Date Published: June 21, 2006
Publisher: BioMed Central
Author(s): Morten Tryland, Kjell Handeland, Anna-Marie Bratberg, Inge-Tom Solbakk, Antti Oksanen.
To assist in evaluating serological test results from dead animals, 10 silver foxes (Vulpes vulpes) and 10 blue foxes (Alopex lagopus), 6 of each species previously vaccinated against and all challenged with Microsporum canis, were blood sampled and euthanased. Fox carcasses were stored at +10°C, and autopsy was performed on Days 0, 2, 4, 7, and 11 post mortem during which samples from blood and/or body fluid from the thoracic cavity were collected. Antibodies against M. canis were measured in an enzyme-linked immunosorbent assay (ELISA) as absorbance values (optical density; OD). To assess the degradation of antibodies, the ratio between post mortem and ante mortem absorbance was calculated. The mean absorbance from samples collected during autopsy was generally lower than from samples from live animals. In blood samples, this difference increased significantly with time (P = 0.04), while in body fluid samples the difference decreased (not significant; P = 0.18). We suggest that a positive serological result from testing blood or body fluid of a dead animal may be regarded as valuable, although specific prevalences obtained by screening populations based on this type of material may represent an under-estimation of the true antibody prevalence. Negative serological test results based on material from carcasses may be less conclusive, taken into account the general degradation processes in decaying carcasses, also involving immunoglobulin proteins.
Wild animal carcasses obtained for autopsy frequently are in an advanced stage of post mortem decomposition, which complicates morphological evaluation and impairs the possibility of making a proper diagnosis . In addition to morphological examination, the wildlife pathologist may also utilise various tests, such as isolation of the infectious agent, detection of antigen in tissues by immunohistochemistry or polymerase chain reaction [2,3]. Also serological tests based on the demonstration of specific antibodies against various infective agents are performed on dead animals [4-6]. Thus, a systematic use of serological tests on autopsy material may give valuable information on the presence of specific infections in wildlife populations. The speed of post mortem decomposition of carcasses is affected by the ambient temperature, the higher the temperature, the faster the breakdown. The fate of immunoglobulins in decomposing carcasses is not well known, but obviously it will be subjected to decomposition as other proteins and organic matter. Systematic studies on the availability of blood and tissue fluids and their usability for serological testing during post mortem decomposition are missing. The present work was carried out to study the persistence of antibodies specific for the dermatophyte Microsporum canis in fox carcasses examined at different stages of post mortem decomposition.