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Nematodes

A nematode is a roundworm. Infection with any of the roundworms represents a significant proportion of the diseases of animals. Common nematodes include Ancylostoma (hookworm), Ascaris (ascarid), Capillaria, Dictyocaulus (lungworm), Dioctophyme renale (giant kidney worm), Dirofilaria, Habronema, Haemonchus (blood-sucking nematode), Metastrongylus (lungworm), Muellerius (lungworm), Onchocerca (skin worm), Ostertagia (brown stomach worms), Oxyuris (intestinal worm), Parafilaria, Parascaris, Protostrongylus (hairlike lungworm), Rhabditis, Skrjabinema, Spirocerca, Strongyloides (threadworm), Strongylus (redworm), Syngamus, Thelazia (eyeworm), Trichuris (whipworm), Toxocara (zoonotic roundworm), Trichinella (trichina worm), and Trichostrongylus.

Ascarids are particularly injurious to puppies and kittens. The commonest signs are unthriftiness, digestive disturbances, bloated and pot bellied appearance. Puppies with heavy prenatal infection with T. canis suffer from diarrhea, have frequent vomiting and occasionally die from intestinal obstruction or perforation. Anemia and nervous disturbances are observed, although no satisfactory explanation for this manifestation exists. Migration through the lungs may trigger pneumonia which is complicated by secondary infections.

Human infection with roundworms of the genus Toxocara causes toxocariasis which occurs mostly in children. the infection is caused mainly by T. canis, and occasionally by T. cati and T. leonina. Ocular larva migrans causes granulomatous inflammation, which may result in a variety of other clinical symptoms including keratitis, iridocyclitis, chronic endophthalmitis and detached retina.

Three species of ascarids are commonly found in pet animals: Toxocara canis (infecting dogs), Toxocara cati (infecting cats), and Toxascaris leonina (infecting dogs and cats). The adult females of this worm may reach a length of 18 cm for T. canis and 6 cm for the other two species. Transmission in all species may be direct by ingesting eggs or transuterine by larvae from the infected females. The life cycle of the ascarids comprises eggs produced by the female and five larval stages that develop in various organs and the intestine of the host. A female ascarids may lay about 200,000 eggs per day, which are excreted in the feces of the host and shed into the environment. An infective larval stage develops within the eggs on the ground in 3-7 days. The eggs which posses a thick protective shell may survive in the environment for more than one year. Rodents and some invertebrates are susceptible to Toxocara infections and second stage larvae that develop in these hosts may infect dogs and cats predating on infected mice or cockroaches.

After ingestion by the host, the eggs hatch to release the second stage larva. The larvae migrate from the intestine through the liver to the lungs and then through the trachea and the oesophagus to the intestine. Prenatal infection by these nematodes is extremely common in Toxocara canis infection. However, infection occurs also by ingestion of eggs by adult dogs as well as by young puppies. After the initial infection larvae are able to remain dormant in the female dog in various tissues for nearly all her lifetime and she may transmit infection to several litters. Coprologic examination of bitches infected with tissue larvae may show negative results, however, they are still capable of transmitting infection to their progeny. Activation of the larvae in the mother, followed by migration to the fetus, occurs usually around the 42nd day of pregnancy and third stage larvae (1.0 mm of length) are found in the lungs of the fetuses before birth. A molt to the fourth larval stage (5-7 mm) occurs in puppies during the first week after birth when they are found in the intestine. Throughout the second and third week after birth a fifth larva stage grow rapidly to become an adult worm.

FDA approved drugs for the treatment of infections with roundworm include:

  • Canine Worm Caps. (K.C. Pharmacal, Inc.)
  • Pulvex Worm Caps. (Virbac AH, Inc.)
  • N-Butyl Chloride Canine Worming Caps. (IMPAX Laboratories)
  • Diethylcarbamazine Citrate Tab. (Lloyd, Inc.)
  • Nemacide Oral Syrup (Boehringer Ingelheim Vetmedica, Inc.)
  • Dirocide Tablets (Fort Dodge Animal Health, Division of Wyeth Holdings Corp., a wholly owned subsidiary of Pfizer, Inc.)
  • Difolin Capsules (Fort Dodge Animal Health, Division of Wyeth, a wholly owned subsidiary of Pfizer, Inc.)
  • NBC Kaps Wormer (Pfizer, Inc.)
  • Difil Syrup & Tab. (Evsco Pharmaceuticals, An Affiliate of IGI, Inc.)
  • Thenatol PW Tablets (Intervet, Inc.)
  • Dog Wormer Tablets (Farnam Companies, Inc.)
  • Worming Capsules For Puppies, Small Dogs And Cats (Pegasus Laboratories, Inc.)
  • L.K. Worming Capsules For Dogs (Pegasus Laboratories, Inc.)
  • Tri-Plex Worm Capsules (Intervet, Inc.)
  • Pulvex Multipurpose Worm Caps (Virbac AH, Inc.)
  • Trivermicide Worm Capsules (Happy Jack, Inc.)
  • Filaribits® Chewable Tablets (Pfizer, Inc.)
  • Worm Capsules (Farnam Companies, Inc.)
  • Carbam® Tablets (Cross Vetpharm Group Ltd.)
  • DEC Tabs 400 mg (Wendt Laboratories, Inc.)
  • Dichlorophene & Toluene Caps. (Texas Vitamin Co.)
  • Filban Chewable Wafers (Intervet, Inc.)
  • THR Worm Capsules (Natchez Animal Supply Co.)
  • Diethylcarbamazine Citrate Cap. (R.P. Scherer North America)
  • Filban Tablets (Intervet, Inc.)
  • D & T Worm Capsules (Boehringer Ingelheim Vetmedica, Inc.)
  • Pet-Dec (Pfizer, Inc.)
  • Vercom Paste Anthelmintic (Bayer Healthcare LLC, Animal Health Division)
  • Filaribits® Plus Chewable Tablets (Pfizer, Inc.)
  • Dichlorophene / Toluene (IMPAX Laboratories)
  • Adams™, Dog Wormer Chewable Tablets, D-Worm™ (Farnam Companies, Inc.)
  • Elite Dog & Cat Wormer (RSR Laboratories, Inc.)
  • Rintal® Tabs Anthelmintic Tablets (Bayer Healthcare LLC, Animal Health Division)
  • Drontal® Plus Broad Spectrum Anthelmintic Tablets, Drontal® Plus Taste Tabs®, Drontal® Plus Tablets (Bayer Healthcare LLC, Animal Health Division)
  • Wormexx™ Chewable Tablets (Virbac AH, Inc.)
  • Vermiplex (Intervet, Inc.)
  • Happy Jack Worm Capsules (Happy Jack, Inc.)
  • Anaplex Caps Canine and Feline Wormer Caps (Boehringer Ingelheim Vetmedica, Inc.)
References
  1. Recent development in the Control of Ectoparasites and Endoparasites of Dogs and Cats with Selamectin, E. Pipano
  2. Essentials of Veterinary Parasitology. Hany M. Elsheikha, Hany M. Elsheikha and Naveed Ahmed Khan (editors)
  3. Animal Drugs @ FDA
  4. Neglected Infections of Poverty in the United States of America. Peter J. Hotez

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