Investigating Infectious Deseases in the Spanisch Imperial Eagle

The Spanish Imperial eagle (Aquila adalberti) is the most threatened eagle in Europe. This species, endemic to the south-west of the Iberian Peninsula, has suffered a decline in the recent past, due to both the collapse of the populations of its staple prey, the European rabbit (from two viral diseases, myxomatosis and rabbit hemorrhagic disease), and direct and indirect persecution.

The remaining population is at present stable but fragmented and showing extremely reduced genetic variability. This could predispose these birds to the development of various pathologies, as the limited genetic variability could result in an impaired immune system. In fact, throughout the years, an unusual number of deaths of nestlings in the field has been found to be due to secondary opportunistic pathogens, especially in central Spain.

In addition, imperial eagles becoming disabled mostly from electrocution or trauma are being continuously monitored. Continuous stress from suffering lesions, treatment and captive environment has proven to be immunosuppressive.

For these reasons, the ECA is supporting a small scale epidemiologic study in order to investigate the prevalence of different pathogens among imperial eagles in the field and in captivity. The study involves the collection of samples during regular health checks in imperial eagles maintained in captivity, as well as in nestling and adult imperial eagles in the field, in after the capture (adults) of these for radio tagging or when these are banded and radio tagged at the nest (nestlings). Injured imperial eagles that are admitted to rehabilitation centres are also included in the study and are sampled upon admission if their physical condition allows it.

The obtained samples are tested by a combination of sophisticated laboratory methods (Polymerase Chain Reaction, PCR, culture, serology) for the presence of parasites, bacterial, fungal and viral pathogens. In addition studies on the exposure to spent lead ammunition, immune function and on the prevalence of antibodies are carried out.

To date these investigations have evidenced the exposure of Imperial eagles to most known avian pathogens, but most important is the detection of a Flavivirus, West-Nile virus. This virus has proven to be both, the culprit of primary disease and death, and also of the appearance of severe disease due to pathogens that do not necessarily cause diseases in a healthy eagle.

West Nile virus is in Europe traditionally a non-pathogenic virus in birds that cycles between these and mosquitoes with sporadic infections of horses and humans. However after its introduction into North America this virus has caused disease and death in persons, horses and thousands of native birds leading to the decline of some native species such as the American robin. Further investigations into the role of this virus and other pathogens may reveal important information with view to conservation of the Spanish imperial Eagle and other species.

From each eagle complete morphometry and samples for haematology, microbiology etc. are obtained exerting great care not to harm the birds and reducing stressful procedures as much as possible. Photos © R. Sanchez