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
Trichuris spp. ‐ Whipworms; Treatment – Swine
- Fenbendazole or dichlorvos
Trichuris spp. ‐ Whipworms; Treatment – Cattle/Sheep
- various endectocides
Eucoleus (Capillaria) spp.; General Features; host specificity, site of infection, general key morphological features
- highly specific with respect to host and location
- hosts can be infected by numerous species although
these usually infect different predilection sites - all have prominent stichocytes around the prominent esophagus
- some use intermediate hosts
Eucoleus (Capillaria) spp.; Morphology ‐ Adults
- slender, uniform worms (25 to 90 mm)
- fine, hair‐like in appearance
Eucoleus (Capillaria) spp.; Morphology ‐ Eggs
- oval shell with prominent plugs at each end – shell irregular/wavy
- single cell fills yellow‐brown egg shell
- shell less smooth than Trichuris spp.
- smaller, <60 um in ruminants; <70 um in dogs
Eucoleus (Capillaria) spp.; Life Cycle
- both direct and indirect life cycles
- many use earthworms as an IH
- eggs in feces or urine as defined by the location of adults
- C. hepatica lays eggs throughout liver and these are released after the host dies
- moderately lengthy PPP’s ‐ 4 to 8 weeks if known
Eucoleus (Capillaria) spp.; Pathogenesis/Lesions/Clinical Signs
- generally asymptomatic or mild
- respiratory forms may cause wheezing or coughs
- direct damage to epithelium in massive intestinal infections may give rise to edematous enteritis, diarrhea and emaciation ‐‐ rare
- diagnosis usually made on fecal examination
Eucoleus (Capillaria) spp.; Treatment – Dogs/Cats
- both fenbendazole and levamisole have been shown to be effective
- both are off‐label usage
Capillaria spp. in birds; what species, site of infection, adult and egg morphology
Capillaria contorta, C. caudinflata, C. obsignata
* infect many different birds species
* Capillaria contorta in crop and esophagus
* other species in the small intestine
Adults: slender 10 to 70 mm long
Eggs: typical bipolar appearance (55 by 26 μm)
Capillaria spp. in birds; Life Cycles
- C.contorta and C.obsignata have direct life cycles
- C.contorta can use an earthworm paratenic host as well
- C.caudinflata requires an earthworm intermediate host
- earthworms eat eggs, larvae penetrate tissues
- birds get infected by eating infected earthworms
PPP: 1 to 2 months for all species
Capillaria spp. in birds; Pathogenesis and Clinical Signs; Capillaria contorta
- wall of crop thickened with numerous worms
- clinical signs non‐specific, weakness, unthriftiness
Capillaria spp. in birds; Pathogenesis and Clinical Signs; Capillaria caudinflata and C. obsignata
- edematous intestinal wall with reddish fluid
- heavy infections ‐necrosis of mucosa
- clinically, reddish diarrhea and emaciation
- decreased production parameters in layers/breeders
Dioctophyme renale
Giant Kidney Worm
Dioctophyme renale; General Features; hosts, site of infection, geographical location locally
- normally a parasite of mink but will infect dogs
- uses an invertebrate IH and often fish as PH’s
- usually infects right kidney
- infrequently found as a “surprise” during surgery if the worm is free in the abdominal cavity
- found locally in Thames river valley
Dioctophyme renale; morphology
- females up to 100 cm long and 1 cm diameter
- smaller males have a bell‐shaped copulatory bursa
- bright red adults usually seen coiled in one kidney
- eggs have typical bipolar plugs with a pitted outer shell (about 70 μm long)
Dioctophyme renale; life cycle
- eggs passed in urine ingested by annelid
- larva develops to infective form
- may pass up food chain in piscine DH’s
- dogs or mink eat IH or PH, larvae leave intestinal tract and penetrate kidney where they mature
- PPP‐3to5months
Dioctophyme renale; Pathogenesis/Lesions/Clinical Signs
- only one kidney affected ‐‐ Why?
- affected kidney completely destroyed, often only the capsule remains
‐ reduces renal function - eggs passed in urine
Dioctophyme renale; Treatment
- surgical removal of the affected kidney
Trichinella spiralis; morphology
- females, 3 ‐ 4 mm long and slender, uterus contains developing larvae
- males, 1.5 mm long, tail has two small cloacal flaps (arrows)
- Larvae shed by female worm into intestine
Trichinella spiralis; life cycle
- each host is both definitive and intermediate host
- Larvae ingested in muscle start infection
- Larvae develop to adults – mate – females lay about 1500 larvae
- Larvae distribute around the body
Trichinella spiralis; Pathogenicity/Lesions/Clinical Signs
- Human‐ fatal dose of larvae
= approximately 5 larvae/gram host body weight - Remember → 2 larvae ingested give 1500+ larvae in the gut and muscle tissue
‐ gastroenteritis and diarrhea
‐ migrating larvae and early muscle stages
> muscle pains
> inflammation and eosinophilia
‐ muscle biopsy can identify heavy infections
Trichinella spiralis; Diagnosis/Treatment
- no viable treatment – preventation important
- diagnosis
– “trichinoscope”
– serology for domestic swine herd exposure - usually associated with backyard swine, wild boar or bear meats
Oxyurids
pinworms
Introduction to the Oxyurids; General Features of Pinworms; hosts specificity, site of infections, hosts, pathogenicity
- highly host specific
- parasite of the large intestinal tract
Oxyuris ‐ horses
Enterobius ‐ humans
Syphacia ‐ rodents - usually not overtly pathogenic ‐ but often irritating
General Morphology of Pinworms; adults and eggs
- most small (exception Oxyuris in horses)
- long tapering tail in one or both sexes (thus “pin”worms)
- eggs tend to be oval, some operculate
> most are asymmetrical (flattened on one side)
General Life Cycles of Pinworms
- direct, relatively simple, life cycle
- eggs in feces or, commonly, females deliver them to perianal region (causes irritation and consternation)
- egg mature to contain larvae
- fecal‐oral transmission route
– often via contaminated surfaces - eggs hatch in intestine and mature in large intestine
- variable PPP
