Management of Atoxoplasmosis in a Mixed-Species Aviary
American Association of Zoo Veterinarians Conference 2008

Steve Unwin1, BSc, BVSc, MRCVS; James Chatterton1, BVM&S, MRCVS; Julian Chantrey2, BSc, BVM&S, PhD, DRCPath, MRCVS; Stephanie Sanderson1, MA, VetMB, MSc (WAH), MRCVS

1Conservation Medicine Division, Chester Zoo, Chester, UK; 2Department of Veterinary Pathology, University of Liverpool, Leahurst Campus, Neston, UK


Atoxoplasma spp. are protozoa of the Eimeriidae with a direct life cycle,2,6 affecting a number of passerine species.1,3 They appear to be host specific.6 Atoxoplasma constitutes an extremely difficult and controversial parasitic pathogen to manage in captive passerine birds.3 Unlike other Eimeriidae species, the asexual life cycle of Atoxoplasma takes place in internal organs (often the liver) and not in the intestinal mucosa,6 making antemortem diagnosis challenging. Polymerase chain reaction (PCR) studies have shown Atoxoplasma to be common subclinically.1 This disease is known to be circulating in UK passerines but is not thought to be associated with clinical disease.4 A PCR test for Atoxoplasma developed in the USA3 is unavailable in the UK, but we are investigating the possibility of developing one in the UK.

This case is the first recorded and confirmed report of Atoxoplasma in the pied starling (Spreo bicolor).

Archived pathology records at Chester Zoo (1999 to 2007) were reviewed. Atoxoplasmosis was first confirmed in a Bali mynah (Leucopsar rothschildi) in quarantine in 2000. Atoxoplasmosis was not positively identified within the collection until 2006 in juvenile pied starlings in a naturalistic outdoor aviary (Arcade), and in 2007 in a recently fledged emerald starling (Lamprotornis iris) in an indoor tropical free flight aviary (Table 1). Hepatomegaly was the most consistent feature on gross postmortem evaluation. Histopathology revealed most sinusoids were expanded diffusely by moderate numbers of mixed leucocytes, with many hepatocytes and macrophages containing abundant hemosiderin. Merozoite-like protozoans were found within macrophage cytoplasm and less overtly free in the liver, spleen, and small intestinal mucosa.

Table 1. Atoxoplasmosis findings (confirmed and suspected) at Chester Zoo 1999-2007


Suspected vs. confirmed


Aviary location


Time of year

Pied starling

Suspect (undetermined)



8 Day, 2 month 12 days (juveniles)

June to August 1999–2001

Pied starling

Suspect (coccidiosis)



1 Month 10 days, 1 month 18 days (recently fledged)

Mid-June to mid-July 2001–2003

Bali mynah




9 Months 17 days (young adult)

End August 2000

Pied starling




1 Month 20 days (recently fledged)

Mid-July 2006

Pied starling




16 Days (nest bound)

End July

Emerald starling



Tropics free-flight

28 Days (fledgling)

June 2007


All these animals were parent-raised in the respective aviaries. There was no movement of birds between these aviaries during this time, as part of our management plan. On review, there had been 13 pied starling deaths possibly associated with atoxoplasmosis (Table 1). There have been no ‘sick birds’ in the collection with atoxoplasmosis or coccidiosis in general, making confirmed antemortem diagnosis challenging.

Fecal examinations for parasites in the tropical free-flight aviary have been negative for coccidian oocysts from 2001 until November 2007 when oocysts were found on a general sample. This remains the only positive sample from this aviary despite repeated sampling from June 2007 to March 2008, as we enter a new breeding season. There have been no further confirmed deaths due to atoxoplasmosis in any species since mid-2007. However, if there is a low-circulating infection in the tropical free-flight aviary, there is evidence that exposure to low levels of infection during chick development may help immune systems cope when challenged with a higher burden.3



Hand-rearing chicks to prevent exposure to Atoxoplasma. There is no evidence of vertical spread of atoxoplasmosis, but thorough cleaning of the egg, (done at Chester Zoo using F10 disinfectant [Health and Hygiene (Pty) Ltd, Sunninghill, South Africa] and UV sterilization) and removal of fecal material prior to incubation is essential. Note however, that birds not previously exposed to the organism may be more susceptible to high mortality when they are exposed.4

Targeted Therapy

Treatment to reduce the coccidial burden to increase the chance of juvenile birds surviving past fledging includes:

  • Monitoring feces for coccidial burdens monthly.
  • 1.25 mg Chlozuril (Appertex™ Janssen Pharmaceutica, Beerse, Belgium) per bird based on Samour 2000.5 The first year of using this treatment in pied starlings (2006) was the first in five years that several chicks fledged successfully and 2007 was the first year all fledglings survived.


Newly acquired passerines are quarantined and screened with multiple fecal flotations (minimum of three every seven days) for coccidian oocysts. If any passerines show clinical signs in quarantine, or fecals show Isospora-like oocysts, blood collection and examination of buffy coat smears for Atoxoplasma will be undertaken. This test is specific but not very sensitive (unless the bird is showing clinical signs), thus the investigations to produce a PCR.

Overall Recommendation

Birds in large multi-species aviaries such as Chester’s tropical free flight are difficult to treat effectively. Thus, this aviary should be primarily for display purposes and not house Atoxoplasma-susceptible species or individuals that are critical to breeding programs.

Literature Cited

1.  Adkesson MJ, Zdziarski JM, Little SE. Atoxoplasmosis in tanager. J Zoo Wildl Med. 2005;36(2):265–272.

2.  Ball SJ, Brown MA, Daszak P, Pittilo RM. Atoxoplasma (Apicomplexa: Eimeriorina: Atoxoplasmatidae) in the greenfinch (Carduelis chloris). J Parasitol. 1998;84(4):813–817.

3.   Norton TM, Neiffer DL, Seibels B, Benson K, McAloose D, Travis D, et al. Atoxoplasma Medical protocols. The AZA Passerine Atoxoplasma Working group. Accessed 2003. (VIN editor: link was not accessible as of 1/18/2021.)

4.  Pennycott TW, Ross HM, McLaren IM, Park A, Hopkins GF, Foster G. Causes of death of wild birds of the family Fringillidae in Britain. Vet Rec. 1998;143(6):155–158.

5.  Samour J. Avian Medicine. London, UK: Harcourt Publishers Ltd; 2000.

6.  Sandmeier P, Coutteel P. Management of canaries, finches, and mynahs. In: Harrison R, Lightfoot T, eds. Clinical Avian Medicine. Palm Beach, FL: Spix Publishing; 2006:901–902.


Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

James Chatterton, BVM&S, MRCVS
Conservation Medicine Division
Chester Zoo
Upton, Chester, UK

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