Here comes the sun: Are you ready for parasite season?

VettedVetted February 2019
Volume 114
Issue 2

Longer days. More vegetation. Spring brings forth a sense of hope and, at the same time, more stuff to encourage parasite numbers. Here are some answers to what might be on your mind.

Barbulat, Grigorita Ko/

The time for the rise of the parasites begins-acknowledging, of course, that some warmer climates never quite lose them. So we asked a local veterinary clinic for what parasitology-related questions they have and snagged answers from Richard Gerhold, DVM, MS, PhD-always ready to deliver crucial parasite prevention tips.

Do heartworm preventives with efficacy against intestinal parasites work for routine puppy deworming?

Dr. Gerhold: Depending on the active drug in the preventive, the treatment should be effective at removing Toxocara canis (roundworms), Ancylostoma caninum (hookworms) and potentially Trichuris vulpis (whipworms). Ivermectin is not effective against T. vulpis, so animals receiving a preventive with only ivermectin would need a secondary product for treatment of infection with T. vulpis. Furthermore, tapeworm infections would need to be treated with either praziquantel or fenbendazole, depending on the tapeworm species. Finally, if dogs are being treated with ProHeart 6, they will also need to be given a monthly medication to control intestinal parasites.

Are some fleas resistant to flea preventives?

Dr. Gerhold: My overall feeling is that resistance is likely perceived because veterinarians are not educating owners about the need to perform thorough cleaning of the house to remove the larvae and egg stages. (Check out this client handout with house-cleaning tips.)

What are the latest updates on microfilarial resistance to heartworm?

Dr. Gerhold: While there does appear to be some legitimate resistance of Dirofilaria immitis microfilariae to at least some of the preventives, it's a minor issue compared to lack of owner compliance in administering monthly heartworm preventives to dogs and cats. Efforts should be focused on educating owners about the necessity of compliance with monthly administration of heartworm preventive. Furthermore, veterinarians should avoid the use of the slow-kill method for adult heartworms if at all possible. The use of slow kill greatly increases the chances of selecting for resistant strains of D. immitis microfilariae that may be transmitted to other canids.

What are the differences in efficacy between in-house fecal flotation versus outside diagnostic laboratory test versus centrifugation?

Dr. Gerhold: If in-house fecal flotation is being performed using centrifugation and the staff are trained in parasite identification, then this is sufficient for routine parasite detection. In cases where an unknown parasitic egg, larvae or oocyst is observed, fresh fecal samples should be submitted to a diagnostic laboratory employing trained parasitologists to identify the parasites. The use of centrifugation is superior compared with passive flotation for the detection of numerous eggs, oocysts and larvae. Often when centrifugation and passive floatation techniques are done side-by-side on the same sample, observers are surprised to see the increased number of parasite species and quantity of parasites with the centrifugation method.

What do you think of genetically modifying mosquitoes to make them less capable of transmitting diseases?

Dr. Gerhold: I am very much in favor of research to investigate options for genetically controlling vector-borne disease. I see this research as being similar to the release of sterile male screw worm flies that led to eradication of screw worms from the United States. Hopefully there is funding for such research projects in the future to test the efficacy of such genetically modified vectors.

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