INFECTIOUS DISEASE RISKS TO PARROT …...INFECTIOUS DISEASE RISKS TO PARROT AVICULTURE AND...

INFECTIOUSDISEASE RISKS TO PARROTAVICULTURE AND REINTRODUCTIONAG.GreenwoodMA,VetMB,MlBiol,MRCVSInternationalZooVeterinaryGroupKeighley,WestYorkshire.

IntroductionParrots, asa family among birds,seemto be susceptible to a largenumber of highly contagious mainlyviral diseaseswhich may havesevereeffectson captive popula-tions, particularly those maintainedunder intensive conditions. Most ofthesediseasesare potentially fatal,someuniformly so,whilst othersmay decreaseproduction or theviability of offspring. Somehavelong incubation periods of up toseveralyears which, coupled with alack of tests for the carrier state,enablethem to infect whole groupsof parrots undetected. Vaccinesaregenerally unavailable or marginallyeffective.An understanding of thesediseaserisks is very important forthe maintenanceof parrots incollections and, particularly, fortheir safetransfer betweencollections and eventualreintroduction into the wild.

Diseaseswhich will beconsidered in this paper are:

Herpesvirus (pacheco's disease)

Polyomavirus (avian papovavirus)Psittacine beakand feather disease

Proventricular dilatation disease(Macawwasting disease)

Internal papillomatous disease

Chlamydiosis (psittacosis)There areother virus and

infectious diseasesof parrots, butthey are of lesser importance in thisgeneralcontext.

1.Psittacine herpesvirus infectionThis virus, oneof a group of avianherpesviruseswhich includes falconherpesvirus,pigeon herpesvirus,Marek'sdiseaseand others, is verycommon in shipments of New Worldparrots, particularly Amazons.Mostinfected birds die during quarantinewith acutesevereliver disease,butothers p1aybe unrecognisedcarriers. Caseshaveoccurred in UKcollections after several yearswithout the introduction of newbirds. Herpesviruscarriers typicallybeginshedding virus, or become ill,becauseof some intercurrent stresssuch as breeding,dietary change ortransport. Avaccine is available inthe USand hasbeen used in SouthAmerica before shipment but withvery poor results, possibly becauseof strain variation within the virus.The humanantiviral drug acyclovir

(Zovirax) is effective at stoppingoutbreaks, but there is usually toolittle warning to savethe individualbird. It is not known, however,whether the recovered birds mayremain carriers.

Serological and virus isolation(from faeces) tests are available, butthe former cannot distinguishcarriers from non-carrier contactsand the latter depends on the birdshedding virus.

Appropriate precautions arequarantine and testing of incomingbirds. Probably faecal culture isworth doing as a newly arrived birdmay shed virus under stress.Treatment of detected carrierswould be controversial. The virusoccurs naturally probably only inNew World parrots and there iscircumstantial evidence that someconures may be regularsymptomless carriers. It is thereforewise to keep Old World and NewWorld species separate and avoidmixing conures with Amazons andmacaws.

2.PolyomavirusThis highly contagious virus is theonly member of its family whichcausessystemic diseasein anyspecies. The rest cause typicalinfectious papillomas or warts. Inparrots, only chicks are clinicallyaffected (with a few recordedexceptions) but the disease iswidespread in captive populationswhere the adults are carriers. Some50%of Germanand USaviariestested positive in serologicalsurveys. The prevalence in Britain isunknown. The virus is spreadhorizontally between chicks innurseries, and probably betweensymptomless adults. It is almostcertainly vertically transmittedthrough the egg.Most species oflarger parrot are susceptible andchicks die at 3 to 16weeks,or maysimply be very difficult to rear withrepeated bacterial infections andpoor growth rate. Diagnosis innurseries may sometimes bepresumptive, based on constantrearing problems correlated withserologically positive adults. Testingis difficult to interpret as sero-negative adults can be shown toshed the virus. The development ofhighly sensitive tests for viral DNAin droppings and tissues is likely toimprove the situation in the nearfuture. The host-virus relationship ishighly complex and makespre-diction of carrier or immune statusvery difficult.

Appropriate precautions are

difficult to take. At present we cantest adults in quarantine by serology(in Germany),with the caveatsoutlined above.There are noeffective treatments or vaccines.Prevention of spread betweenchicks is crucial, always remem-bering that the symptomless chickmay be the culprit and that the virusis easily transmitted and veryresistant to disinfectants. Hypo-chlorite should be effective.

3. Psittacine beak and featherdiseaseThis disease is now known to becaused by a circovirus and causesfailure of feather and beak growth inall species of parrots, but is chieflyseen in cockatoos, African greys andlovebirds. Infection seemsonly tooccur in young birds, which may dieof acute liver disease,becomesymptomless carriers or demon-strate the classic signs at subse-quent moults one or more years inthe future. The virus affects therapidly multiplying epithelium of thefeather and beak causing new pinfeathers to become pinched off ortwisted and the beak to become firstshiny and then to crumble away.There is no effective treatment forcarriers or clinical cases.Genera-lised immunosuppression iscommon and the bird may die ofsome other unrelated infection.Extensive studies have taken placein the USAto produce a test forcarriers and a vaccine but neither iscurrently available in the UK.Affected birds can be tested by thehistological examination of adamagedfeather and its follicle, andspecific inclusions can be identified.The disease has occurred asdevastating outbreaks in parrotnurseries and frequently leads tothe euthanasia of affected adultbirds. Somecarriers can probablyremain normal for life. It is nowknown that the virus can be egg-transmitted.

Precautions include quaran-tining any incoming birds, especiallycockatoos, for long periods,elimination of breeding birdsdemonstrated to be infected by thepresence of disease in their chicks,and introducing chicks intonurseries only if they have beenincubator hatched. The disease isspread by parents to chicks in thenest by feeding, and between chicksby feather dust and dried faeces. Itis even possible for the disease tobe introduced by feather dust onkeepers' clothes!

4. Proventricular dilatation disease

(Macaw wasting disease)This disease affects many species ofparrots, particularly macaws,African greys and cockatoos. Adultbirds waste and die after periods ofregurgitating seed and passingundigested food in the faeces,whilststill eating well. There may benervous signs, although these aremuch more common in chicks,which may show changes in voice,unusual begging behaviour andparalysis as well as regurgitation.Outbreaks occur in intensive parrotunits but more often casesaresporadic. The diseaseis clearlytransmissible but no virus hasyetbeen definitively associated with it.The clinical and pathological pictureare classical, but there are otherdifferential diagnoses,such ascandidiasis or gastric foreignbodies. No bird should be labelledashavingMWD unlessadefinitivediagnosis has been made in anexperienced laboratory, becauseofthe potential implications for thecollection.

There is a very long latentperiod and the diseaseseemsto bespread by carrier birds which donot necessarily succumb to stress,but infect other birds when movedinto a collection. Other birds maythen die up to a year later.Consequently it may never bepossible to decide which bird wasresponsible for introducing thedisease.Once in a collection itcannot be eliminated by removal ofcarrier birds, although parents ofaffected chicks must be suspect,provided there has been no spreadwithin the nursery. Infection isprobably also spread indirectly bykeepers as casesseemto crop uphaphazard in a house rather thanpassing from one cageto the next.As no virus hasyet been isolatedthere are no tests for carriers andno real treatment is possible.

Precautions against intro-duction of the diseaseinclude longquarantine periods, thoroughknowledge of the origin of birds,X-ray examination of birds whichbecome or remain thin during thequarantine period, and hygienicprecautions to prevent spreadbetween aviaries.

5. Internal papillomatous diseaseCloacal papillomas occur frequentlyin New Worldparrots, includingAmazons, Greenwinged macaws andHawkheads, and are usuallyrecognised by the presence of freshblood in the faeces or frank cloacal

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prolapse. It is less commonlyrecognised that similar polyp-likelesions occur on the palate andglottis and even in the upperoesophagous. The disease appearsto be transmissible, although nocause has been isolated, and is oftenspontaneously self-curing.Treatment by surgical removal ofthe papillomas can be difficult anddamaging although the use of laserslooks promising. About 10 percentof affected birds have an associatedpancreatic atrophy and bile-ducttumour, which is usually fatal. It isnot clear how many affected birdsmay develop this sequel later in life,but the disease should obviouslynot be considered to be merelybenign. Some liver function testsshow promise in identifying suchbirds at an early stage.Transmission is believed to be byoral or venereal contact betweenbirds and there is concern that

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breeding may be affected.Incoming birds of susceptible

species should undergo a thoroughcloacal and oral examination as partof their general clinical check beforeentering the collection.

6. Chlamydiosis (psittacosis)This disease of all birds is well-

known in parrots, but muchmisunderstood. Emphasis tends todwell on the potential infectivity forhumans and frequently leads tooverreaction in this regard, whenthe main threat is to the birds. The

infectious agent is a primitivebacterium but, being cell-associated, has many similarfeatures to viruses, including beingvery indestructible in its restingstage. It is susceptible to antibiotics,including tetracyclines anderythromycin, when activelymultiplying, and there are tests forcarriers, so the outlook is more

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YoungLesserSulphur-crestedCockatoosufferingfrom a feathercondition

promising than for most viruses,However. a life-time carrier stateappears to exist. so this has to beincluded in the group of 'time-bomb'diseases. Infection is most oftenseen in newly imported New Worldparrots and losses can be massivein heavily stressed birds. Thewidespread illegal use oftetracycline antibiotics inquarantine frequently leads tosuppression of the disease, so thatthe parrot falls ill on the next owner,when antibiotics are withdrawn andthe stress of movement is added.

Chlamydiosis is typically manifest attimes of stress such as change ofownership, breeding, bad weatheretc. The clinical syndrome varieswith species - some, such ascockatoos, seem to be resistant,others like cockatiels and

budgerigars may have persistentsubclinical infection, whereasAmazons may develop severehepatitis and die quickly. Australianparakeets tend to get mild eyedisease and coryza. Some flocksmay only suffer poor egg productionand lowered hatchability.

Diagnosis is possible fromclinical signs, but there are nowvery sensitive faecal tests forchlamydial DNA(Central Vet Lab,Weybridge) which can detect manycarriers as well as clinical cases.Frequently the presence of thedisease is only suspected when ahuman case occurs. Chlamydiosis isnot notifiable (except inCambridgeshire) and officials haveno rights to dictate the managementof infected birds, although there areHealth and Safety implications inzoos. In any case, the response ofofficials is usually wrong. Positivecases should be isolated and

correctly treated, tested aftertreatment is complete and thenreturned to the collection, orallowed to enter it, while carrying a"flag" against their name as apossible carrier (with Iowprobability).

Incoming birds can be tested inquarantine, preferably twice, with agood likelihood of success as thestress should cause them to become

shedders. There is no justificationfor random treatment or treatment

of quarantine birds. Spread betweencages seems to be low, but is highwithin cages. Frequently the onlysign that a bird is a carrier is whenthe new mate to which it is

introduced goes down with thedisease. Because of widespreadcarrier states in parakeets,cockatiels, budgerigars and finches,large parrots should be kept wellaway from these species.

ConclusionThe foregoing should make clearthat the maintenance of closed

aviaries of parrots is the ideal. Ofcourse, this philosophy isincompatible with jointmanagement of species and thepairing of unrelated birds.

Nevertheless, it appears thatdiseases like MWDare increasingexponentially in captive parrotpopulations and any establishedbreeding collection would do wellnot to add to its numbers from

unknown sources unless absolutelynecessary and, in these cases, toquarantine and test incoming birdsexhaustively. The expense of suchprocedures should be well repaid intime.

One alternative would be to setup a system of certifying collectionsas free of certain diseases. In theabsence of definitive tests this canbe difficult, but it should bepossible to a limited degree ifcertain criteria are met:-

a. All parrots, chicks and eggs dyingin the collection should be

examined post mortem, by acompetent laboratory with aknowledge of parrot diseases.b. All sick birds and chicks shouldbe examined clinically and anaccurate diagnosis made (as far aspossible).c. All birds should be testedregularly for those diseases forwhich tests are available, andclinically examined for signs ofothers (e.g. beak and featherdisease, papillomas) on an annualbasis.

d. Records should be kept ofoffspring from the collection, theirdestination and eventual causes ofdeath.e. There should have been no

incoming birds during the periodcovered by the ,certification.

It should then be possible tomake up further breeding groupsusing offspring from certifiedcollections which should, bydefinition, be free of the majorinfectious diseases. Such offspringwould be prime candidates forreintroduction projects as, with theexception of beak and featherdisease, we have no knowledge ofthese conditions among wildpopulations and cannot know thepossible consequences ofintroducing them either to naivepopulations or virgin habitat. Theability of other carriers than thebirds themselves, particularlyvisiting aviculturists and evenveterinarians, to introduce diseaseaccidentally should not beoverlooked.

Infectious disease represents amajor threat to the viability ofcaptive parrot populations in a waythat is probably unique in the zooworld. Tremendous efforts are beingmade to come to grips with theseproblems prompted, it has to besaid, by the economic pressures ofAmerican aviculture rather than bythe efforts of zoos. Nevertheless,complete success and security areclearly some way in the future anaitis vigilance now which will ensurethat we have breeding birds andoffspring for reintroduction in thefuture.

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