Heartworm Society Alert

[kninebirddog]

http://www.heartwormsociety.org/UrgentAlert-8-9-11.pdf

The American Heartworm Society:

Guidance for Heartworm Disease Management

During the Adulticide Unavailability

Background

August 9, 2011: The American Heartworm Society became aware of a pending product unavailability of the only available heartworm adulticide product, IMMITICIDE®, for an undetermined duration.

Because there are no other approved products available for killing adult heartworms, the American Heartworm Society Board and Scientific Committee has developed and approved the following management plan for heartworm positive dogs during this period of adulticide unavailability. While the unavailability persists, heartworm-positive dogs should be managed to achieve three primary goals:

• Reduce potential pathology from the infection.

• Maintain the health of the dog until it can be appropriately treated.

• Prevent additional heartworm infection of the dog.

These goals may be achieved by strict adherence to the following:

• Limit the activity level of the dog to reduce pathology.1,2

• Carefully place the non-protected dog on heartworm prevention.3,4,5,6,7

• Administer doxycycline to reduce pathology and infective potential of heartworms.8

The Management Plan: Heartworm-Positive Dogs and Dogs Not Completing a Full Course of Adulticidal Therapy

1. Verify any positive antigen test by performing a second antigen test, sourced from a different manufacturer. If a dog is confirmed antigen positive or for dogs already initiated on, but not completed adulticidal therapy (due to product unavailability), a microfilariae test should be performed. In rare cases, the administration of heartworm preventives to microfilaremic dogs can result in shock-type reaction. For this reason professional observation is highly recommended.

• If microfilariae are detected, the dog should be pretreated with corticosteroids with or without antihistamines9 and then administered a dose of heartworm preventive (macrocyclic lactone).10

o While all heartworm preventives affect microfilariae, the resulting immunologic reaction of the dog to the microfilariae can vary dramatically.3,4,5,6,7 Therefore dogs should be kept under clinical observation for at least 8 hours following the initial dose of heartworm preventive to allow rapid, appropriate medical treatment should a shock reaction occur.

o Anti-inflammatory pretreatment: Dexamethasone at 0.25 mg/kg intravenously and diphenhydramine at 2.2 mg/kg intramuscularly, or 1 mg/kg of prednisolone orally 1 hour before and 6 hours after administration of the first dose of preventive.9

o Elimination of every single microfilaria is not the goal; the health, safety, and maintenance of the patient is the goal.

o Microfilariae will likely persist following preventive dosing.

o If the positive dog is already on prevention, continue regular monthly oral or topical

dosing or twice yearly injections of preventives.

• If the dog is negative for microfilariae, a heartworm preventive should be

administered.

2. Dogs should then be maintained continuously on heartworm preventive to limit

further infection of the dog until the adulticide product is again available.

3. Dogs should also receive doxycycline at 10 mg/kg BID for 4 weeks. This dosing

should be repeated quarterly until adulticide is available. (Dose may be reduced to 5 mg/kg

BID if tolerance issues exist.)

• Doxycycline has been demonstrated to affect the viability of subsequent heartworm

stages.

• Microfilariae will still be able to infect mosquitoes, but the infective larvae from these

mosquitoes will be less capable of infecting another dog.

• The doxycycline protocol would be 1 month on, 2 months off, 1 month on, 2 months off,

etc.

• The combination of macrocyclic lactone and doxycycline is proven to be more effective

than macrocyclic lactones alone. Research studies have demonstrated macrocyclic

lactone/doxycycline combinations will:

o Shorten the life span, but not eliminate the adult worm infection.

o Lessen the pathology associated with worm death.

o Disrupt heartworm transmission.

4. Restrict ALL activity of the dog! Limit ALL exercise!

• The severity of heartworm disease is directly related to the activity level of the dog.

• As physical activity increases, pathology associated with adult heartworms increases.

5. Any dogs that are symptomatic for heartworm infection should be treated medically

to relieve signs of respiratory distress. Surgical options should be weighed for dogs

exhibiting cardiovascular compromise.

6. When adulticide product is again available:

• Adult heartworms will likely persist in the dogs managed under this protocol.

• Nevertheless, dogs should be retested to revalidate the presence of an adult heartworm

infection.

• If positive, the dog should be appropriately treated for adult heartworms with the

approved adulticidal product.

REMEMBER THE GOALS:

• Reduce potential pathology from the infection.

• Maintain the health of the dog until it can be appropriately treated.

• Prevent additional heartworm infection of the dog.

For further background information considered in development of this management protocol,

refer to the American Heartworm Society’s Current Canine Guidelines under the Veterinary

Resources at www.heartwormsociety.org.