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24 Cards in this Set

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Describe the significance of nematodes
Nema = thread
-characteristic features of nematoda are:
1) unsegmented
2) acoelomate
-very few species are parasitic
-parasitic groups have evolved from free-living forms
Describe the morphology and features of nematodes
-nematodes are simple, tube-like animals with a mouth, intestine, and anus

Pseudocoelome - is the body cavity; the high hydrostatic pressure of the pseudocoelomic fluid provides rigidity to the nematode body

Cuticle - of nematodes is secreted by underlying hypodermis. Also lines orfices. Outer layer is a keratin-like protein; inner layer collagen. The cuticle is shed at each moult.

Musculature - longitudinal muscles only, in 4 groups. ACh involved in neuromuscular transmission. Blocking substances paralyse worms

Nervous system - nerve ring around esophagus with dorsal, ventral and 2 lateral nerves running posteriorly from it
-GABA in synapses
-some antihelmintics (Ivermectin) bind at post-synaptic GABA mediated ion channels point leading to paralysis

Digestive system - mouth enlarged to form buccal capsule with sclerotised walls
-important in identification, in determining the way nematodes feed and therefore the pathogenic effects they have on the host
-teeth may be present within buccal capsule
-cutting plates and teeth help in destroying host tissues during feeding
-nematodes may feed on gut content, blood or on the tissues of the host
-the esophagus acts as a simple pump to force food into the intestine. It frequently has valves
-intestine - a single ring of columnar cells, with micro-villi and brush border. Anus present in females; cloaca present in males

Excretory system - tubular. Opens to exterior at excretory pore on ventral surface, usually at level of esophagus. Paired glands open into pore. System is primarily osmoregulatory. Secretions of glands are highly immunogenic

Reproductive system
Male - testes are single & tubular. From testis a vas deferens leads posteriorly into a seminal vesicle and then via a muscular ejaculatory duct into the cloaca
Spicules - in male, usually elongate, pointed and contained within pouches in the side wall of the cloaca. Their function is to assist in copulation by dilating the vagina of the female and directing the flow of sperm
Female: one or two tubular ovaries containing germinal cells. A tubular oviduct lined with columnar epithelium leads from the ovary into a seminal receptacle which in turn opens into the tubular uterus
-female nematodes may be:
•Oviparous - eggs at the most segmented morula contained within when they are released from the female
•Ovoviviarous - eggs contain a fully developed first stage larva when released from the female worm
•Viviparous - eggs hatch inside the female and living larvae are released from the vulva
Describe the lifecycle of nematodes
-the original nematodes were free living, soil inhabiting, bacterial feeding organisms
-when other animals evolved they came into contact accidentally
-there are 2 ways into a particular host, through the mouth and through the skin

✰OXYURIDA
-evolved as parasites of insects
-could not penetrate the hard exoskeleton but were accidentally ingested
-eggs were passed out into the faeces and were re-ingested by the insect
-when vertebrates appeared, this very simple life cycle was adapted to vertebrates including man

✰STRONGLYLIDA
-carnivores have soft skin → can stay at site of penetration or can get into veins or lymphatics → carried passively to lungs → burrows and breaks out into alveoli → follows path of least resistance to bronchi → swallowed and go into gut to lay eggs
-L1-3 are free living and L3 is ingested
-modifications:
→Metastrongyloidea or lungworms had life in the lungs

✰ASCARIDIDA
-parasites of the small intestine
-L1-L3 occurs in egg
-a small mammal (e.g. mouse) ingests the egg, L3 migrates to liver then to lung
-instead of breaking out into alveoli, the larvae pass through the pulmonary capillaries and are dispersed to all organs of the body based on blood flow
-here they encyst
-they only develop further if mouse is eaten by python
-the L3 develops in the python & lays its eggs
-this life cycle also occurs in dogs and cats, except in addition the egg can infect the dog & cat, and when the larvae reach the lungs they can either undergo a migration to tissue where they encyst (a somatic migration) or can break out into the alveoli, undergo a tracheal migration and return to the gut
-ascarid life cycles invariably have either a somatic or tracheal migration
-the encysted larvae in the dog and cat can be mobilized during pregnancy and migrate to the mammary gland and be passed to the offspring in the milk (trans-mammary transmission) or to the fetus (pre-natal transmission)
-in herbivores (horse, pig) only tracheal migration occurs

✰SPIRURIDA
-most members of the group occur in the upper part of the gut - the esophagus and stomach
-always have an arthropod as intermediae host ie. egg ingested by insect, the L1 develops in the egg, develops to L3 and L3 is ingested by definitive host
-main phenomenone we see in the Spirurda is the shift away from the gut to just about any site in the body
What is the significance of the order Ascaridida?
SIGNIFICANCE:
-Mammals, birds & other
-Common; usually young hosts < 1 year (Usually only young animals b/c older animals develop a strong immunity)
-Old animals can represent “reservoirs”
-Usually host- and site- specific (adults; mostly SI); other sites (larvae*)
-Some are zoonotic; can use paratenic/transport hosts (e.g., earthworms)
-Production losses & clinical disease
What are the features of Ascaradida?
✰FEATURES
•Usually large adults (5-15 cm; F>m = 2 spicules)
•Creamy colour
•Three lips and no buccal capsule
•Some have alae (= ‘wings’) and/or bulbus
•Thick-shelled (sticky) eggs
•esophagus may have a ventriculus
•males with 2 spicules
•very common parasite worldwide
What are the life cycles of Ascaradida?
✰LIFECYCLE
-eggs are usually thick-shelled & resistant
-larva develops to infective stage in egg and egg ingested
-larvae often migrate en route to final site
-may use transport hosts

✰LIFECYCLES
A. suum typical lifecycle:
-female lays large numbers of eggs (2 million/female/day) which passes out in faeces
-larva develops in egg to L3 infective stage. Takes 2-4 weeks with adequate temperatures, water, oxygen etc.
-eggs tend to be sticky with rough albuminous coat, and are very resistant and long-lived (disinfectant → little effect. Sunlight and drying → 1-2 weeks, good conditions → YEARS)
-pig ingests egg and it hatches in small intestine and the larva is activated. Earthworms can be transport hosts
-free larva penetrate mucosa of large intestine (SI), enter portal venules and travel to liver (4-5 days) and thence to the lung (12 days) hepatopulmonary migration
-in the lungs the larvae break out of the alveoli and enter bronchioles and then migrate up the bronchi to trachea, pharynx, and then swallowed and reach SI. This process is called tracheal migration or hepatopulmonary migration (HPM)
-L4 reach SI at about 2-3 weeks post infection
-sexually mature adults usually develop about 2 months after infection ie. PPP 2 months
What aspects of the life-cycle are important to control?
✰ASPECTS OF LIFECYCLE IMPORTANT TO CONTROL
1. Young animals clinically infected
-older animals reservoirs of infection
2. Eggs are very resistant - hard to decontaminate environment
3. Even in modern piggeries Ascaris still a problem. Use concrete farrowing pens, clean with boiling water and NaOH. Successful in controling Ascaris
What is the pathogenesis of infections?
1. MIGRATORY STAGES - liver and lungs can be affected due to larval migration, particularly with repeated infections and development of sensitisation in these organs
-residual "milk spot" lesions in pig liver causes condemnation of organs
-A. suum larvae in cattle lungs can cause anaphylaxis

2. Adults in/SI - less pathogenic - feed on gut content
-loss of growth in animals, poor condition
-worms may secrete anti-pepsin and anti-trypsin enzymes
-mechanical effects: due to large size and heavy burdens, can cause interference with gut function, obstruction of bile duct and pancreatic duct, perforation
What immunity results with A. suum?
-results from antigens released during larval migration in the host
-adults are ultimately eliminated, very few live beyond one year, and successive waves of larva have greater difficulty in completing their migration
-the larvae provoke a severe immune response, and this leads to most of the pathology in the liver and lungs - get massive cellular infiltration especially by eosinophils
-humoral antibodies can be demonstrated as well as cell mediated reactions
-reaginic antibodies are also produced and these may be responsible for the anaphylactic reactions provoked in some animals
What is larva migrans?
-the larval stages of ascarids are not very host specific, and eggs will hatch and the larvae undergo extensive migrations in a number of different hosts
-thus A. suum larvae may migrate in man, cattle, sheep etc. - leading to allergic manifestations
What is Ascaris lumbricoides?
-very similar morphologically similar to A. suum
-biologically distinct species
-found in humans
What ascarid occurs in the horse?
✰Parascaris equorum in horses, donkeys
-Pequorum was the first organism in which meiosis was described
-similar life cycle to A. suum
-eggs infective after 9 days at 35 oC
-common in foals, adult horses immune, expel burdens
-clinical signs similar to pigs → diarrhoea, colic, respiratory signs, liver damage. Peak egg counts in foals 15-18 weeks of age
Describe Toxascaris leonina
✰Toxascaris leonina
-cat, less frequent in dog
-eggs are smooth-shelled
-larvae hatch, penetrate mucosa of small intestine, return to lumen after 10 days, moult to L4 and adult
-prepatent period 74 days
-no tracheal migration
-rodents lizards, arthropds, earthworms may act as paratenic hosts - ingest eggs, larvae migrate into tissues and remain dormant until ingested by definitive host
Describe Toxocara canis, its appearance, lifecycle, effect on fogs, aspects of its lifecycle important for control, and human infection with this parasite
✰Toxocara canis
-common parasite of dogs
-of significance as zoonosis

✰IDENTIFICATION
-post-esophageal ventricularis and alae which taper posteriorly

✰LIFECYCLE
-egg thick-shelled, sticky, resistant to adverse environmental conditions
-first 2 moults occur within egg
-INFECTIVE STAGES in L3 egg
-if egg is ingested by a pup (to about 12 weeks of age), eggs hatch in small intestine, larvae migrate to liver, then lungs, moult in lungs and undertake tracheal migration; final moult occurs in small intestine; prepatent period 4-5 weeks
-if dog is adult, larvae pass through lung capillaries in migration and are distributed to various organs of body based on blood flow; larvae become encysted in various organs, principally skeletal muscle, and development is arrested
-in male animals, this pathway is a dead end
-in female animals, during last weeks of pregnancy, larvae become activated and migrate to uterus, cross placenta and are carried via umbilical vein to foetal liver, then lungs
-after the birth of the pup, the larvae undergo a tracheal migration and develop to adults in the small intestine
-pups may pass eggs at 3 weeks of age
-larvae also migrate into mammary gland and infect pups via the colostrum, then develop to adult in small intestine
-larvae may be passed in the faeces of young pups. The bitch ingests these faeces and can become infected by the larvae.
-paratenic hosts (mice, rats, lizards, birds, arthropods) are important. Larvae migrate to tissues where they remain arrested in development. If ingested by dog, larvae mature to adults without further migration

✰EFFECT ON DOGS
-young animals, particularly unweaned pups, are most severely affected
-clinical signs can develop in pups as young as 3 weeks of age; generally see failure to grow, pot-bellied appearance
-retinopathy detectable in 30% of adult dogs

✰ASPECTS OF LIFECYCLE WHICH ARE IMPORTANT FOR CONTROL
-mainly young animals that are affected clinically due to peri-natal infection
-must begin treatment at an early age
-eggs are very resistant - hard to decontaminate environment
-difficult to control paratenic hosts

✰HUMAN INFECTION
-an important cause of visceral larva migrans (VLM) or ocular larva migrans (OLM) in children who eated contaminated dirt or actual faeces
-larvae migrate to liver, lungs, then to systemic circulation
-larvae may lodge in retina causing impairment to vision
-other symptoms include liver enlargement due to larval damage, pulmonary symptoms, occasionally CNS symptoms
-Diagnosis by ELISA using antigens collected by incubating L3 in virto antigens; antigens highly specific for T. canis
Describe Toxocara cati
-common parasite of cats
IDENTIFICATION - post-esophageal ventriculus and alae which terminate abruptly
LIFECYCLE:
-basic lifecycle similar to T. canis, with tracheal migration
-trans-colostral infection occurs
-no pre-natal infection
-paratenic hosts important
-not major zoonosis
What ascarids occur in ruminants?
✰Toxocara vitulorum
-not common parasite
-almost exclusively a parasite of calves
-trans-colostral infection main route of infection; tracheal migration does not occur
-limited to north-east coast of Australia
Describe the control of ascarids
Control (C) = Management (M) + Epidemiology (E) + Treatment (T)
What treatments/drugs can we use to treat ascarids?
✰PYRANTEL
-pyrantel pamoate
-oxantel pamoate

MODE OF ACTION:
→inhibit choline-esterases
→leads to blocking depolarization of muscle cells
-pamoate salts relatively unsoluble, most pass through gut unabsorbed

SPECTRUM:
→highly effective against most nematodes except lungworms
→pyrantel/oxantel mixture (Canex plus) highly effective against common nematodes

✰PIPERAZINE
ACTION:
→blocks acetyl-choline receptors, hyperpolarizing nerve membrane, causing reversible paralysis
→expulsion of worms dependent upon peristalsis
-soluble, pharmacodynamics not well known

ACTIVITY:
→nematodes

TOXICITY:
→extremely low; can be used in very young animals and pregnant females

USE:
→cheap & safe; highly effective against adult ascarids; available as syrup or tablet

MEBENDAZOLE:
→requires course of treatment since in monogastric animals there is no "depot" for the antihelmintic and it is rapidly excreted
→daily treatment over several weeks during pregnancy will reduce but not eliminate larvae encysted in tissue

*NO DRUGS will completely remove larvae in tissues
Describe the lifecycle, pathogenesis, and important points related to control for Asacaridia galli and Ascaridia platyceri
Ascaridia galli
♦HOST: chicken, turkey, goose
♦SITE: small intestine

Ascaridia platyceri
♦HOST: captive parrots, budgerigars
♦SITE: small intestine

✰LIFECYCLE of A. galli
-L3 develops in thick-shelled, resitant egg (2 weeks)
-fowl ingests egg, hatch in small intestine, moult twice, emerge and develop to adults in lumen of small intestine
-larvae tend to be arrested in mucosa of small intestine → not many develop into adults. This is especially so in subsequent infections → birds become immune quickly
-transport hosts, especially earthworms may be involved in life cycle especially under free range conditions
-prepatent period = 6 weeks

✰PATHOGENESIS
-young birds mainly affected
-larvae in mucosa do most damage
-important nematode parasite of chickens
-A. platyceri commonly associated with mortality in caged parrots, budgerigars

✰IMPORTANT POINTS IN RELATION TO CONTROL
-young birds mainly affected
-direct transmission by egg of worm → important under intensive rearing
-transport hosts in range birds
-eggs resistant but moisture favors survival
Describe the lifecycle, pathogenesis, and treatment of Heterakis
Heterakis gallinarum
♦HOST: chicken, turkey, goost
♦SITE: caecum

Heterakis isolonche
♦HOST: pheasants
♦SITE: caecum

Heterakis dissimile
♦HOST: turkey
♦SITE: caecum

✰LIFECYCLE
-L3 develops inside resistant egg in 2-4 weeks
-eggs hatch in intestine, larvae pass to caecum
-moult in glandular epithelium
-prepatent period 24-30 days (3 weeks)
-earthworms act as transport hosts

✰PATHOGENESIS
H. gallinarum
→direct affect of worms is little
→main importance is as carrier of Histomonas melagridis →flagellate causing blackhead or infectious enterohepatitis in turkey
→ organisms invade ovary of Heterakis and is incorporated into the egg

H. isolonche
→is highly pathogenic in pheasants, causing nodular lesions in caecm and death of host

✰TREATMENT
-all broad spectrum antihelmintics
Describe the Genus Anisakis
-marine mammals
-few life cycles known; may go through copepod first; fish(es) are principle intermediate hosts
-larvae found encapsulated in body cavity and muscles of many species of marine fishes. Serious economic loss in fishing industry
-in countries where raw fish is eaten (SUSHI, ie. Japan), processing may not kill larvae. Freezing at -20 oC for 48 hours will kill larvae
-if ingested by man, larvae can penetrate gastric mucosa causing granuloma formation, acute GI symptoms or even death
-Contracaecum osculatum, an anisakid nematode, causes ulceration and granulation in stomach of the fur seal and sea lion, both "normal" hosts
Describe the lifecycle, pathogenesis, important points in control and treatment of Oxyuris equi
✰LIFECYCLE
-female passes to rectum after mating
-eggs laid on perineum especially at night
-L3 in eggs infective → eggs thick shelled, resistant
-host ingests eggs → hatch in small intestine, larvae migrate to large intestine
-L4 histotrophic
-prepatent period = 5 months

✰PATHOGENESIS
-adults feed on intestinal contents, non-pathogenic
-substrate containing eggs irritates perineum and horses may damage themselves trying to relive the discomfort

✰IMPORTANT POINTS IN CONTROL
-not very common any more as very easily removed by treatment
-life-cycle direct: infection by ingestion
-eggs sticky and resistant
-animals infect themselves by licking perineum and ingesting eggs
-DIAGNOSIS: use sticky tape attached to perineum to recover eggs

✰TREATMENT
-all broad spectrum anthelmintics
Describe the different OXYURIDAE
What is the difference between ascarids and oxyurids?