12.1 Common Parasites of Domestic Animals

Domestic animals face a variety of parasitic threats, from intestinal worms to skin-burrowing mites. These parasites can cause serious health issues, impacting animal welfare and productivity. Understanding common parasites is crucial for effective prevention and treatment.

Veterinarians must be familiar with parasite life cycles, transmission routes, and clinical signs to diagnose and treat infections accurately. From fecal tests to skin scrapings, various diagnostic methods help identify specific parasites. Treatment options range from broad-spectrum anthelmintics to targeted antiparasitic drugs.

Parasitic Infections in Domestic Animals

Common Endoparasites in Dogs and Cats

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• Roundworms (Toxocara canis, Toxocara cati) are prevalent intestinal parasites that can cause pot-bellied appearance, diarrhea, vomiting, and poor growth in puppies and kittens
• Hookworms (Ancylostoma caninum, Ancylostoma tubaeforme) are blood-sucking parasites that can lead to anemia, diarrhea, and weight loss
  • Cutaneous larval migrans may occur in humans who come into contact with infected soil or sand
• Whipworms (Trichuris vulpis) inhabit the cecum and colon, causing inflammation, diarrhea, and weight loss
• Tapeworms (Dipylidium caninum, Taenia spp.) are segmented parasites that can cause abdominal discomfort and visible proglottids in feces

Ectoparasites Frequently Affecting Dogs and Cats

• Fleas (Ctenocephalides felis) are common external parasites that cause itching, hair loss, and flea allergy dermatitis
  • Heavy infestations can lead to anemia, especially in young or small animals
• Ticks (Rhipicephalus sanguineus, Ixodes spp.) are blood-sucking parasites that can transmit various diseases, such as Lyme disease, ehrlichiosis, and anaplasmosis
• Mites, including Sarcoptes scabiei (sarcoptic mange), Otodectes cynotis (ear mites), and Demodex canis (demodectic mange), can cause skin irritation, hair loss, and secondary bacterial infections

Parasitic Infections in Livestock

• Gastrointestinal nematodes, such as Haemonchus contortus, Ostertagia ostertagi, and Trichostrongylus spp., are common in cattle, sheep, and goats, causing anemia, diarrhea, and reduced production
• Fasciola hepatica (liver fluke) is a trematode that affects the liver and bile ducts of ruminants, leading to fascioliasis, which can cause weight loss, anemia, and sudden death
• Eimeria spp. are protozoan parasites that cause coccidiosis, an intestinal disease characterized by diarrhea, dehydration, and weight loss in young animals
  • Coccidiosis is particularly problematic in intensive rearing conditions, such as poultry farms and cattle feedlots

Life Cycles and Transmission of Key Parasites

Direct Life Cycles

• Roundworms (Toxocara spp.) have a direct life cycle, with eggs shed in feces and becoming infective in the environment
  • Transmission occurs through ingestion of infective eggs or transplacental and transmammary routes in dogs
• Hookworms (Ancylostoma spp.) also have a direct life cycle, with eggs shed in feces and larvae developing in the environment
  • Transmission occurs through percutaneous penetration of infective larvae, ingestion of larvae, or transmammary route in dogs
• Haemonchus contortus, a gastrointestinal nematode of ruminants, has a direct life cycle, with eggs shed in feces and infective larvae developing in the environment
  • Transmission occurs through ingestion of infective larvae on pasture

Indirect Life Cycles

• Dipylidium caninum, a common tapeworm in dogs and cats, has an indirect life cycle involving flea intermediate hosts
  • Pets become infected by ingesting infected fleas during grooming
• Toxoplasma gondii, a protozoan parasite, has a complex life cycle involving felines as definitive hosts and various intermediate hosts
  • Transmission occurs through ingestion of oocysts from the environment or tissue cysts in infected prey or meat
  • Humans can become infected by ingesting oocysts from contaminated soil or water, or by consuming undercooked meat containing tissue cysts

Clinical Signs and Pathology of Parasitic Diseases

Gastrointestinal Parasites

• Roundworm infections in puppies and kittens can cause pot-bellied appearance, diarrhea, vomiting, and poor growth
  • Heavy infections may lead to intestinal obstruction and even rupture
• Hookworm infections can result in anemia, diarrhea, and weight loss in dogs and cats
  • Cutaneous larval migrans, characterized by serpentine tracks in the skin, may occur in humans who come into contact with infected soil or sand
• Coccidiosis, caused by Eimeria spp., can cause diarrhea, dehydration, and weight loss in young animals, particularly in intensive rearing conditions
  • Severe infections can lead to mortality, especially in young or immunocompromised animals

Ectoparasites and Skin Diseases

• Sarcoptic mange, caused by Sarcoptes scabiei mites, leads to intense pruritus, alopecia, and crusting of the skin in dogs
  • The mites burrow into the skin, causing inflammation and secondary bacterial infections
• Demodicosis, caused by Demodex canis mites, can result in hair loss, skin redness, and scaling
  • Generalized demodicosis can be a serious condition, particularly in young or immunocompromised dogs
• Flea infestations can cause itching, hair loss, and flea allergy dermatitis in dogs and cats
  • Heavy infestations can lead to anemia, especially in young or small animals

Systemic Parasitic Diseases

• Haemonchosis in ruminants, caused by Haemonchus contortus, results in anemia, hypoproteinemia, submandibular edema (bottle jaw), and weight loss
  • Heavy infections can lead to death, particularly in young or stressed animals
• Fascioliasis, caused by Fasciola hepatica, can lead to liver damage, weight loss, anemia, and sudden death in ruminants
  • Chronic infections may cause fibrosis and calcification of the bile ducts

Diagnosis and Treatment of Parasitic Infections

Diagnostic Methods

• Fecal flotation is a common diagnostic method for detecting helminth eggs and protozoan oocysts in fecal samples
  • Different flotation solutions, such as sodium nitrate or zinc sulfate, can be used depending on the parasite of interest
• Fecal sedimentation techniques, such as the Benedect's sedimentation method, are used for diagnosing trematode infections like Fasciola hepatica
  • These techniques concentrate heavier parasite eggs that do not float well in standard flotation solutions
• Skin scrapings and microscopic examination are used to diagnose ectoparasitic infestations, such as sarcoptic mange and demodicosis
  • The scrapings are examined under a microscope to identify the presence of mites or their eggs

Treatment Options

• Anthelmintics are used to treat helminth infections in domestic animals
  • Macrocyclic lactones (ivermectin, moxidectin) are effective against a wide range of nematodes and some ectoparasites
  • Benzimidazoles (fenbendazole, albendazole) are used to treat nematode and some cestode infections
  • Tetrahydropyrimidines (pyrantel) are effective against roundworms and hookworms
• Praziquantel is the drug of choice for treating tapeworm infections in dogs and cats
  • It is often combined with other anthelmintics in broad-spectrum deworming products
• Anticoccidial drugs, such as sulfadimethoxine and toltrazuril, are used to control coccidiosis in livestock and poultry
  • These drugs inhibit the development of the parasite, reducing the severity of the disease
• Insecticides and acaricides are used to control ectoparasitic infestations in companion animals
  • Fipronil, selamectin, and fluralaner are examples of topical or oral products that can be used to treat and prevent flea and tick infestations
  • Lime sulfur dips and ivermectin are often used to treat sarcoptic mange and demodicosis in dogs