6.12 – Nematodes III – Rhabditids, Enoplids and Oxyurids Flashcards
Introduction to Rhabditids;
Threadworms and their relatives;
General Features;
general habitat, hosts, size
- generally free‐living parasites that infect vertebrates only during part of their life cycle or accidentally
- Strongyloides spp. more actively parasitic, but even this group of worms can have free‐living stages
- mainly very small (some microscopic) worms
Strongyloides spp. ‐ threadworms; General Features; site of infection, hosts
- infect small intestinal tract (deep between villi)
- various species in assorted hosts
S. stercoralis ‐ dogs, cats, people, primates
S. papillosus ‐ ruminants
S. westeri – equids*
S. ransomi – swine*
Strongyloides spp. ‐ threadworms; morphology, adults, eggs, larvae
- “thread‐like” adults, only 2 ‐ 9 mm
- thin‐shelled eggs are oval, ~50 μm long and contain a developing L1
- in S. stercoralis the L1’s hatch and can be found free in the feces (Baermann technique)
- larvae measure about 400 μm
Strongyloides spp. ‐ threadworms; life cycle, transmission
- complete free‐living life cycle occurs with adult males and females producing eggs
- parasitic infections are direct transmission (+/‐ a free‐living phase)
- ## no parasitic males ‐ females produce fertile eggs mitotically that mature to L1’s (free or in shell)
- transmission can occur by various routes
‐ ingestion of L3’s (mucosal migration)
‐ skin penetration by L3’s (tracheal or somatic)
‐ transmammary transfer of L3’s - autoinfection of S. stercoralis is known in humans (implications for immunocompromised?)
- short PPP (as little as 2 days in piglets)
- generally cleared from immunocompetent animals by 6 months of age
Strongyloides spp. ‐ threadworms; Pathogenesis/Diagnosis/Treatment – Small Animals
- generally not pathogenic in small animals
- may cause a non‐bloody enteritis
- larvae in feces so require Baermann for sensitivity
- in dogs ‐ off‐label use of ivermectin (200 μg/kg PO ‐‐ Note: idiosyncratic drug response in collies and collie‐ crosses)
Strongyloides westeri ‐ Horses; Pathogenesis/Diagnosis/Treatment – Horses
- large numbers in duodenum and jejunum can cause inflammation, edema, erosion – enteritis
- young animals only
- karvated egsg on standard fecal float
- foals – oxibendazole or ivermectin
- mares – ivermectin during week after foaling to reduce larvae in milk
Strongyloides ransomi ‐ Swine; Pathogenesis/Diagnosis/Treatment – Swine
- usually a neonatal problem
- malabsorption and leakage from enteritis
- diarrhea ‐ dehydration
- larvated egsg on standard fecal float that must be differentiated from Metastrongylus
- levamisole, ivermectin, doramectin
Introduction to Enoplids (=Trichurids); what type of worms are included, general morphology, general hosts
- includes the whipworms, capillarids as well as the giant kidney worm (Dioctophyme)
- all have an elongate esophagus surrounded by specialized cells called stichocytes
- many different hosts infected by these worms but each species is specific for a particular host
Introduction to Enoplids (=Trichurids); Hosts and Locations Infected
- highly host specific
- location(s) in host vary by genus
‐ Trichuris ‐ cecum, colon
‐ Capillaria ‐ epithelium of intestine, respiratory tract or urinary tract
‐ Trichinella ‐ intestine (larvae in muscle) - adults often buried deeply in epithelium
Introduction to Enoplids (=Trichurids); morphology, adults, eggs, larvae
- adults ‐ usually slender, white
- eggs ‐ oval with distinct bipolar plugs
- larvae ‐ (formed by Trichinella spp.) are usually found in the intestinal tract or muscle cells
Introduction to Enoplids (=Trichurids); Life Cycle
- both direct and indirect life cycles
- larvae mature in eggs and infect the next DH or IH
- Trichinella larvae are released into intestine, penetrate the tissues and become hypobiotic within muscle cells (transmission by predation/scavaging)
- oral transmission is the normal route
Trichuris spp. ‐ Whipworms; general features; site of infection, hosts, general morpholgy
- parasite of the cecum and colon of a wide variety of mammals, including humans
- each host has its own species of Trichuris that will not infect other hosts – host‐specific
- generally, morphology reflects the shape of the adult worm (although it is a misnomer)
Trichuris spp. ‐ Whipworms; Morphology ‐ Adults
- shaped like a whip (anterior 2/3 narrow and the remainder much broader)
- some species up to 8 cm but many smaller
Trichuris spp. ‐ Whipworms; Morphology ‐ Eggs
- smooth oval shell with prominent plugs at each end
- single cell fills yellow‐brown egg shell
- > 60 μm in ruminants; >70 μm in dogs
Trichuris spp. ‐ Whipworms; Life Cycle
- direct life cycle
- infective eggs mature with an infective larva
- eggs environmentally resistant and frost‐resistant
- transmission by oral ingestion
- simple mucosal migration in small intestine before forming adults in the large intestine
- long PPP’s ‐ 2 months or more where known
Adult worms lay eggs inlarge intestine
>eggs passed in feces
>eggs embryonate
>embryonated eggs in feces
>embryonated eggs ingested by dog
Trichuris spp. ‐ Whipworms; Pathogenesis/Lesions/Clinical Signs
- long thin anterior portion of worm is deeply embedded into colonic epithelium (may actually penetrate into the epithelial cells)
- may cause malabsorption and protein loss
- malabsorption may lead to diarrhea
- some worms may blood feed and therefore blood in feces (What colour would it be?)
- clinical signs may occur during prepatent period
Trichuris spp. ‐ Whipworms; Treatment – Dogs
- few registered products compared with the number available for roundworms or hookworms
- fenbendazole, milbemycin, moxidectin, Pyr‐a‐Pam plus, Drontal plus
