Treating Canine Heartworm Disease in Animal Shelters: Practical Management Strategies Natalie Isaza, DVM Grevior Clinical Associate Professor Veterinary Community Outreach Program College of Veterinary Medicine University of Florida The Problem Heartworm disease is common in shelter dogs, especially in the deep south Many rural shelters do not have the resources to treat these animals for heartworm disease; many do not even test for HW infection Many dogs are euthanized in shelters every year across the United States due to heartworm positive status With transportation of heartworm positive animals from rural southern shelters to other parts of the US, there may be an increased risk of heartworm infection for dogs in these areas Canine heartworm has been shown to have developed resistance to macrocyclic lactone drugs like ivermectin (Mississippi delta region of the US) Outline Overview of heartworm disease Epidemiology Heartworm life cycle Discuss the recommendations for heartworm diagnosis, therapy, and prevention from the American Heartworm Society (AHS) Overview of treatment strategies employed by shelters across the United States (AHS-ASV Survey) Practical management strategies for animal shelters Transporting HW positive dogs Puppies What to tell adopters 1
Learning Outcomes Understand characteristics of canine heartworm disease so that infected dogs can be treated effectively Understand the current recommendations for treatment and the challenges faced by animal shelters to provide these treatments in a shelter setting Be able to design treatment protocols that are feasible for your shelter, keeping in mind the risks and benefits Understand how to counsel adopters about heartworm disease Heartworm Disease Caused by the filarial parasite Dirofilaria immitis Transmitted via infected mosquitoes of the genus Aedes (primarily A. sierrensis in the western US, and A. albopictus in the southern US and east coast) Has been found in all 50 states, as well as the US territories of Puerto Rico, US Virgin Islands, and Guam Heartworm Disease Definitive hosts are the domestic dog and some wild canids Cats and ferrets are less suitable hosts, but may serve as a limited source of infection for mosquitoes Prevalence in shelter dogs as high as 70% in endemic areas 2
Heartworm Incidence: Private Veterinary Practices Canine Heartworm Disease Prevalence of positive test results Private Veterinary Practice Region Northeast <1% Midwest <1% Southeast 4% West 1% Overall Prevaence 1% Mean Percent Animal Shelters 15% of Shelter Dogs in Florida Canine Heartworm Disease Heartworms are Endemic in the United States due to Environmental changes that are favorable for mosquitoes Expansion of wild canid populations Transportation of heartworm positive dogs 3
Heartworm Life Cycle Mosquito Bites Infected Dog L4-L5 (takes 3-4 months); adults (L5) produce microfilaria as early as 6 months post-infection Microfilaria (L1) Ingested with Blood Meal In Dog: L3 Larvae deposited into soft tissue with blood meal (3-12 days to molt to L4) In Mosquito: L1-L3 (takes 2 weeks); L3 is infective stage Heartworm Life Cycle Other Factors Development in the mosquito from L1 (microfilaria) to L3 (infective stage) is temperature dependent, and ceases below 57 F Micro-environments in urban areas created by reflected heat from buildings may allow for development to L3 in spite of cold temperatures Many mosquito vector species overwinter as adults Infection rates of mosquitoes around kennel structures have been shown to be as high as 70% Risk of infection is always present! Information obtained from the American Heartworm Society, Canine Guidelines, 2014 Heartworm Disease Clinical Signs: Dependent on severity and duration of infection Include weight loss, exercise intolerance, cough, and dyspnea Abnormal cardiac auscultation findings may include rightsided heart murmur (tricuspid insufficiency) and gallop rhythm Right heart failure: jugular venous distention, hepatosplenomagaly, and abdominal distention due to ascites Pulmonary thromboembolism can result in hemoptysis and sudden death The vast majority of HW positive dogs are asymptomatic! 4
Heartworm Disease Classifying the severity of heartworm disease by symptoms: Class 1: Positive heartworm test; asymptomatic Class 2: Positive heartworm test; mild exercise intolerance Class 3: Positive heartworm test; moderate to severe exercise intolerance, cough Class 4: Positive heartworm test; ascites/right heart failure=caval Syndrome Canine Heartworm Disease Diagnosis Prevention Treatment Heartworm Diagnosis Antigen Tests Detects the presence of female worm antigen Not necessary to test dogs prior to 7 months of age Many tests are available 5
Heartworm Diagnosis Antigen Tests Detect female heartworm antigen Identify most occult infections (no microfilaria present) Most tests available are nearly 100% specific (true negative rate) Most have high sensitivity (true positive rate), but sensitivity of each test varies depending on worm burden Color intensity cannot reliably predict worm burden Test results should be recorded as positive or NAD (no antigen detected), and never recorded as negative Heartworm Diagnosis Microwell Tests All of the well tests allow for multiple tests to be run at the same time Dirocheck (Synbiotics) Petcheck (IDEXX) These tests may be more cost effective for shelters if testing large numbers of dogs daily Heartworm Diagnosis Microfilaria Testing AHS recommends performing both ELISA and microfilaria tests Important if there is a high degree of suspicion that the animal is positive, or if the heartworm history is unknown (shelter dogs!) Testing for both female antigen and microfilaria Validates serologic results Identifies the patient as a reservoir for infection Alerts to high microfilarial burden, which could precipitate a severe reaction after administration of a microfilaricide 6
Heartworm Diagnosis Microfilaria Testing Blood smear Buffy coat Insensitive for detecting low numbers of microfilaria; may be confused with Acanthocheilonema (formerly Dipetalonema) Modified Knott s Test: preferred method; allows differentiation between filarial species D A Photo from AHS Canine Guidelines 2014, Dr. Byron Blagburn Heartworm Diagnosis And another wrinkle Some positive dogs may have antigen-antibody complexes, resulting in a false negative antigen test (as many as 7% of dogs in endemic areas) These dogs will be antigen negative but microfilaria positive Heat treatment of serum prior to testing may help break these complexes resulting in a more accurate antigen test result, but routine heat treatment of all samples is not recommended Heartworm Diagnosis Heartworm Testing: When? All dogs should be tested annually Test dogs prior to changing heartworm preventives Test dogs if there is any lapse in heartworm preventive Radiographs, cardiac echo, bloodwork if indicated Not practical for most animal shelters 7
Heartworm Prevention Important for all dogs to be on heartworm preventive year round, especially if in endemic areas Annual testing is recommended even if on year-round preventive By reducing the reservoir population of heartworm in a community, there is a corresponding decrease in prevalence of infection among unprotected dogs What about puppies? According the American Heartworm Society All puppies should be started on preventatives at by at least 8 weeks of age If over 8 weeks of age when first given preventative, test for heartworm infection 6 months after the initial dose Heartworm Prevention Mosquito control is also very important New area of interest for prevention of disease spread A recent study showed that mosquito repellants/insecticides were more than 95% effective in preventing transmission of microfilaria to mosquitoes Some topical flea and tick products also act as mosquito repellants for dogs 8
Heartworm Prevention Macrocyclic Lactones Ivermectin (Heartguard ) Milbemycin oxime (Interceptor ) Moxidectin (Advantage Multi ) Selamectin (Revolution ) All affect L1 (microfilaria), L3, L4, and adult heartworms Safe when used according to label directions 30 day dosing interval for oral and topical products Heartworm Prevention Oral Administration Ivermectin products Milbemycin products Topical Administration Moxidectin products Selamectin products Parenteral Administration Moxidectin product Heartworm Prevention Many shelters use Ivermectin 1% (Noromectin, Ivomec ) for monthly heartworm prevention Remember that this use is off-label Dose is 6 µg/kg (0.006 mg/kg) for HW prevention (extremely low dose, so difficult to dose without diluting first) Use with extreme caution in herding breeds due to sensitivity to the drug 9
Heartworm Prevention All stages of the heartworm are susceptible to macrocyclic lactones, although L4, juvenile L5, and adult L5 worms have much less susceptibility to these drugs Resistance Recent studies have shown that genetic changes seen in heartworms is related to resistance to heartworm preventives Currently these changes have been seen in heartworms from the Mississippi Delta region of the country Resistance First reported in a dog rescued from Hurricane Katrina Dog remained microfilaremic despite adulticidal treatment and repeated treatment with macrocyclic lactones Resistant microfilariae (MP3 isolate) exhibit an allele on the P- glycoprotein gene that differs from the general population MP3 isolate has been shown to have decreased susceptibility to single monthly doses of ivermectin, milbemycin, and selemectin MP3 isolate was susceptible to three consecutive monthly doses of milbemycin, and one single dose of moxidectin Bourguinat, et. al., Veterinary Parasitology, 2011. Blagburn, et. al, Veterinary Parasitology, 2011. 10
AHS Recommended Treatment Adulticide Therapy Melarsomine dihydrochloride (3 dose protocol) Manual removal of adult heartworms (caval syndrome) Adjunct Therapies: Steroids NSAIDs Doxycycline Macrocyclic Lactones AHS Recommended Treatment Days 0-59 Exercise restriction 4 week course of steroids if symptomatic Monthly heartworm preventive 4 week course of doxycycline Days 60-91 Adulticidal treatment with melarsomine (days 60, 90, 91) 4 week course of steroids Limit activity to leash walks; cage rest Continue exercise restriction for 6-8 weeks Melarsomine (Immiticide ) The Evidence Field Studies Mild infection 2 dose protocol: 90-98% of dogs negative at 4 months Severe infection 3 dose protocol: 89-100% of dogs negative at 4 months Laboratory Studies 1 dose resulted in death of 52% of adult worms 2 doses resulted in death of 90% of adult worms 3 doses resulted in death of 98-99% of adult worms 11
Melarsomine (Immiticide ) Review of Field and Laboratory Studies 2 or 3 dose protocol Efficacy confirmed by antigen test or necropsy Weighted Average Efficacy 2 dose protocol: 88% 3 dose protocol: 89% Conclusion: 10% of dogs treated will have fewer than 1 heartworm remaining following treatment with either the 2 or 3 dose protocol Melarsomine (Immiticide ) Arsenical compound, so very low margin of safety Dose in dogs is 2.5 mg/kg; LD50 in dogs is 7.5 mg/kg One of two Black Label drugs in veterinary medicine Complications include: Pain/swelling at injection site Ataxia, paresis, or paralysis of the pelvic limbs Fever, lethargy, inappetance Coughing/Hemoptysis Pulmonary thromboembolism Sudden death Melarsomine (Immiticide ) Riley 12
Melarsomine (Immiticide ) Adjunct Therapies Steroids (Prednisone) Used to control clinical signs of pulmonary thromboembolism Given in diminished, anti-inflammatory dosing: 0.5 mg/kg BID X 7 days 0.5 mg/kg SID X 7 days 0.5 mg/kg EOD for 1-2 weeks Recommended for all HW positive dogs in endemic areas Adjunct Therapies NSAIDS NSAIDS like Previcox and Rimadyl may be used to alleviate pain from the injection site Aspirin is NOT recommended Used for its antithrombotic effect; may actually be contraindicated 13
Adjunct Therapies Doxycycline Kills the obligate, intracellular, gram-negative bacteria Wolbachia pipientis Because the bacteria is endo-symbiotic with D. immitis, use of Doxycycline for 30 days eliminates L3 and L4 larvae, as well as juvenile worms In dogs with adult infections, the use of doxycycline gradually suppresses microfilaremia Microfilaria from dogs treated with doxycycline were not able to develop into adult heartworms Recommended dose is 10 mg/kg BID X 4 weeks (prior to administration of melarsomine) Adjunct Therapies Macrocyclic Lactones Can be used 2-3 months prior to adulticide therapy to minimize susceptibility gap Accomplishes three things: Reduces new infections Eliminates existing susceptible larvae Allows older worms to mature to a point where they are susceptible to melarsomine Adjunct Therapies Macrocyclic Lactones/Doxycycline Combined, these drugs suppress emrbyogenesis and weaken adult heartworms Doxycycline in combination with macrocyclic lactone provides more rapid adulticidal therapy than macrocyclic lactone alone This combination also more efficiently reduces the number of Wolbachia organisms Used in cases where arsenical therapy is not possible or contraindicated Doxycycline 10 mg/kg BID x 4 weeks, with concurrent monthly heartworm preventive 14
Adjunct Therapies Italian study (Grandi, et.al., 2011) of 11 dogs: Positive dogs received macrocyclic lactone-pyrantel combination every 15 days, with doxycycline at 10 mg/kg BID for 30 days This drug combination was shown to kill 100% of adult heartworms in all study dogs by day 300 Alternatives to Doxycycline Minocycline 10 mg/kg PO BID X 4 weeks Disadvantage: Causes nausea and vomiting in many patients Azithromycin 5 mg/kg PO BID X 10-20 days* Z pack ; can cause fatal arrhythmias in people Rifampin 10-15 mg/kg PO or IV BID, prn* Used to treat tuberculosis in people *Doses provided by Dr. Byron Blagburn Adjunct Therapies Doxycycline in combination with macrocyclic lactones provides more rapid adulticidal therapy than with macrocyclic lactones alone! + = Dog! 15
Slow-Kill Method AHS defines this as the use of only macrocyclic lactones in heartworm positive dogs The use of these drugs reduce the lifespan of juvenile and adult heartworms; older worms are less susceptible and take longer to die Presence of adult worms in the pulmonary vasculature continues to cause damage Damage worsens with exercise: exercise restriction? May take up to 2 years to eliminate adult worms using this method May lead to resistant sub-populations of heartworm Post-Adulticide Testing Antigen testing should be performed 6 months post-treatment for dogs that received macrocyclic lactones prior to or concurrent with adulticide therapy For dogs treated immediately after diagnosis and not given heartworm preventives until after the adulticide therapy, testing should be performed at 7 months following the initial dose of heartworm preventive Microfilaria testing should be performed concurrently Elimination of Microfilariae Current protocols using doxycycline in combination with preventive doses of macrocyclic lactones has eliminated the need for post-adulticidal elimination of microfilariae In instances where doxycycline is not used, treat to eliminate microfilariae 3-4 weeks following adulticide therapy Advantage Multi used prior to adulticide therapy can also eliminate microfilaria (no adverse reactions reported) Elimination of microfilaria is very important in limiting the number of reservoir hosts 16
Elimination of Microfilariae Macrocyclic lactones used as microfilaricides: Milbemycin oxime (Interceptor ) at labeled preventive dose Ivermectin at 50 µg/kg (almost 10 times the preventive dose) Both Ivermectin and Milbemycin should be used with caution in dogs with high microfilaria counts! Moxidectin (Advantage Multi ) topical preparation at labeled preventive dose No adverse reaction has been seen with this preparation FDA approved for eliminating microfilaria Treating Shelter Dogs Financial considerations Length of stay Decisions on who to treat Treating Shelter Dogs Are animal shelters treating dogs with heartworm infection? Survey of 1483 animal shelters in Alabama, Florida, Georgia, and Mississippi (Colby, et. al., Veterinary Parasitology, 2011) 443 shelters (30%) tested dogs for heartworm infection 174 (39%) treated all infected dogs 217 (49%) treated some infected dogs 52 (12%) did not treat 17
Treating Shelter Dogs What treatment protocols are used in animal shelters? In shelters that treated (Colby, et.al., 2011): 139 (43%) used a two-dose melarsomine protocol 113 (35%) used a three-dose melarsomine protocol 70 (22%) used long-term, low dose ivermectin Treating Shelter Dogs 2014 survey conducted by the AHS to the ASV Shelter Vet list serve on testing, treatment and prevention protocols* 105 respondents 61% were open admission shelters 36% were limited admission shelters 41.6% of shelters tested all dogs Endemic areas 48.5% of shelters tested some dogs Adoption candidates Health concerns 9.9% of shelters did not test *DiGangi, Isaza, Polak, and Smith-Blackmore; unpublished data Treating Shelter Dogs For prevention, the majority (66%) of respondents indicated the use of monthly oral macrocyclic lactone formulations 20% of respondents used off-label ivermectin 18
Treating Shelter Dogs Most of the shelter veterinarians surveyed indicated that at least some of their heartworm positive dogs were treated Dogs deemed poor adoption candidates due to behavioral or other medical problems were least likely to receive treatment Treating Shelter Dogs Most veterinarians surveyed indicated all positive dogs received the three-dose melarsomine protocol Some reserved three-dose protocol for dogs under 25 pounds Only 7.2% indicated they used monthly ivermectin alone Other included doxycycline therapy with monthly ivermectin Treating Shelter Dogs Many shelters also use adjunctive therapy, including 80% using doxycycline or its equivalent Other treatments included analgesics post-treatment (NSAIDS, tramadol), diphenhydramine, and dexamethasone 19
Treating Shelter Dogs What about Elective Surgeries? If a patient is asymptomatic, it is best to perform spay/neuter surgery prior to adulticide therapy If symptomatic or with Class III disease, treat first If not spayed or neutered prior to treatment, wait 6-8 months following treatment before performing procedure Make sure dog is heartworm negative prior to surgery Treating Shelter Dogs For Transported Animals: Best to re-test all dogs entering your shelter Repeat both the antigen test and microfilaria test Treat all dogs with Advantage Multi upon arrival Monthly macrocyclic lactone administration can suppress antigenemia in dogs up to 9 months post-infection! Expense of Treatment Melarsomine dihydrochloride (Immiticide ): UF cost is $9.73 per ml ($486.75 for 5 boxes, 10 ml each) Three-dose protocol for a 22kg dog would cost $58 Doxycycline: Used to be free at local pharmacy; now costs $342 for 60-100mg tablets Minocycline: 50 mg capsules (100 count) $16.45; 100 mg capsules (50 count) $17.98 Macrocyclic lactone (Heartguard Plus ): $52.99 at 1-800- PetMeds for 6 month supply (51-100 pounds) Ivermectin 1% (Noromectin ): $21.99 for 50 ml on Amazon 20
Obstacles Many shelters cannot even afford to test dogs, much less treat them If they do treat, many use the slow kill method AHS discourages the slow kill (macrocyclic lactones alone) method, with potential for development of resistance the primary concern Slow kill using macrocyclic lactones/doxycycline combination may be a better alternative, but dogs must still be exercise restricted for months to years to prevent further damage to the pulmonary vasculature Choices No treatment Not recommended due to ongoing pulmonary damage and potential for reservoir host Slow Kill method with macrocyclic lactones alone Not recommended due to ongoing pulmonary damage and potential for reservoir host; also development of resistance Slow Kill method with macrocyclic lactones plus doxycycline or equivalent Better, but worms are still causing pulmonary damage; also strict exercise restriction for months to years Two-dose adulticide therapy Less expensive; best for asymptomatic dogs Three-dose adulticide therapy Best for symptomatic dogs What s a Shelter Vet to Do? 21
Vindication! NAVC 2014* Evaluation of ~350 dogs treated for heartworm infection at NCSU Developed protocol for dogs belonging to low-income families following Hurricane Floyd in 1999 No pre-treatment blood work or radiographs Two-dose protocol Two fatalities (1 CHF and 1 caval syndrome) *Data from Dr. Kelli Ferris, presented by Dr. Clarke Atkins at NAVC 2014 Vindication! When to use the two-dose method:* Financial concerns (shelters!) Young and apparently healthy dogs Dogs with known short exposure in area of low prevalence Dogs that have already undergone adulticide therapy Dogs that can be exercise restricted *From Dr. Clarke Atkins, NAVC 2014 UF Veterinary Community Outreach Program Started in 2003 as the UF Shelter Medicine Program 1 faculty 0 veterinary technicians 5-7 enthusiastic veterinary students! Began treating heartworm positive dogs at Alachua County Animal Services in late 2004 From 2004 through 2016, the program has treated over 700 dogs for heartworm infection 22
*FOR UF USE ONLY* Cage #: Age: Mos. / Yrs. Sex: Male Female Neutered Intact Name: Species: Canine Feline Breed: Color: Rescue Group: I certify that the above named animal, owned by the nonprofit animal rescue agency, is presented for heartworm adulticide treatment. Permission is hereby granted to perform such treatment, with sedation if deemed necessary. I understand the risks associated with these procedures, including injection site pain, infection, paralysis, cough, respiratory distress, and death. Furthermore, I have reviewed and understand the recommendations regarding management of heartworm infected dogs by the Veterinary Community Outreach Program. Signed: Print Name: Date: Injection #1 Is the patient currently on any medications? NO YES Date: Weight (kg): Immiticide (ml): Previcox (mg): Physical Examination: Cage Number: Examiner s Initials: Supervising DVM HR: RR: Temp: BCS: Injection #2 Is the patient currently on any medications? NO YES Date: Weight (kg): Immiticide (ml): Previcox (mg): Physical Examination: Cage Number: Examiner s Initials: Supervising DVM HR: RR: Temp: BCS: Injection #3 Is the patient currently on any medications? NO YES Date: Weight (kg): Immiticide (ml): Previcox (mg): Physical Examination: Cage Number: Examiner s Initials: Supervising DVM HR: RR: Temp: BCS: Notes: L R 9/6/2016 Heartworm Treatments UF Veterinary Community Outreach Program No routine pre-treatment blood work or radiographs CBC/chemistries occasionally done for older dogs Majority of dogs are asymptomatic for heartworm disease Heartworm Treatment Record Heartworm Treatments Current VCOP Protocol Recommend 4 weeks of Minocycline at 10 mg/kg PO BID prior to adulticide therapy Recommend concurrent administration of macrocyclic lactone Two-dose protocol of Immiticide, recommended for asymptomatic dogs Three-dose protocol of Immiticide, recommended for dogs under 10 kg and symptomatic dogs; veterinarian s call NSAIDS (Previcox or Rimadyl ): one dose given at time of injection Additional pain medication as indicated (Tramadol ) Sedation only when necessary (Ace/Butorphanol or Dexdomitor /Butorphanol in extreme cases) Heartworm Treatments Our tools for distraction! 23
Heartworm Treatments Cost for treatment for a 25 kg dog: Minocycline 250 mg PO BID X 4 weeks = $49 Melarsomine 3-dose protocol = 7.5 ml Immiticide = $73 2-dose protocol = $48 Heartguard Plus 1 dose = $9 Total: $131 (3-dose) or $106 (2-dose) Heartworm Treatments UF VCOP: Complication rate very low 5 % complication rate Majority are pain and swelling at injection site 1 % death rate No statistical difference in male vs. female, 2 or 3 dose protocol, age at treatment Risk vs. Benefit Heartworm Diagnosis Testing all dogs (antigen + microfilaria) Risk: expense, time, technical skill Benefit: identifies all positive animals Testing only some dogs (antigen + microfilaria) Risk: miss some heartworm positives; technical skill Benefit: less expensive Microfilaria testing only Risk: poor sensitivity; not recommended as sole testing method Benefit: inexpensive No testing: Risk: miss all heartworm positives; increased disease spread Benefit: least expensive and time consuming 24
Risk vs. Benefit Treatment No Treatment Risk: Worms within the pulmonary vasculature continue to damage tissue; difficult to adopt Benefit: No expense related to treatment Two-dose protocol Risk: May not kill all adult heartworms; less safe for symptomatic dogs Benefit: Shorter treatment time means less time in the shelter; less expensive Three-dose protocol Risk: Expensive; length of stay increases Benefit: Safest method; recommended by AHS Risk vs. Benefit Heartworm Prevention No Prevention Risk: dogs will become infected Benefit: no expense Avermectin Products (Heartguard, Interceptor, Advantage Multi ) Risk: expensive; must use with caution in HW positive dogs Benefit: safe for all dog breeds; many also kill internal parasites Off-label Ivermectin Risk: low margin of safety; easy to overdose (especially in herding breeds who are sensitive to these drugs) Benefit: inexpensive Risk vs. Benefit Mitigate the Risks: Prescribe treatment based on the severity of disease No clinical signs: 2-dose protocol Clinical signs: 3-dose protocol Use adjunctive therapies Always use doxycycline or equivalent Always use monthly preventive Use prednisone in endemic areas or with clinical signs of heartworm disease Consider alternative protocols: doxycycline + ivermectin Immiticide shortage Asymptomatic dogs Shelters where length of stay is less important 25
What about adopters? If adopting a heartworm positive dog Discuss treatment options Immiticide therapy 2 dose 3 dose Maintain all HW positive animals on preventatives, with one month of Doxycycline/Minocycline until treatment begins Exercise restriction imperative Majority of complications stem from increased activity What about adopters? If heartworm negative at adoption Recommend re-testing in 6 months If positive and the dog is returned, develop treatment plan according to the resources of your shelter Maintain all dogs in your shelter on monthly heartworm preventatives Don t forget about mosquito control! Treatment Outcomes Duncan 3 year old, M/N, Min Pin 4.3 kg Presented with Grade III murmur Referred to cardiology for echo Manually extracted 54 adult heartworms Holds record at UFCVM for most worms removed per kg body weight! 26
Treatment Outcomes Bellamy 4 year old, M, Chihuahua mix 5.0 kg Negative heartworm test at ACAS (Dirocheck ) Presented for neuter; grade III murmur ausculted Referred to cardiology Echo showed numerous adult heartworms Re-tested with IDEXX SNAP: Negative! Treatment Outcomes Tiger 3 year old, M/N Chihuahua 3.0 kg 3-dose protocol in February and March, 2009 Re-tested October 2009: IDEXX SNAP positive Re-treated with adulticide therapy Conclusions Treatment plans vary among different sheltering agencies If no funding is available for 3-dose adulticide therapy, consider 2-dose therapy With melarsomine shortages, consider macrocyclic lactones plus doxycycline or equivalent Best not to use macrocyclic lactones alone due to resistance issues and length of treatment Strict exercise restriction is key to a successful outcome 27
References American Heartworm Society, Canine Guidelines, 2014. Colby, et. al., Diagnosis, treatment, and prevention strategies for canine heartworm infection in animal sheltering agencies; Veterinary Parasitology, 2011. Polak and Smith-Blackmore; Animal Shelters: Managing heartworm infections in resource scarce environments; Veterinary Parasitology, 2014. Bourguinat, et. al., Macrocyclic lactone resistance in Dirofilaria immitis; Veterinary Parasitology, 2011. Grandi, et. al., A combination of macrocyclic lactone and doxycycline is adulticidal in Dirofilaria immitis; Veterinary Parasitology, 2011. Thank You 28