Total parasite control: Piecing the puzzle together (Proceedings)

Preventive health care, including the prevention of common parasitic infections in cats and dogs, is an approach that is relatively easy to accomplish. Veterinarians and pet owners must realize that proper selection of parasiticides will not only prevent heartworms but also can prevent a variety of internal and external parasites. This approach has been advocated by the Companion Animal Parasite Council (CAPC; www.capcvet.org). CAPC recommends "year-round treatment with broad-spectrum heartworm anthelmintics that have activity against parasites with zoonotic potential." The council also states: "Pet-owner awareness of heartworms and fleas can serve as the foundation for effective prevention and control of other parasites." These recommendations should be adopted for both cats and dogs.

When beginning a parasite control program it is important to find the foundation parasite from which the success of the program hinges. The foundation parasite may be the most common, the most pathogenic or of the most concern to the client. The foundation parasite is the one disease that you and your clients recognize must be included in your parasite control program. Therefore the foundation parasite in dogs is often Heartworm, but in other areas other parasites such as ticks and the diseases they transmit may also resonate with pet owners. While cats are not as commonly afflicted with heartworms as dogs the increased awareness of the pathology and potentially deadly nature of heartworm disease in cats1,2 may allow D. immitis to rise to the forefront of concern with many clients. However, this author feels that fleas are often the foundation parasite for a parasite control program in cats.3 However, practitioners must use their knowledge and experience to choose the foundation parasite for cats and dogs in their area or even for an individual pet and client.

Next it is important to remember that while we might focus initially on prevention of a "foundation" parasite, we must stress to the pet owner that we are actually implementing a "broadspectrum" parasite prevention package. Explain that not only will we be preventing heartworm disease in dogs, but we will also potentially be controlling fleas, ticks, lice, certain mites, and several common intestinal nematodes. In addition we will be reducing the chance that their dog could transmit a parasitic disease to them or other members of their family. Similarly in cats, we might tell them we will try to ensure that their cat and home does not become flea infested, but we will also be preventing their cat from becoming infested with ear mites, face mange, lice, intestinal nematodes and potentially deadly heartworm.

The program often begins with broad-spectrum heartworm medications that also prevent several common intestinal parasite infestations. Because prevention of heartworm in cats and dogs using macrolides is well documented, this article will focus on the epidemiology and prevention of the other common parasites of cats and dogs that can be controlled using monthly heartworm medications. Products currently approved in the United States and Canada are Advantage Multi (Bayer; imidacloprid:moxidectin, 10 mg/kg:1.0 mg/kg cats; 10 mg/kg:2.5 mg/kg dogs), Heartgard (Merial; oral ivermectin, 24 μg/kg cats; 6 μg/kg dogs), Heartgard Plus for dogs (Merial; oral ivermectin:pyrantel pamoate, 6 μg/kg:5mg/kg (Also Iverheart brands), Interceptor (Novartis; oral milbemycin oxime, 2.0 mg/kg for cats; 0.5mg/kg dogs), Revolution (Pfizer; topical selamectin, 6 to 12 mg/kg) and Sentinel for dogs (Novartis; oral milbemycin oxime:lufenuron, 0.5mg/kg:10mg/kg). These products can be used alone or in combination with other drugs and insecticides to prevent a variety of canine and feline parasites.

Internal Parasites

Many pet owners do not want to think their cat or dog, a member of their family, may have preyed on a mouse, bird or other animal. However, this natural predator–prey relationship is a common mode of transmission of many feline parasites, including Alaria spp., Ancylostoma tubaeforme, Cystoisospora spp. (Isospora) (, Physaloptera spp., Sarcocystis spp., Taenia taeniaeformis, Toxocara cati, Toxascaris leonina, and Toxoplasma gondii.3 Similarly many parasites of dogs can be acquired through predation, including Alaria spp., Cystoisospora spp.( Isospora), Physaloptera spp., Sarcocystis spp., Taenia spp., Toxocara canis, and Toxascaris leonina.4-5

Toxocara sp.

Predation on infected paratenic hosts is commonly underestimated by veterinarians and likely completely unknown by most pet owners as a mode of Toxocara spp. transmission. Larvae commonly become encysted in the tissues of chickens, cockroaches, earthworms, and mice when they ingest infective larvated eggs in feces or contaminated soil. Similarly children may also become infected with somatic tissue stages of T. cat or T. canis, which can cause visceral or ocular larva migrans. In addition cats and dogs become infected after ingesting larvated eggs.

Three of the broad-spectrum heartworm medications currently approved for use in cats are effective in eliminating T. cati; oral milbemycin6, topically applied selamectin7 and the topically applied imidacloprid–moxidectin formulation8.

Several of the broad-spectrum heartworm medications that are currently approved for use in dogs are effective for the elimination of T. canis including the imidacloprid:moxidectin topical formulation,9 the oral ivermectin/pyrantel pamoate formulation,10 oral milbemycin oxime,11 and the oral milbemycin oxime/lufenuron formulation.12 In addition the oral ivermectin/pyrantel pamoate, the topical imidacloprid:moxidectin and the oral milbemycin formulations are also labeled for Toxascaris leonina.

Ancylostoma sp.

In cats larvae may be ingested, penetrate the skin or rodents with encysted larvae may serve as paratenic hosts, but there is no evidence for either transmammary or transplacental transmission of A. tubaeforme in cats.13 All of the broad-spectrum heartworm medications approved for use in cats in the U.S. and Canada are effective in eliminating A. tubaeforme.9, 14,15 Similarly A. caninum which is an important parasitic disease in dogs and a potentially life threatening disease in puppies following transmammary transmission, can be effectively managed with several of the broad-spectrum heartworm medications including the imidacloprid:moxidectin topical formulation,16 the oral ivermectin/pyrantel pamoate formulation,17 oral milbemycin oxime,18 and the oral milbemycin oxime/lufenuron formulation.

It should be remembered that when these formulations are administered as approved, the dog or cat is essentially "dewormed" on a monthly basis. If a pet is frequently exposed to infective third-stage larvae of Ancylostoma spp, the worms can mature and deposit eggs between monthly applications, given that the prepatent period of Ancylostoma spp. can be as short as 2 to 3 weeks. However, monthly application should prevent development of hookworm disease. Uncinaria sp. a mildly pathogenic hookworm species can be controlled by the administration of broad-spectrum heartworm medications that contain milbemycin, moxidectin or pyrantel.

Trichuris vulpis

T. vulpis is a pathogenic parasite of dogs that can produce mild to severe blooding diarrhea and chronic debilitation. This parasitic disease can be controlled by the monthly administration of broad-spectrum heartworm medications that contain milbemycin and the imidacloprid/moxidectin formulation also label claims against whipworms.

Overview of Internal Parasite Prevention

Several broad-spectrum heartworm medications are effective in controlling Toxocara spp. and Ancylostoma spp. but cats and dogs may become infected with a variety of internal parasites against which these formulations may not be effective. Therefore, fecal examinations utilizing a centrifugal procedure should be performed two to four times during the first year of the pet's life and one to two times annually as an adult depending on the pet's health and lifestyle factors (www.capcvet.org). In addition for pet health and to minimize egg shedding kittens should be given biweekly anthelmintic treatments beginning at 3 weeks of age. When cats reach 8 or 9 weeks of age, they can be put on a monthly broad-spectrum heartworm medication. Puppies should be administered anthelmintic treatments at 2, 4, 6, 8, and 10 weeks post-partum. Then they can be placed on a monthly broad-spectrum heartworm medication.

External Parasites:

Not only can several intestinal parasites be eliminated and/or prevented by the regular administration of broad-spectrum heartworm medications, some of these formulations can also control or prevent several of the most common external parasites of cats and dogs. Monthly administration of a single broad-spectrum heartworm medication with activity against both internal and external parasites, alone or in combination with an effective external parasiticide, can effectively manage fleas, ticks, lice, and several species of mites on cats.

Fleas

The most common external parasite of cats and dogs in North America is Ctenocephalides felis felis, the cat flea. Monthly applications of selamectin19 or imidacloprid/moxidectin20 can be used to effectively eliminate and prevent flea infestations. In addition the monthly administration of lufenuron (milbemycin-lufenuron) can effectively prevent development of flea infestions by inhibiting reproduction of hitchhiker fleas.21 The other broad-spectrum heartworm medications currently do not have activity against fleas but can be administered in conjunction with an effective flea product to achieve comprehensive control of fleas and heartworms.

Lice

Since most flea adulticides readily kill lice, lice are not commonly encountered in areas where fleas occur. Selamectin22 is highly effective aginst lice on both cats and dogs and imidacloprid23 in the imidacloprid/moxidectin formulation is also effective against lice. If the other broad-spectrum heartworm medications are used, an insecticide effective against lice, such as fipronil, imidacloprid, or permethrin (dogs only) must also be administered.

Mites

Notoedres cati produces face mange in cats and occurs more commonly along the gulf coast and southeastern United States. Sarcoptes scabiei is a highly pathogenic and zoonotic parasite of dogs. These mite infestations in dogs and cats can be managed by the administration of selamectin24,25 and imidacloprid/moxidectin are effective against scabies in dogs.26

Ear mites (Otodectes cynotis) are very common in cats and also dogs. The mites spend their entire life in the ears and are primarily transmitted between cats and dogs by direct contact. Ear mites can be treated and prevented by the monthly application of a broad-spectrum heartworm medication such as selamectin or the imidacloprid–moxidectin formulation.

Cheyletiellosis, or "walking dandruff," in cats and dogs in North America is caused by Cheyletiella spp. mites. The mites appear to be more common in temperate climates, where fleas are not as prevalent. This may be related to the widespread use in subtropical and tropical climates of certain flea products that also have activity against Cheyletiella spp. Cheyletiellosis can be treated and prevented by the monthly application of a broad-spectrum heartworm medication containing selamectin.

Conclusion

Historically, many veterinarians and pet owners attempted to administer broad-spectrum heartworm medications seasonally. Although seasonal prevention of heartworm and other parasites may at seem appropriate in many regions of North America, it is actually difficult to accomplish. Veterinarians must first attempt to estimate heartworm larvae development rates in mosquitoes so they can seasonally time the administration of heartworm preventives. Then they are faced with the difficulty if not impossibility of attempting to estimate the rate of flea development, tick questing patterns, mite and louse transmission, and development of infective roundworm eggs and hookworm larvae. Because of differences in the biologic requirements of each parasite, the specific transmission "seasons" vary among parasites. Changing climatic conditions from one year to the next can have marked effects on parasite "seasonality."

Studies have not been published comparing the effectiveness of year-round versus seasonally timed prevention programs, but it is this author's experience that determining when to start and stop seasonally timed applications of broad-spectrum parasite prevention programs is difficult. Considering the various and changing climatic epidemiologic factors and historic poor pet owner compliance it is understandable why the CAPC recommends year-round treatment with broad-spectrum heartworm medications (www.capcvet.org)

References

Browne LE, Carter TD, Levy JK, Snyder PS, Johnson CM. Pulmonary arterial disease in cats seropositive for Dirofilaria immitis but lacking adult heartworms in the heart and lungs. Am J Vet Res 66(9):1544-9,2005.

Nelson CT, McCall JW, Rubin SB, Buzhardt LF, Dorion DW, Graham W, Longhofer SL, Guerrero J, Robertson-Plouch C, Paul A; Executive Board of the American Heartworm Society. 2005 Guidelines for the diagnosis, prevention and management of heartworm (Dirofilaria immitis) infection in cats. Vet Parasitol 133(2-3):267-75, 2005.

Dryden MW, Payne PA. Preventing parasites in cats. Vet Ther 6(3):260-7, 2005.

Soulsby EJL. Helmiths, Arthropods and Protozoa of Domestic Animals 7th edition. Lea and Febiger, Philadelphia 1982, pp809.

Bowman DD, Lynn RC, Eberhard ML. Georgis' Parasitology for Veterinarians 8th Edition. Saunders, St. Louis MO. 2003.pp422.

Fukase T, In T, Chinone S, Akihama S, Itagaki H; Anthelmintic efficacy of milbemycin D against Toxocara cati and Ancylostoma tubaeforme in domestic cats. J Vet Med Sci 53(5):817-21, 1991.

McTier TL, Shanks DJ, Wren JA, Six RH, Bowman DD, McCall JW, Pengo G, Genchi C, Smothers CD, Rowan TG, Jernigan AD: Efficacy of selamectin against experimentally induced and naturally acquired infections of Toxocara cati and Ancylostoma tubaeforme in cats. Vet Parasitol 91(3-4):311-9, 2000.

Reinemeyer CR, Charles S: Evaluation of the efficacy of a combination of imidacloprid and moxidectin against immature Toxocara cati in cats. Parasitol Res 90 Suppl 3:S140-1, 2003.

Hellmann K, Knoppe T, Radeloff I, Heine J. The anthelmintic efficacy and the safety of a combination of imidacloprid and moxidectin spot-on in cats and dogs under field conditions in Europe. Parasitol Res 90 Suppl 3:S142-143, 2003.

Clark JN, Daurio CP, Plue RE, Wallace DH, Longhofer SL. Efficacy of ivermectin and pyrantel pamoate combined in a chewable formulation against heartworm, hookworm, and ascarid infections in dogs. Am J Vet Res 53(4):517-520, 1992.

Bowman DD, Parsons JC, Grieve RB, Hepler DI. Effects of milbemycin on adult Toxocara canis in dogs with experimentally induced infection. Am J Vet Res 49(11):1986-1989, 1988.

Schenker R, Cody R, Strehlau G, Alexander D, Junquera P. Comparative effects of milbemycin oxime-based and febantel-pyrantel embonate-based anthelmintic tablets on Toxocara canis egg shedding in naturally infected pups. Vet Parasitol 30;137(3-4):369-373, 2006.

Bowman DD, Barr SC, Hendrix CM, Lindsay DS: Gastro-intestinal Parasites of Cats (Last Updated: 24-Jan-2003). In Companion and Exotic Animal Parasitology, Bowman D.D. (Ed.). International Veterinary Information Service, Ithaca NY (www.ivis.org), 2003.

Humbert-Droz E, Buscher G, Cavalleri D, Junquera P: Efficacy of milbemycin oxime against fourth-stage larvae and adults of Ancylostoma tubaeforme in experimentally infected cats. Vet Rec 154(5):140-3, 2004.

Nolan TJ, Niamatali S, Bhopale V, Longhofer SL, Schad GA: Efficacy of a chewable formulation of ivermectin against a mixed infection of Ancylostoma braziliense and Ancylostoma tubaeforme in cats. Am J Vet Res 53(8):1411-3, 1992.

von Samson-Himmelstjerna G, Epe C, Schimmel A, Heine J. Larvicidal and persistent efficacy of an imidacloprid and moxidectin topical formulation against endoparasites in cats and dogs. Parasitol Res ;90 Suppl 3:S114-115, 2003.

Reinemeyer CR, Faulkner CT, Assadi-Rad AM, Burr JH, Patton S. Comparison of the efficacies of three heartworm preventives against experimentally induced infections with Ancylostoma caninum and Toxocara canis in pups. J Am Vet Med Assoc 206(11):1710-1715, 1995.

Bowman DD, Johnson RC, Hepler DI. Effects of milbemycin oxime on adult hookworms in dogs with naturally acquired infections. Am J Vet Res 51(3):487-490, 1990.

Dryden MW, Burkindine S, Lewis T, Houdeshell L, Rodriquez I, Hack R: Efficacy of selamectin in controlling natural flea infestations on pets and in private residences in comparison with imidacloprid and fipronil In proceedings of the Am Assoc of Vet Parasitol Ann Meeting. July 14 – 15, 2001 Boston MA. P34.

Arther RG, Bowmann DD, McCall JW, Hansen O, Young DR: Feline Advantage Heart (imidacloprid and moxidectin) topical solution as monthly treatment for prevention of heartworm infection (Dirofilaria immitis) and control of fleas (Ctenocephalides felis) on cats. Parasitol Res. 90 Suppl 3:S137-9, 2003.

Dryden M, Brown H, Buck S, Schwahn R, Sloan T, Summers S. Effective Long Term Protection Against Flea Infestations Vet. Med. June. 16 – 18, 1998.

Shanks DJ, Gautier P, McTier TL, Evans NA, Pengo G, Rowan TG. Efficacy of selamectin against biting lice on dogs and cats. Vet Rec 152(8):234-237, 2003.

Hanssen I, Mencke N, Asskildt H, Ewald-Hamm D, Dorn H. Field study on the insecticidal efficacy of Advantage against natural infestations of dogs with lice. Parasitol Res 85(4):347-348, 1999.

Six RH, Clemence RG, Thomas CA, Behan S, Boy MG, Watson P, Benchaoui HA, Clements PJ, Rowan TG, Jernigan AD. Efficacy and safety of selamectin against Sarcoptes scabiei on dogs and Otodectes cynotis on dogs and cats presented as veterinary patients. Vet Parasitol 91(3-4):291-309, 2000.

Itoh N, Muraoka N, Aoki M, Itagaki T: Treatment of Notoedres cati infestation in cats with selamectin. Vet Rec 154(13):409, 2004.

Fourie LJ, Heine J, Horak IG. The efficacy of an imidacloprid/moxidectin combination against naturally acquired Sarcoptes scabiei infestations on dogs. Aust Vet J 84(1-2):17-21, 2006.