Canine and Feline Ascarids PDF

CLINICAL PATHOLOGY I – Lecture Ascarids of Dogs & Cats I. General Ascarid Info A. Among the largest and most familiar of nematode parasites B. Life cycle is direct No intermediate host involved, BUT......

CLINICAL PATHOLOGY I – Lecture Ascarids of Dogs & Cats I. General Ascarid Info A. Among the largest and most familiar of nematode parasites B. Life cycle is direct No intermediate host involved, BUT... Some may be transferred by paratenic host (PH) = indirect transmission C. May or may not migrate inside body of the host D. Generally host-specific E. Adult worm located in small intestine of host II. Ascarid Ova A. Ova passed in feces of definitive host (DH) B. Typically require 2 to 4 weeks for ova to become “infective”; i.e., larvae have developed inside ova (Toxascaris leonina only 1 week) C. Infective ova are very resistant to the environment and can live in soil for years D. Infective ova ingested by new DH (or by a PH who is subsequently ingested by DH) III. Transmission of Companion Animal Ascarids Transmissions occur between hosts A. Oral Transmission 1. Ova produced by adult female ascarid in small intestine of DH 2. Ova pass with feces of DH 3. Next definitive host (DH) ingests infective ova 4. Ova hatch in stomach or small intestine 5. Larvae may migrate through the body* 6. Depending on age and species of host, adults may lodge in small intestine of DH, mature and begin to reproduce 7. Cycle begins again * This varies with the age and species of the DH B. Transplacental Transmission* 1. Larvae (L2) that have hatched in the stomach of the pregnant bitch or are encysted in tissues of pregnant bitch move to uterus and cross placenta into fetal liver (at approximately day 42 of gestation) 2. Puppy is born infested 3. Ultimately, adult worms lodge in small intestine and pup begins to pass ova in feces at 21 days of age. *Primary route of transmission in puppies. The feline ascarid (T. cati) does not undergo this type of transmission 8/13/2023 1  C. Transmammary Transmission** 1. Larvae (L2) that have hatched in the stomach of the bitch or are encysted in bitch’s tissues (and maybe in queen†) migrate to mammary gland and are passed to young via milk 2. Ultimately, adult worms lodge in small intestine of puppy (and maybe in the kitten†) who subsequently pass ova in feces **This is a less common route of transmission of T. canis than the transplacental route to puppies D. Paratenic Host Transmission*** 1. Infective ova are ingested by something other than the DH; e.g., rodents, rabbits, earthworms, birds, flies, PEOPLE 2. Larvae arrest (encyst) in muscle or other tissue of PH 3. Larvae complete life cycle only if PH is eaten by DH ***This route of transmission may be more important in predatory hosts such as the fox or coyote than in pet dogs and cats IV. Migration of Ascarid Larvae Migrations occur within a host A. Mucosal Migration† 1. Larvae burrow into mucosa of the small intestine 2. Their development continues until... 3. They emerge back into lumen of small intestine and moult to adult stage † Required for final stage of ascarid maturation. Patent infestation does not develop without MM B. Tracheal Migration* 1. After ingestion of infective ova (or via transplacental transmission = already in liver), larvae migrate from small intestine to liver 2. Migrate within hours of ingestion, but can tunnel around liver for days (creating hepatic lesions) 3. Enter caudal vena cava and are carried to heart 4. From heart, larvae are carried by pulmonary artery to lungs, where they burrow out of capillaries and into alveoli 5. From lungs, larvae migrate to trachea, are coughed up and swallowed, and return to small intestine where, following a mucosal migration, they develop into adults 6. Adults lay eggs that are passed in feces – takes approximately 4 or 8 weeks post-infestation for eggs to appear in feces. (Pre-patent period: T. canis = 4 weeks; T. cati = 8 weeks) *This migration pattern occurs most commonly in young puppies (< 3 months of age), young kittens, and adult cats C. Somatic Migration** 1. When older puppies (> 3 months of age) and adult dogs ingest infective ova, larvae begin their migration just like a tracheal migration 2. However, instead of breaking out of alveoli in lung, some larvae remain in circulatory system 3. These larvae travel through bloodstream to various organs and tissues (mostly muscle and kidneys) 8/13/2023 2  4. Larvae encyst in tissues 5. Larval development is arrested and can remain for years in host tissue 6. Later in the intact female’s life, larvae are reactivated during late pregnancy and migrate To uterus and through placenta to fetal liver, resulting in transplacental transmission to puppies To mammary glands and into milk resulting in transmammary transmission to puppies (and possibly kittens) To the small intestine of the dam and set up a new, patent infestation **This migration pattern occurs most commonly in older puppies, adult dogs, and adult cats V. The Canine Ascarid: Toxocara canis A. General Information 1. DH = Dog 2. Ova of T. canis are slightly larger than T. cati Not possible to determine on fecal exam Must know species of the feces 3. Zoonotic 4. Ovum requires 2 – 4 weeks to become infective 5. Patent infestations most common in young puppies; i.e., typically those < 5 weeks of age, but may be found in older puppies and adult dogs; however... 6. Adult dogs and older puppies are more likely have larvae encyst in their tissues 7. Transplacental transmission is most important route of transmission for infestation of pups 8. Prepatent period: 2 to 4 weeks 2 weeks if acquired via paratenic host (PH) or transmammary transmission 4 weeks if infective ova are ingested or if contracted via transplacental transmission (BUT, if acquired prenatally, may begin shedding ova at a mere 21 days of age). B. Types of Transmission 1. Oral: Infective ova ingested by next DH 2. Transplacental*: Larvae migrate through placenta to fetal liver 3. Transmammary: Larvae passed to puppy via milk 4. Paratenic host: DH eats infested PH *Most important route of transmission in puppies C. Tracheal Migration* 1. Larvae, from ingested ova, migrate from small intestine, by way of portal vein, to liver (OR are already in liver via transplacental transmission) 2. Larvae travel from liver to lungs via circulatory system 3. Larvae break out of pulmonary capillary into alveoli 4. Larvae migrate and/or are coughed up trachea 5. Larvae are swallowed back to small intestine where, following a mucosal migration, they mature into adult ascarids *Occurs primarily in young puppies (< 3 months of age) 8/13/2023 3  D. Somatic Migration** 1. Begins like tracheal migration, but instead of breaking out of alveoli..... 2. Larvae remain in circulatory system and travel to tissues other than lungs (generally muscle and/or kidney) 3. Larvae encyst and development is arrested 4. Encysted larvae are reactivated in bitch during late pregnancy 5. Larvae are passed to pups via transplacental or transmammary transmission, AND these newly stimulated larvae can also set up a patent infestation in the bitch **Occurs primarily in older puppies (> 3 months of age) and adult dogs VI. The Feline Ascarid: Toxocara cati A. General Information 1. DH = Cats 2. Look nearly identical to T. canis 3. Zoonotic 4. Ovum takes 2 – 4 weeks to become infective 5. Prenatal infestation via placenta does NOT occur 6. Neonatal infestation occurs via transmammary transmission and is very important route of infestation in young kittens 7. Probability of tracheal migration remains high throughout a cat’s life 8. Prepatent period = 8 weeks B. Types of transmission 1. Oral 2. Transmammary* 3. Paratenic host *Most important route of transmission in kittens. C. Migrations 1. Mucosal: Larvae burrow into mucosa of small intestine to mature into adults (final stage of maturation; results in patent infestation) 2. Tracheal: Occurs in both kittens and adult cats Results in patent infestation (following mucosal migration) 3. Somatic: Occurs primarily in adult cats Results in encysted larvae Provides source of larvae for transmammary transmission 8/13/2023 4 VII. The Dog and Cat Ascarid: Toxascaris leonina A. General Information 1. Affects both dogs and cats 2. Ovum becomes infective in 1 week 3. Oral and paratenic host transmission 4. No transplacental or transmammary transmission 5. No somatic or tracheal migration 6. Mucosal migration only: Larvae migrate into intestinal mucosa of host to mature 7. More likely (than T. canis or T. cati) to be found in adult animals (especially dogs) 8. Prepatent period = 8 weeks in dogs; 10 weeks in cats 9. Not zoonotic VIII. Clinical Signs of Ascarids A. In Puppies 1. Can vary from subclinical to death in heavily infested newborns Intussusception of GI tract Obstruction of GI tract Rupture of GI tract 2. Common clinical signs include “unthrifty” appearance: Pot-bellied dull hair coat diarrhea or constipation Cough small size poor resistance to other diseases decreased stamina abdominal discomfort or “colic” may observe adult worms in feces B. In Kittens 1. Often subclinical, may appear “unthrifty” if heavily parasitized: Coughing Vomiting diarrhea or constipation pot belly appearance IX.Diagnosis A. Adult worms might be seen in vomitus and stool, BUT.... B. Must confirm with a fecal examination – if beyond prepatent period, perform a microscopic fecal exam. 1. Other parasites could also be present 2. Is it zoonotic (T. canis or T. cati) or not (Toxascaris leonina) C. Ova observed and identified on a fecal float 8/13/2023 5  X.Zoonotic Ascarids A. Public health significance 1. T. canis, T. cati, Baylisascaris procyonis and Ascaris suum have zoonotic potential 2. Dogs can develop a patent infestation of Baylisascaris procyonis and subsequently pass ova in their feces 3. Can be transmitted to people via ingestion of infective ova 4. Toxascaris leonina DOES NOT infest people This is why it is important to know the difference between the ova when performing a microscopic exam B. Clinical Signs in Humans: Visceral and Ocular Larva Migrans 1. Usually occur in young children (toddlers ingesting contaminated dirt) 2. Infective ova hatch, larvae migrate through tissues Liver, lungs, CNS = Visceral Larva Migrans (VLM) Eyes = Ocular Larva Migrans (OLM) 3. Larvae become walled off in various tissues (human becomes a paratenic host – parasite does not complete life cycle) C. Visceral Larva Migrans 1. Clinical signs are due to damage from migrating larvae Liver: Hepatomegaly Lungs: Pneumonitis Kidneys: Renal failure Brain: Brain damage; neurological signs D. Ocular Larva Migrans Eyes: Blindness It is our responsibility to educate our clients re: prevention, but it is their responsibility to seek out proper medical advice from their M.D. XI. Treatment of Ascarids A. Drugs that kill adult ascarids 1. Dogs and cats Piperazine: Over-the-counter (OTC); many different brand names; 52% to 100% effective (PO) Pyrantel pamoate: 95% effective; yellow, banana-flavored liquid; easy to administer (PO) Fenbendazole: 99% effective; most commonly used; powder and liquid available (PO) Milbemycin oxime (PO) Moxidectin (Topical) 2. Also effective in cats Selamectin (Topical) Emodepside (Topical) 8/13/2023 6  B. Drug that kill larval ascarids 1. Fenbendazole Most commonly used drug to kill larval ascarids Must treat every two weeks for several treatments Safe for use in lactating and pregnant bitches C. Treatment Regimen 1. Pregnant bitch: “Off-label” use Ivermectin (high doses) 2 – 4 times during pregnancy Fenbendazole SID from  Day 40 of gestation through  Day 3 after whelping 2. Puppies Pyrantel pamoate at 2, 4, 6, and 8 weeks of age; then begin monthly heartworm prevention with efficacy against T. canis Fenbendazole  SID x 3 days  Repeat every 2 weeks for several rounds of treatment 3. Kittens Pyrantel pamoate at 2 weeks of age (for hookworms), again at 6 weeks of age for (ascarids and hookworms); at 8 weeks of age, begin monthly heartworm prevention with efficacy against T. cati Fenbendazole: “Off-label” use  SID x 5 days  Repeat every 2 weeks for several rounds of treatment XI. Care of the Infested Puppy or Kitten 1. Strict hygiene is necessary to prevent reinfestation 2. Warm, dry housing 3. High quality balanced diet 4. Supplemental vitamins and minerals XII. Environmental Control A. Ascarid ova are very difficult to kill; can only be destroyed via 1. Steam sterilization 2. Complete removal of topsoil 3. Prescribed burns 4. Entombment in concrete or asphalt B. Most effective control is systematic removal of all fecal material 8/13/2023 7