Abstract

Over the past 2 years on the islands of Fuerteventura and Lanzarote in the Canary Islands off the west coast of Africa, ongoing ecological studies of desert passerines have uncovered the occurrence of an apparent epidemic of health problems in two species: the short-toed lark, Calandrella rufescens, and Berthelot’s pipit, Anthus berthelotii. Two other native passerine species which are found in the same steppe habitats associated with dairy goat farming, the Spanish sparrow, Passer hispaniolensis and the trumpeter finch, Bucanetes githagineus, have been studied simultaneously. Over 800 birds from the four species have been trapped and ringed over the past 2 years in April, July and November. Of 465 individuals from the two affected species studied over the various collection periods, 28% to 49% (mean 42.5%) of the birds had clinically obvious pox-like lesions involving the legs, feet and, occasionally face. Of a similar number of trumpeter finches and sparrows trapped at the same locations at the same time, none showed evidence of infection. Histopathology and electron microscopy have confirmed the presence of poxvirus in the lesions, whereas serology using standard, fowl and pigeon poxvirus-based diagnostic agar gel immunodiffusion techniques yielded negative results. Serology was not diagnostic in this case because of the limited (74.6%, pipit; 74.9% lark) similarity between the viruses in our species and fowlpox virus on which the serologic tests are based. Using a 575 base pair DNA fragment from the 4b core gene of a fowlpox virus strain, the virus isolated from dried lesions of C. rufescens has only 80.5% similarity with the virus isolated from A. berthelotii, and 91.3% similarity with canarypox, whereas A. berthelotii poxvirus has 80% similarity with canarypox, which indicates that these are two distinct and possibly new avian poxviruses.

The conservation implications of this epidemic of avian pox among birds in the Canary Islands are considerable. We have discovered a high prevalence of disease similar to that described in well-studied, native passerines in Hawaii that are known to be threatened, endangered, or even extinct, at least in part due to poxvirus infection. Of the species we have studied, all except the sparrow are designated threatened. Other globally endangered species exist in the same habitats in the Canary Islands of Fuerteventura and Lanzarote, such as the houbara bustard, Chlamydotis undulata, and the stone curlew, Burhinus oedicnemus. Subspecies of these birds on the mainland have been diagnosed with poxvirus infections. It will be essential to investigate environmental and biologic factors that are contributing to the increased disease susceptibility of these isolated populations of vulnerable bird species, in order to reverse this alarming trend in disease occurrence.