Internal Parasites

Definitions Definitive host Intermediate host Reservoir host Harbors the adult parasite Intermediate host Harbors the immature parasite Reservoir host Harbors a parasite but is not affected by the parasite The adult form of a parasite is the sexually mature form. The immature parasite is asexual.

Educating Clients Parastic life cycles Client education Clues regarding risks Clues to prevention Clues to treatment interval protocols Client education Accuracy in word choices Well-informed Be aware of internet search options The veterinary technician plays a vital role in helping to educate clients regarding these parasites. It is important to pay close attention to the life cycles of these parasites because they contain important bits of information that are crucial to explaining the risks, methods of prevention, and reasons why the specific treatment intervals are important.

Trematodes Digenetic flukes (flatworms) Digenetic: definitive host plus two intermediate hosts Paragonimus kellicotti (lung fluke in cats and dogs) Schistosomes (blood fluke in wild birds; shown here) Trematodes are flatworms that parasitize a wide variety of domesticated and wild animals. These parasites are often associated with diseases of the intestinal tract; however, some digenetic flukes parasitize the respiratory passages.

Flukes Paragonimus kellicotti (lung fluke in cats and dogs) Eggs will float to top of most fecal flotation solutions Shown here: Operculated eggs of Paragonimus kellicotti. This is an unusual digenetic fluke that is found within the respiratory system; most digenetic flukes are associated with the gastrointestinal (GI) tract. Never allow dogs or cats to roam freely around lakes, streams, and ponds. Never feed raw crayfish to dogs or cats.

Cestodes and Metacestodes Cestodes: Adult tapeworms Intestinal tract of definitive host Metacestodes: Larval tapeworms Extraintestinal sites Types of cestodes Dipylidium caninum (shown) Echinococcus granulosus/Echinococcus multilocularis Spirometra mansonoides   Shown here: Dipylidium caninum, the cucumber seed tapeworm.

Cestodes (Tapeworms) The most common sign is the presence of gravid tapeworm proglottids (tapeworm segments) in the host’s feces or around the anus Dried-out tapeworm segments resembling dry uncooked white rice may be found in bedding   Shown here: Segments of Dipylidium caninum on fresh dog feces.

Dipylidium caninum Dipylidium caninum, the double-pored tapeworm, possesses two sets of both male and female reproductive organs, located laterally, next to the two lateral genital pores.

Dipylidium caninum Among tapeworm proglottids, both cross-fertilization and self-fertilization can occur. A mature proglottid has functioning male and female reproductive organs. Figure 14-9: Older, gravid proglottids contain a uterus filled to capacity with thousands of egg packets. Figure 14-10: Each packet containing from 20 to 30 individual hexacanth (six-toothed) embryos.

Dipylidium caninum Figure 14-11: The hexacanth embryo is eaten by a larval cat flea), the intermediate host for this tapeworm. Figure 14-12: Within the larval cat flea, each ingested hexacanth embryo develops into a cysticercoid, the infective stage of the tapeworm. For each cysticercoid that is ingested by a dog, cat, or child, one adult tapeworm will form.

Echinococccus granulosus The definitive hosts, primarily canids, harbor the adult stages of the tapeworm in the small intestine The intermediate hosts, sheep and cattle, harbor the larval stage of the tapeworm in a variety of visceral organs (the liver, the lung, and the brain) Humans are capable of serving as intermediate hosts for this parasite. Do not produce clinical signs in the canine or feline definitive host.

Echinococcus multilocularis The definitive hosts, primarily cats and foxes, harbor the adult stages of the tapeworm The intermediate hosts, microtine rodents (mice, voles, and rats), harbor the larval stage of the tapeworm, in the liver and lung Humans are also capable of serving as intermediate hosts for this parasite. Do not produce clinical signs in the canine or feline definitive host. Echinococcus species should be reported to state and federal authorities if an outbreak is suspected.

GI Nematodes (Roundworms) Round on cross section Parasitize widest assortment of wild and domestic animals; many organs/systems Types Toxocara canis/Toxocara cati /Toxascaris leonina (cats and dogs) Paratenic (transport) host Baylisascaris procyonis (raccoons) Ancylostoma aninum/Ancylostoma braziliense/Ancylostoma tubaeforme (dogs and cats) Many types of roundworms are associated with both dogs and cats. Of all the parasites covered in this chapter, these nematodes (roundworms) parasitize the widest assortment of wild and domestic animals.

Toxocara canis (Canine Roundworm) Dog must ingest this egg for the life cycle to continue Infective stage of Toxocara canis—an egg containing a second-stage larva. This stage is infective for the canine host. Usually diagnosed using fecal centrifugation/flotation techniques and proper identification of unique egg types.

Barylisascaris procyonis Mainly found in the small intestine of the raccoon definitive host, but can be found in dogs Similar to ascardis of dogs and cats Diagnosed using routine fecal flotation Keeping raccoons aspets should be strongly discouraged.

Ancylostoma (Hookworm) Found in small intestine of dogs and cats Voracious blood feeders Diagnosis: Fecal centrifugation/flotation of fresh feces and egg identification Anterior end of adult Ancylostoma caninum. Note three pairs of ventral teeth and the large buccal cavity.

Trichuris vulpis (Whipworm) Fresh fecal sample is best for diagnosis Identify unique whip-like shape (fat posterior handle with long, filamentous anterior end) Unique trichinelloid egg type. Figure 14-24: Whip-shaped adult of Trichuris vulpis with its thin anterior end and its fat posterior end. Figure 14-25: Bioperculate, symmetric, yellow, football-shaped egg of Trichuris vulpis. Extremely rare in United States but occasionally seen in felines.

Strongyloides (Intestinal Threadworm) Strongyloides larvae (L1 stage) Fresh fecal sample, Baermann technique Mucosal scrapings may reveal adult female parasites, eggs, and first-stage larvae   Small intestinal mucosal scraping, revealing adult females, eggs, and first-stage larvae of Strongyloides stercoralis. There are no parasitic male Strongyloides stercoralis.

Enterobius vermicularis Human pinworm; pseudoparasite of cats and dogs NIH Scotch tape test Characteristic asymmetric ovum Characteristic asymmetric ovum of Enterobius vermicularis.

Protozoans Unicellular Giardia Toxoplasma gondii Humans, pets, contaminated water Toxoplasma gondii Only cats harbor sexual stages; other mammals intermediate hosts Cryptosporidium parvum Intestinal No reliable treatment Infected dog must be isolated from other pets, children, and individuals with compromised immune systems Some protozoans are parasitic in human beings and in wild and domestic animals. Based on the means of movement, protozoans can be broken down into several types: Ciliates (moving by means of tiny beating “hairs”) Flagellates (having one or more whip-like flagella) Amoebae (moving by means of pseudopodia) Apicomplexans (moving by gliding)

Giardia Humans, pets, contaminated water Cysts and trophozoites on direct fecal smear Zinc sulfate flotation medium with centrifugation Figure 14-34: Cyst of Giardia species. Figure 14-35: Trophozoite of Giardia species.

Cryptosporidium parvum Smallest protozoan parasite in GI tract All domestic animals Tips of villi in small intestine Diagnosed by fecal flotation No reliable treatment Oocysts of Cryptosporidium parvum, fecal flotation.

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