndrome patients tend to have severe worm burdens AND high pulmonary artery pressures WITH myocardial dysfunction Caval syndrome patients are SICK The presence of the worms IN THE tricuspid valve cause significant hemolysis Anemic* Icteric* AKI Glomerulonephritis Hemoglobinuria* Death usually occurs within 24-48 hours of diagnosis if no intervention is made 32 Caval Syndrome Treatment HEARTWORM EXTRACTION Remove the obstruction to flow and stop RBC destruction These patients are VERY unstable; need sedation and a local block more than full anesthesia 50% survival through procedure Treat the other pathologies! RBC transfusion if severe anemia Sildenafil if severe pulmonary hypertension Pimobendan and diuretics if in CHF Steroids to treat pneumonitis Diphenhydramine and famotidine to reduce risk of anaphylaxis with worm manipulation Some patients have lasting, irreversible AKI* and/or cardiac disease that needs lifelong management Still require the rest of HW treatment protocol* 33 Heartworm Treatment 34 American Heartworm Society Guidelines for DOGS Goal: treat and eliminate all stages of the heartworm infection These are guidelines for standard infection (Stage I and II) Still needed for Stage III and IV* EXERCISE RESTRICTION** during adulticidal therapy Anti-coagulant therapy is NOT recommended 35 Advanced Stages of HWD in the DOG Severe HWD can result in severe pulmonary hypertension This is a PRESSURE overload on the right heart Eventually, right sided congestive heart failure can develop This is called "cor pulmonale" Treatment Strategy: Treat the CHF --> diuretics, positive inotropes, +/- RAAS inhibition Treat the PH --> sildenafil, oxygen Treat the HWD --> doxycycline, steroid taper, MFilariacide, eventual adulticide Do not forget the Doxycycline! Targets the Wolbachia sp Has anti-inflammatory effects on the lungs Use care in cats Esophageal stricture 36 37 Check MF Status before Treatment If a patient has a high MF burden, they are more likely to have adverse effects from large numbers of MF dying at once* 38 Melarsomine Dihydrochloride Administered as a STERILE* deep IM injection between L3 and L5 Can be painful (even days after injection) The two-injection protocol (label recommends for Class I and II) The three-dose alternate protocol (label recommends for Class III) two injections of 2.5 mg/kg body weight 24 hours apart kills only about 90% of the adult worms. one injection of 2.5 mg/kg body weight followed at least one month later by two injections of the same dose 24 hours apart listed for treating class 3 heartworm disease kills 98% of the worms BUT, the American Heartworm Society recommends the 3-dose protocol for Class I, II, and III of HWD in dogs Keister et al, 1992; Vezzoni et al, 1992. 39 "Slow Kill" Practical answer: Maybe this is okay for very mild infections (ie no radiographic changes or clinical signs) Any methods using continuous monthly administration of prophylactic doses of any macrocyclic lactone alone are NOT RECOMMENDED The adulticidal effect of macrocyclic lactones has been shown to take more than 2 years of continuous administration before adult heartworms are 95% eliminated (McCall et al, 2001). The timing for rigid exercise restriction is unknown with this approach Pathology continues to progress until HW are dead (Rawlings et al, 2001). Potential for selection of resistant subpopulations of heartworms (Bowman, 2012; Geary et al, 2011). 40 Assessing Efficacy Worms will continue dying up to 1 month post-adulticidal therapy HW Antigen test in 6 months to confirm absence of sexually reproducing females If still antigen positive at 6 months, retest at 9 months post-therapy before restarting treatment Also, test for MF 6 months post treatment If positive for MF: may be due to repeat infection (from lack of preventative compliance) maturation of larvae if doxycycline and macrocyclic lactones were not used during adulticidal therapy truly resistant infection* 41 Thromboembolic Complications EXERCISE RESTRICTION IS ESSENTIAL to reduce rate of complication Thromboembolic events typically happen 7-10 days post-injection (can be as late as 4 weeks) Clinical signs: Low grade fever Cough Tachypnea Hemoptysis Exacerbation of right heart failure Treat supportively! Anti-coagulants not strongly recommended as the "thrombus" is the WORM not platelets... 42 HW Treatment in the CAT Steroids are the mainstay of therapy Tetracyclines to kill Wolbachia Adulticidal therapy is not recommended in cats due to lack of knowledge/experience Surgical worm removal is very uncommon due to the low number of adult worms The worm(s) have to be where we can reach them (at least near the main pulmonary artery) IF a cat is HW antigen positive, recommend retesting every 6-12 months to monitor for adult HW death Can take up to 2-3 years in the cat** to die 43 Prevention 44 Prevention in DOGS Macrocyclic Lactones PO: ivermectin, milbemycin oxime Topical: moxidectin, and selamectin Injection: ProHeart 6 and 12 is a slow-release (SR) SQ moxidectin-impregnated lipid microspheres Every 6 months in dogs 6 months or older Every 12 months in dogs 12 months or older Affect MF, L3, L4, and maybe even L5 and adults... Use with caution ivermectin use in MDR-1 dogs* 45 Prevention in CATS Being an "indoor" cat is NOT the same as prevention 25% of HW positive cats were Indoor only Cats are at risk if they live in an area where the disease is endemic in dogs and/or there are mosquitoes PO: ivermectin or milbemycin oxime or topical: moxidectin or selamectin Ideally, year-round treatment 46 Multifactorial Approach CLIENT EDUCATION!! Routine, YEAR ROUND macrocyclic lactone preventative Holistic methods NOT proven Routine testing/screening to identify reservoir patients