An enzyme‐linked immunosorbent assay (Elisa) for the detection of chlamydial antibody in duck sera

Presence and shedding of Chlamydia psittaci in waterfowl in a rehabilitation facility and in the wild in New Zealand

AIMS

To determine the frequency of Chlamydia psittaci infection, shedding dynamics of C. psittaci, and C. psittaci genotype diversity in waterfowl temporarily resident in a rehabilitation facility and in mallards in the wild.

METHODS

Conjunctival-choanal-cloacal swabs were collected from apparently healthy captive wild mallards (Anas platyrhynchos; n = 114) and paradise shelducks (Tadorna variegata; n = 10) temporarily housed at a waterfowl breeding and rehabilitation facility (Wellington, NZ) and from wild mallards in Palmerston North (n = 50), and Southland (n = 50). DNA extracted from the swabs was analysed using quantitative PCR (qPCR) high-resolution melt curve (HRM) analysis, targeting the ompA gene of C. psittaci.

RESULTS

Of the captive waterfowl, 39/114 (34%) mallards and 6/10 (60%) paradise shelducks were positive for C. psittaci as were 24/100 (24%) wild mallards. All wild mallards and paradise shelducks carried only C. psittaci genotype C. In captive wild mallards, genotypes A and C, and a mixed infection of both genotypes were found. Captive wild mallards and paradise shelducks were found to be shedding 4 to 5 × 10⁴ and 1 × 10⁵ to 4 × 10⁵ copies of C. psittaci DNA per swab, respectively, with wild mallards shedding 4-677 DNA copies/swab.

CONCLUSIONS

Based on qPCR-HRM analysis, a high proportion of wild mallards were infected with C. psittaci but these birds were shedding only a small amount of bacterial DNA. The proportion of sampled ducks that were infected and the extent of bacterial shedding were higher in the birds in a wildlife rehabilitation facility. The major C. psittaci genotype found in the mallards and paradise shelducks was genotype C. This is the first detection of C. psittaci genotype A and co-infection of genotype A and C in ducks.

CLINICAL RELEVANCE

These results indicate that mallards are a reservoir of C. psittaci and therefore may pose a zoonotic risk to people involved in duck hunting, wildlife care and recreational duck feeding. Mallards may also pose a transmission risk to native birds, especially in captive facilities and this has conservation implications for the management of endangered native birds.

The application of the ELISA technique to the serology of chlamydiosis in goats: statistical evaluation of a method

The evaluation of the ELISA technique has been studied in the special case of its application to the serological diagnosis of chlamydiosis in goats. The results showed that this technique is reliable (accurate and reproducible) and efficient. Sera from 96 goats were studied with the ELISA technique, indirect immunofluorescence (IIF) and complement fixation (CF), the latter being the standard method in France. A comparison of the results revealed a similarity of findings with ELISA and indirect immunofluorescence and the greater sensitivity of the ELISA technique relative to that of complement fixation.

Analysis of caprine IgG1 and IgG2 subclass responses to Chlamydia psittaci infection and vaccination

Enzyme-linked immunosorbent assays (ELISAs) specific for caprine IgG(H+L), IgG1 and IgG2 were developed and evaluated for serodiagnosis of Chlamydia psittaci infections in a Tunisian goat flock with currently occurring chlamydial abortions and a clinically inapparent goat flock of an animal research facility. Additionally, ELISAs were applied to record the IgG1 and IgG2 dynamics of four goats vaccinated with inactivated Chlamydia psittaci and Coxiella burnetii. For screening purposes, the IgG(H+L) ELISA proved to be superior to the complement fixation test because it detected a larger number of chlamydial abortions and was easier to perform and to interpret. Analysis of Chlamydia psittaci-specific IgG1 and IgG2 responses to naturally occurring infections by ELISA revealed high IgG1 levels associated with IgG2 in goats with current abortions, whereas clinically inapparent, but seropositive goats were characterized by significantly lower IgG1 levels only (P less than 0.001). Similarly, the four vaccinated goats responded initially with Chlamydia psittaci-specific IgG1, whereas second and third vaccinations induced (as in goats with chlamydial abortions) predominantly IgG1, but also IgG2. The results indicated that clinically inapparent chlamydial infection may be distinguished from overt disease by analysing specific IgG1 and IgG2 responses. Applying Coxiella burnetii- specific ELISAs on field samples, IgG1 alone could be detected in eight, IgG2 alone in one and IgG1 combined with IgG2 in nine goats. The coxiella-specific antibody response of the four vaccinated goats was--in contrast to the chlamydia-specific response--characterized by IgG2 dominance.

Chlamydiosis in birds in Great Britain. 1. Serological reactions to chlamydia in birds sampled between 1974 and 1983

A total of 6593 serum samples from birds, received for diagnostic testing or surveys between 1974 and 1983, were titrated by direct complement fixation (CF) test against Chlamydia psittaci antigen. The percentage of positive reactions found was variable for domestic poultry, ranging from 1.5 in chickens to 22.2 in geese, and was highest in pigeons Columba livia (47.3) and collared doves Streptopelia decaocto (51.4). A moderate incidence was found for game birds (29.0), wild ducks (23.3) and imported birds of the order Psittaciformes (15.9). The highest titres were found in pigeons, collared doves and psittacines, confirming that infection is both frequent and active in these birds in Britain. Results of isolation of chlamydia from similar sources will be reported subsequently.