Chapter 5: Important Canine Diseases and How to Treat Them 6 CE Hours By: Staff Writer Learning objectives Upon completion of this course, the learner will be able to: and ability to overcome the disease. Table 1 presents an overview of Explain the interaction between host and pathogen. the canine diseases most frequently found during visits to standard Identify canines’ defense mechanisms. veterinary clinics and some of the medications available for their Describe pathogens’ weaknesses and strengths. treatment that are discussed in this course. A comprehensive Identify medication used to treat these diseases. bibliography is provided at the end of this discourse, as well. Diseases In this course we will examine some of the more important diseases preventable by vaccination such as parvo, corona, hepatitis, rabies, affecting dogs. We will review how the disease interacts with dogs’ parainfluenza viruses, Lyme disease, leptospirosis, and kennel cough bodies and what how to strengthen and fortify a dog’s resistance are not included in this course. TABLE 1: OVERVIEW OF MAJOR CANINE DISEASES, SOME TREATMENT OPTIONS DISEASE MEDICATIONS Heartworm Macrolides (macrocyclic lactones), diethylcarbamazine. Flea infestation Advantage II, K9Advantix II, BioSpot, Frontline, Frontline Plus Certifect, FiproGuard. Worm infestation Dog Worms 3, Nemex 2, Pro Wormer 2, Safe-Guard, D-Worm. Joint pain Rimadyl, Tramadol, Metacam, Cosequin DS, Etodolac, Aspirin. Ear infection Zymox Otic, Revolution, Panolog Ointment, Animax. Eye disease Terramycin, Vetericyn, Opticlear. Skin disease Animax, Fungisan, Betadine, Vetericyn, Ketochlor, Panolog, Zymox. Bladder infection Amoxicillin, Zeniquin, Baytril, Cephalosporine, Tetracycline. High blood pressure Amlodipine, Enalapril, Inderal, Tenormin. Giardiasis Ornidazole, Tinidazole, Metronidazole, Nitazoxanide, Albendazole. Heartworm (Dirofilariasis) CAUSE: Dirofilaria Radiography of the thorax will confirm the diagnosis and provide an immitis, a nematode, is indication of the extent and severity of the nematode burden. carried by mosquitoes The disease process goes from: (culex, aedes, ● Stage 1: Early infestation, often asymptomatic with the occasional anopheles, and others) cough. The physical examination, and even radiography, may find as intermediate hosts. nothing. Wild animals (foxes, ● Stage 2: In a more advanced stage, symptoms include dyspnea, wolves, coyotes, some coughing, slowing down, and disinclination to exercise. raccoons, seals, or sea Radiography will show some enlargement of the pulmonary artery lions) may serve as and interstitial lesions. There will be minor anemia and evidence reservoir in of protein in the urine. geographical regions ● Stage 3: Frequent coughing, unwillingness to move and exercise, conducive to the multiplication of mosquitoes. After entering the weight loss, increasing enlargement of the pulmonary artery, often mosquito and only with outside temperatures remaining above 13.9°C affecting the right ventricle of the heart and arteriolar infiltration, (57°F), the microfilaridae develop through Larval Stages 1 and 2 and and pronounced anemia and proteinuria. are passed on as Larval Stage 3 to the next blood donor, usually the ● Stage 4: There may be hundreds of worms invading the heart, dog. In the dog’s subcutaneous and sub-muscular tissues, the worm lungs, and caval veins, obstructing the vasculatory system, which develops to its mature stage (Larval Stage 5) and enters the circulatory results in pronounced dyspnea, tachycardia, anemia, and dark system, ending up in the pulmonary artery and, usually, the right heart hemoglobinuria. The dog may be close to collapse and death. ventricle. The mature male dirofilariae grow to about 6 inches while In a dog without obvious signs of the disease, the presence of a the female may reach more than 1 foot. They may reside in the heart specific antigen will confirm the diagnosis using the Enzyme- and the pulmonary artery for years. Linked ImmunoSorbent Assay (ELISA) procedure. ELISA test kits Diagnosis: Clinical symptoms of the disease include coughing, are available from a variety of manufacturers. They can also be hemoptysis, and epistaxis, breathing difficulties, lethargy and produced in-house. In short, they consist of: unwillingness to move, unthriftiness, cyanosis, fainting, and ascites. veterinarians.elitecme.com Page 42 1. An antibody specific to the antigen that is being looking for, the result of prior preventive treatment and not necessarily indicate fixed onto a surface; absence of active infestation. 2. The antigen to confirm the presence of the antibody (positive Prevention: Prevention of infestation is, obviously, preferable to control), the test sample, and a diluent sample (negative treatment of the established disease. Reducing exposure to mosquito control); bites is a positive step. Prevention is possible by regular application of 3. Diluent to wash off controls and unadhered test sample; macrocyclic lactones, such as Ivermectin, Milbemycin, Moxidectin, 4. Antigen-specific antibody, which has been combined with an and Selamectin (Table 2), followed by appropriate veterinary check- enzyme to indicate the presence of an antigen attached to the ups and serology. Macrolides, derived from Streptomyces Sp., stop known antibody; the development of larvae early after infection, and prevent the further 5. Enzyme substrate to indicate the presence of the enzyme development of microfilariae to the mature female thus breaking the by changing its color (only present when there is a positive nematode’s replication cycle. Preventive treatment should commence antigen residue on the test sample). early in the life of the pup, about 6 to 8 weeks of age, and ideally There are many varieties of this testing procedure in many different continue monthly, year-round. At the very least, it should start 1 month test kits, too many to be discussed in this context. One can expect before the mosquito season and continue until at least 1 month after to detect the antigen with at least three developed female worms, the end of the mosquito threat. In the latter case, and when there was about 6 to 7 months after onset of the infestation. However, if there a chance of an earlier mosquito contact, the animal should be tested are only immature worms or males, there will be no antigen-positive for the presence of dirofilaria antigen or the parasite itself. This is results. In the blood of microfilaremic dogs, one might find circulating important because of the possibility of allergic shock following the microfilariae. To improve chances of finding them, the blood sample destruction of significant numbers of the nematode and its larvae can be centrifuged and the sediment examined microscopically, or subsequent to treatment, thus presenting the host suddenly with large after lysing the blood cell population, the circulating larvae can be amounts of allergenic foreign protein. collected on a filter. Not finding any, on the other hand, may only be TABLE 2: MACROLIDES FOR HEARTWORM PREVENTION BRAND AGENT DOSAGE EFFECTIVENESS Heartgard Ivermectin 6-12 µg/kg/mth/po Heartworm. HeartgardPlus Ivermectin/Pyrantel 6 µg/5 mg per kg/mth/po Heartworm, roundworm, hookworm. Interceptor* Milbemycin oxime 0.5-1 mg/kg/mth/po Heartworm, round-, hook-, whipworm. Sentinel* Milbem. ox./ Lufenuron 0.5-1 mg/kg/mth/po Heartworm, fleas, round-, hook-, whipworm. ProHeart 6* Moxidectin 0.17 mg/kg/6mths/im Heartworm, hookworm. Advantage Multi Imidacloprid/Moxidectin 20 mg/5mg/kg/mth/top Heartworm, fleas, round-, hook-, whipworm. Revolution Selamectin 6-12 mg/kg/mth/top Heartworm, fleas, ticks, mites. * manufacturer suspended production Action of preventatives: Macrolides encompass biologicals with active ingredient of ivermectin, abamectin, doramectin, eprinomectin, macrocyclic lactone rings. They are derived from Streptomyces selamectin, and others. Even low doses are highly effective Sp., an actinobacterium. This group of agents includes, along with against immature dirofilaria both in preventive and treating modes. highly effective antinematodal and insecticidal drugs, antibiotics, Avermectins do not kill the adult worm, although extended prophylaxis antifungals, gastroprokinetics (affecting gastrointestinal motility), and with this drug will clear up the infestation eventually. Prophylactic immunosuppressants. Avermectins and milbemycins, in particular, potency persists for more than a month, justifying the recommended are mentioned here as the most effective means of fighting dirofilaria monthly dosage. nematodes. Avermectin, isolated from Streptomyces avermitilis, is the TABLE 3: HEARTWORM DEVELOPMENTAL PROGRESS Dirofilaria Stages: L1 L2 L3 (infective) L4 Adult Mosquito Host: Mosquito Mosquito Mosquito (labia) - - Canine Host: - - Dog (skin) Abdomen-Thorax Pulmonary/Heart Duration of Growth: 4 wks (2 if amb.T° >27°C) 3-12 days 50-70 days 70-120 days Duration of Existence: 7-9 months 3-5-10 years Treatment: Mosquito Control Macrolides Melarsomine Dosage can be oral, parenteral, or topical. Spreading throughout pH, cell migration, cell proliferation and differentiation, cell volume, the body via any of those routes, it will be concentrated quickly in epithelial fluid secretion and solute transport, smooth muscle action, the fatty connective tissue of skin, gastrointestinal tract, and lungs. and neuro-excitation. Glutamate-gated chloride channels do not Oral dosage can be improved by reducing food intake at the time of exist in mammals, making the activity of this drug