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Journal of Clinical Microbiology, February 2005, p. 1005-1006, Vol. 43, No. 2
0095-1137/05/$08.00+0 doi:10.1128/JCM.43.2.1005-1006.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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Pairs of specimens were taken from 45 wild pink pigeons in October and November 2003. This number represented all the individuals from the only site in Mauritius that had adequate facilities to conduct rapid microscopy. Each individual was swabbed twice in the mouth, esophagus, and crop to obtain a sample of saliva and mucosal cells. The first swab was examined immediately by wet-mount preparation, and the second swab was used to inoculate the InPouch TF culture pack. The latter specimens were incubated at 38°C for up to 96 h and examined every 24 h. Trichomonads were identified microscopically in both methods by their characteristic morphology and motility.
Of 45 birds screened, a total of 27 (60%) tested positive for T. gallinae by the InPouch TF culture packs. Of these 27 birds, 12 were positive by wet-mount microscopy (26.7% of all samples and 44.5% of samples positive by culture). No infections were detected by the wet-mount method alone. All 12 of the infections detected by the wet-mount method were positive within the first 24 h of culture in the InPouch TF pack. Of the 15 infections that were not detected by the wet-mount method, 8 were detected after 24 h of incubation, 4 were detected after 48 h, and 3 were detected after 72 h. No further infections were found after 96 h of incubation.
Although wet-mount microscopy has been the standard diagnostic technique for determining T. gallinae infections in birds, the InPouch TF method detected more than twice as many positive infections as wet-mount microscopy (P = 0.001, two-sided Fisher's exact test). Previous investigations of T. gallinae in pigeons using wet-mount preparations may have underestimated the number of birds infected. For example, a previous study detected a prevalence of T. gallinae in pink pigeons of 18% using the wet-mount method (11). Our results suggest that the true prevalence of infection may have been closer to 40%. Wet-mount preparations have also been used to detect T. gallinae in other rare species of Columbidae, e.g., the Galapagos dove Zenaida galapagoensis (5). Results using this method will inevitably depend on the exact technique and equipment used, the screener's ability to detect the parasites in the preparation, and the intensity of infection in the birds; in this respect, the wet-mount method is arguably more subjective than culture techniques.
There is mounting evidence that diagnosing trichomonads by culture is more sensitive than wet-mount methods in detecting low-intensity infections (1, 2, 8), although the disparity in sensitivity between the methods varies. Other culture systems available for the diagnosis of Trichomonas species have been found to have sensitivities similar to that of the InPouch method (2, 4, 7), and PCR techniques have also been developed as alternative techniques (6, 9). However, despite the advantages of PCR methods (potentially faster than culture, and diagnosis is independent of parasite survival), it is rarely possible to use such techniques under field conditions, which is where most of the work on wild birds is carried out. It can be difficult to obtain the ingredients for other culture media, which may also be problematic to transport, require refrigeration, and still have a shorter shelf-life than the InPouch TF culture kits. This explains why the wet-mount method has been the only realistic diagnostic test in field conditions until recently. The advantages of the InPouch TF system for the diagnosis of T. gallinae in wild birds include convenience of sampling, ease of transport, relatively low cost, storage at room temperature, and a long shelf-life. Its greater expense over the wet-preparation method can be justified by these benefits together with its increased sensitivity and potentially lower subjectivity in diagnosing infections.
Avian trichomoniasis is becoming increasingly recognized in terms of the problems it causes for both conservation management of threatened species (in the threat it poses to immunologically naïve pigeons and doves), e.g., the pink pigeon and the Galapagos dove, and for game bird management, e.g., the mourning dove Zenaida macroura (there was a severe outbreak of the disease in the early 1950s [3]). Therefore, it is essential to use a screening method that is both accurate and suitable for use in the field. In conclusion, the higher sensitivity of the InPouch TF method compared to that of the wet preparation makes it an ideal tool for the diagnosis of T. gallinae infections in wild birds.
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Nancy Bunbury* Diana Bell School of Biological Sciences University of East Anglia Norwich, United Kingdom
Carl Jones
Andrew Greenwood
Paul Hunter
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