pemesxTKs&F AYYLE

Skin / Subcutaneous tissueTicks - /xoddes rcr?rs

, Mites - Chor,aples bovis+ Demadex bovts

q.r^^,o< c.rhat

Pso0pies o visLice - Damalinia bovisFl es - Hypaderma bovis

LiverCysticerc us te nuicollis

Fasciola hepattcaHydahd cysis

Oesopha gusHypoderma lineatum

AbomasumOsteftagia oste,tagt

Heart and MusclesCysticercus bovisSarcocysts bovls

LUngsDiclyacaulus vtvparus

Hydalrd cysts

BloodBabesia divergensBabesia bovis

Parasites of cattle

P{RASITISM

:.:rasites can be defined as plants or animals that live on or within another, rng organism at whose expense i t gains some advantage whi lst giv ingthing in return. The host/parasite association can be complicated. The typeparasite encountered ranges fiom viruses (intracellular parasites) that canlr reproduce in a l iv ing cel l , to protozoa (single cel led organisms) to

' :JStinal worms and insects. Although they are palasitic, viruses are generally3rted as a separate

-sroup, and we will only be considering parasites that

-::' internal (endoparasites) and external (ectoparasites) that affbct cattle.Parasites may have a direct or indirect lifecycle. A direct lif 'ecycle means

-r.rt the parasite can only complete it 's lifecycle by parasitizing the host.

E\DOPARASITES

.OST / PARASITE RELATIONSHIP

.5e l i fecycles of parasi tes vary, but endoparasi tes undergo a three-step,..ociation with the host animal. Firstly, the parasite must infect the host via:.: intestines, respiratory system or the skin. Secondly the individual parasite

t",np;tSection 3must be maintained within the host, this includes feeding, growth andmigration within the host. Thirdly the species must be maintained, whichmeans reproduction and the dispersal of the infective agents.

Each of these stages of association present different hurdles for

INFECTION

the parasite.

Obviously the initial stage of parasitic development is gaining entry to thehost animal. The parasite has to survive in some form in the atmosphere.whi lst remaining avai lable to enter the host. The l i fecycle of mostendoparasites includes a hibernation stage, for example as a cyst or egg (theinfective agent) where the immature parasite lies dormant until suitableconditions trigger the release of the agent. The availability of the infectiveagent to host entry is achieved in various ways; some stages of a lifecyclemay include the infective agent existing in a secondary or*intermediate hostsuch as worms, beetles or ants that are ingested by the primary host. Thesingle oveniding factor in the availability of the infective agent to host entryis mathematical. Infection of the host is a matter of chance; the vast numbersof infective agents produced by the adult parasite increases the odds.

Cattle are important in the respect that they not only act as the final host toparasites; they also act as intermediate host in the lifecycle of a humantapeworm, human infection occurring when a viable cyst is ingested inundercooked beef.

INDIVIDUAL MAINTENANCE

Once the agent has entered the host's body, by whatever means, it has to beable to migrate to its preferred site of habitation (predilection site), where itcan mature. This can involve migration through body tissue or at the veryleast passage through the digestive system. Some parasites use the digestiveprocess to activate the infective agent, others produce secretions to neutralisethe effects of the gastric juices. The migration and settling of the immatureparasite will also prompt the host animal's immune response to a foreignagent, this is overcome by some parasites by protective secretions, and activelyencouraged by others as part of their lifecycle, using the immune response toisolate them and encase them in fibrous material where they form cysts.

PARASITE MAINTENANCE

On reaching the site where they mature, the parasite takes nutrients from thehost to mature. A successful parasite can be considered one that infects, lives.reproduces and infects other hosts without killing the primary host.

Parasites of catile(i, .rW,,' '

SPECIES MAINTENANCE

The role of any organism, from bacterium to human, is propagation of thespecies. E,ggs are passed by mature parasi tes in the faeces, and becomeinfective agents, and the cystic stages of other parasites gain entry into thehost through ingestion.

CYSTICERCAS BOVIS

Ct'sticercus bovis is the name given to the cysts formed by the embryos ofthe tapeworm of MAN, Taenia saginatcr, in the muscles of catt le, theintermediate host. The cysts are greyish-white, round and up to lcm inJiameter. The fact that this is a human tapeworm increases its significance innieat inspect ion, and most countr ies inspect ion procedures give specif ic:ctions to be taken on discovering the cysts in the carcase.

In humans the tapeworm inhabits the small intestine, the adult growing toretween 5 and 15 metres in length. The worm consists of a head with four.Lrckers, a neck and a chain of segments (proglottids) forming the stroblia.Elch proglottid is budded from the neck and becomes mature as it movesIrrrvn the chain. When mature the hermaphrodit ic proglott ids produce,pproximately 250,000 eggs (embryophores) which either pass out in the;eces through a genital pore in the proglottid, or are passed out in a shed

:roglottid which then disintegrates shedding the eggs. Each egg contains a.-ngle embryo (onchosphere.)

A C.bovis cyst in a heart. Note the way the cyst protrudes liom the cut surface.

i',: ibb ji'):-:1'aSection 3

Lifecycle of theTaeniu

human tapeworms{tginat$

NIan becomes infcted byingesting viable eysts inundercoohed beef.

- , l - : '

In nan

Adult womLength5-1-5 metres Lrves utsmall utestine Sogmelts(prtrglottrds) bud liom neckendmatwe os ihey mdve.1own tonn Each proglottidcontaxrs appllrxmatell25001t0 eggs (enbryophoresl

Eggs {rd met[c proglottidsare passed dailv in I'aeces

Proglottid r Embryophorc

r ltoglottids degenerate in

. atmosphere releasing eggs. \l1ien' mgested by the inLemednte host

I (cattle), th digostive lurces,' drssolve the embryophcrre md

i ectilBte the 1Na (onchosphere)

-' The onchosphere moves ikough

-: dle lining of the intestines an.l

7 enters the bloodstream and is

,,, cdried bc the preferrcd srtes lbr

..: enrystrg

A,W

Ctsticucus bais.@, ffi

In Cattle

The lifecycle of Taenia saginata involves cattle as the intermediate host.When cattle ingest the embryophores with grass the digestive juices dissolvethe embryophores and activate the onchosphere. The onchosphere travelsvia the bloodstream to its predilection sites (muscle with a good blood suppllsuch as the heart, masseter, tongue, diaphragm etc.) where it forms a fluidfilled cyst, a cysticercus. When viable, the cyst is transparent. The cyst canbecome enclosed (caseous) by the action of the bodies' immune system:after a period of time the cyst can become completely calcified at which

lflen the onchosphueanivos at the predilectionsltes lnuscles rvifi e goodblood supplr) it clerelopsint(, s e)it This bccomcsinlectile to mm efter ll1:l weeks andremainsinfectl'e (viablel lc.r up to2 tears

d"

Portt,sites of cotle l0t

:oint it is inert. Man ingesting the viable cyst in undercooked beef completes.he l i fecycle.

At the inspect ion point certain legislat ive procedures are fol lowed to.pecif ical ly examine for Cr ' .sr lcerctt .s hov, is, includin-u the incision of the:rasseter and ptery-eoid muscles of the head. palpat ion of the tongr"re and.kir t and visual examinat ion and incision of the heart . I f cysts are found.hroughout the carcase, both the carcase and offal are rejected as r-rnfit forrLlman consumption. If one viable or caseous cyst is for-rnd the aflected partr: rejected and the remainder of the carcase is refiigerated at either -7"C forl1 days or -10'C for 14 days before bein-e passed as f i t for human:onsumption.

FASCIOLIASIS

Fascioliasis is the terrn given to the chan-se of state in cattle due to the actionsol the liver fluke, a parasitic trematode called Fctst:iolu hepatictt.

Fasciolu hepoticcL has a complicated lif 'e cycle, (see diagram for summary.)involving the mud snail Lt'nutcre(t truncotltlo. CaItle pastured in damp fieldsbetween May to June and Au-eust to October are part icular ly suscept ible asthis is when the temperatLlre. condit ions. and snai l populat ion favour theparasi te.

Fasciol iasis may be acute. sub- acute or chronic. Catt le tend to rarelysuff-er fr-om acute fascioliasis as they do not eat grass down close to the

-eroundl 'n,ater level (unl ike sheep); they therefore tend not to rout inely ingest the

Adttlt Fa s c i o kt lt e patic ct

' \ lo2 . l ) Seuion 3I )-Dq"

infective metacercaria that encyst at the water level of the grass.Acute fascioliasis occurs 2-6 weeks after the beast ingests huge numbers

of metacercaria (2000+), and their subsequent migration through the livercauses massive haemorrhage and damage to the liver. Acute fascioliasis cancause sudden deaths in a herd during autumn and early winter.

Sub acute fascioliasis occurs, again, in autumn I early winter, whenmetacercaria are ingested over a longer period and the immature fluke are atvarying stages of development, some have reached the bile ducts and arecausing inflammation, others are still migrating through the liver substancecausins haemorrhages.

Distension of the bile ducts associated with chronic fascioliasis.

Chronic fascioliasis occurs normally in early spring; 4-5 months after 200-500 metacercaria are ingested. This form is the most common. The cattlesuffer loss of condition, emaciation due to lack of appetite and the effect ofthe fluke on the metabolism of food. Each fluke can cause the leakage of0.5m1 of blood into the bile ducts per day, as well as plasma proteins. Theliver is fibrous and the bile ducts inflamed (cholangitis.)

Submandibular oedema (bottle jaw) is a common clinical finding in chronicfluke infection.

Livers affected by adult fluke, or the migrations of immature fluke arerejected as unfit for human consumption.

Parasites of cqttle (l01ri!" "ffi-il'

Life cycle of the liver fluke Fasciola hepaticu

Mininmm 17-18 weeks ot optinruntenqrerolarcs.

Metacercaia.\!hm eato bv cattle. thecyst walls aro dig6ted,the young flukes whichemerge bore through the

walls ofthe gut and entathe body cavitv. AIle l-2

days thev bore throughthe liver surfae and fed

on livo cells, fmallyenteriug the bile ductsand grolv to rnatuiry

Cercaria'Whm

mature. theceraria pass out ofthe redia. lrErate tothe pulrnolarychambq ofthe snailand thn to theoutside. These fhenswim tluough rvaierfilrn to finn surfacessuch as grass mdencyst beconrmg aninfectivemetacorcaria.

M&tilre UvelJhr /.e live in the bile ducts ofthe liver, digeting secretions caued by theirpresmce. Eggs pass tluough the bile ducts to thentesllnes.

@Egg.

., Dgg passes in faeces.develops md hatch

ffi..R relcruing rn i rrcidia.

fffiR,'a]'es 9 daYS attemp

\|@ i:Yeen 22-26 des-ees

-\-z rErnrSr4us

Development on grass andin sheep. \

,,4t. Miracidium.ieg

iffi., lvlooue hfta wtucn must

.ffi^ iind a suitable snail'#ffi& within duehom as it

ffi ::::J:::,1."":#:,1,",.E[\ffi&lffi *+'""

Development in mud snailLvvnnuea truncalula

(Intermediate host)

":..- ,--z

SporocystApproximalely 30 minutsafter enta ing the snail theniraciditm dwelops into asporocyst in which thelan al redia are produced.

ffi1/K/'*

R\R.&\ffis'

,n,.,;""t ","r.,".*",#USsporocyst and slowlymigrates tkough the tissueofthe snail to reach thcdigestive gland. Here thecqqria are fomed rvithirthe redia.

The damage caused by the presence of fluke can also lead to conditions suchas Black disease, where spores of the bacterium Clostridium novyi gefininateand multiply in the fibrotic liver as the localised blood supply and thereforethe oxygen presence reduces, which could warrant the rejection of the entirecarcass as well as reducing the yield of that carcass

HYDATIDOSIS

Hydatidosis is the condition where fluid filled cysts of the intermediate stageof the tapeworm of the dog Echinococcus gronulosus are found in the internalorgans, normally the liver or lungs.

' ' ,{0t,,il Sec'rion 3*\ l r ,

Echinococcus granuloslzs is found in the canine intest ine and isapproximately 6mm in length. It consists of a head or scolex and three orfour segments. The eggs (embryophores) contain one embryo (onchosphere).which has six oral hooks, and are passed in the faeces at a rate of one perweek. The onchosphere can remain viable outside the host on the ground forup to two years.

When the intermediate host ingests the embryophore, the onchospherepenetrates the gut wall and travels in the blood to the liver, or in the lymphaticsystem to the lungs. Occasional ly onchospheres escape into the generalcirculation and cysts are formed elsewhere in the body.

A hydatid cyst in bovine lung tissue

Humans can also be intermediate hosts, when onchospheres are ingestedaccidentally from the coats of dogs or transferred by dogs when lickinghumans, or from eating vegetables or other foodstuffs contaminated by dogfaeces.

The cysts (hydatid) are slow growing, reaching maturity in 6-12 months.In the liver the cysts can reach a diameter of 20cm. Each cyst is fluid filledand contains a large number of scolices, which occasionally become detachedfrom the cyst wall and float freely in the fluid, giving rise to the term 'hydatidsand. '

The lifecycle is completed when a dog ingests the viable cysts.Offal containing hydatid cysts are rejected as unfit for human consumption.

Parasites of cattle fm\

LUNGWORM

The main lungworm of importance in cattle is Dictyocaulus viviparus, athread-like slender worm up to 8 cm in length that colonize the trachea andbronchi of the lungs.

DicQocaulus viviparus infection produces a condition known as husk orhoose. It causes chronic coughing and unthriftyness and severe cases canlead to lung oedema and emphysema. In the live animal the signs of lungworminfestation vary with the numbers of parasites involved. Mildly affectedanimals cough occasionally, especially during exercise. Those with a mediuminfestation cough at rest and have an increased breathing rate. Severelyaffected animals have a severely increased breathing rate and give theappearance of struggling for breath. Small calves are often most badly affectedand death rates amongst these can be high.

The adult worms live in the bronchi where they lay eggs. These hatch andthe larvae travel up the trachea to the pharynx, where they are swallowedand pass out with the faeces. They then move to grass where they are ingestedby other hosts. The larvae then penetrate the intestinal wall, pass to themesenteric lymph nodes where they moult. The larvae travel through thelymph ducts and blood capillaries to the lungs where they break into thealveoli (the blind ends of the bronchioles.) The final moult occurs in thebronchioles from where they move into the bronchi and mature. An incisioninto the lung tissue, cutting through the bronchi reveals thread like worms insevere infestation.

Lungs infected with Dictyocaulus viviparus are rejected as unfit forconsumption. Secondary infection by bacteria may warrant rejection of thecarcase if the infection becomes svstemic

SARCOCYSTS

Sarcocysts are a sub-group of s ingle cel led parasi t ic organisms cal ledprotozoa. They have a two-host lifecycle, the main species found in cattle,Sarcocystis fusiformis being transmitted in the faeces of dogs and foxes.Studies have shown that approximately 35Vo of sheepdogs and up to 75Vo ofhunting dogs are affected, possibly due to being fed undercooked beef.Another species Sarcocystis hominis is transmitted in human faeces.

Sarcocysts are the cystic stage of the lifecycle, which can be discernedwith the naked eye, and are found embedded in muscle. These cysts areknown as Meischer's tubes, roughly oval, up to 10 mm in length and are anoff white/green colour. The earlier stage, sporocysts, develop in and destroy