Edwin J. A. Veldhuizen

Usutu virus (USUV) is an arbovirus that circulates between mosquitoes and birds with occasional spillover events into non-avian species. USUV continues to circulate in the Netherlands, particularly in Eurasian blackbirds (Turdus merula), although other USUV-susceptible avian species have also been found. Current serosurveillance systems make use of serological methods that can detect anti-USUV antibodies in sera collected from live birds. However, they require a dedicated laboratory and rarely include serological analysis of deceased avian specimen. This study evaluates the use of a previously developed lateral flow microarray immunoassay (LMIA) to detect USUV non-structural 1 (NS1)-specific antibodies in blood clots and lung and liver tissue extracts collected from blackbird carcasses found in the Netherlands. The likelihood of detection of USUV NS1 antibodies in USUV RT-PCR-positive blackbirds was found to trend higher in lung tissue extracts. Additionally, the LMIA exhibited only minimal cross-reactivity between USUV NS1-specific antibodies and USUV NS1 and West Nile virus (WNV) NS1 capture antigens on the LMIA. This initial study demonstrates the feasibility of the LMIA to specifically detect USUV NS1 antibodies in lung tissue extracts of deceased blackbirds. In the future, a serological tool such as the one presented here, would allow for the rapid on-site analysis of both live and dead (avian) specimen found in the field.

The common avian origin of many zoonotic infections and epidemics warrants investigation into the mechanism of respiratory surface protection in reservoir species such as birds. Our recent molecular investigations on the evolution and pulmonary expression of an ancient family of proteins, the C-type lectins, have revealed unique molecular adaptations in the surfactant proteins avian SP-A1 (aSP-A1), aSP-A2 and aSP-C coupled with the loss of surfactant protein-D (SP-D) in the avian lineage. As surfactant proteins are members of the collectin family, a subgroup of the C-type lectins, an in silico search for related non-surfactant collectin proteins (Collectin-10 (CL-10) and Collectin-11 (CL-11)) in the NCBI genome database was conducted to understand their evolution in the avian lineage. In addition, both CL-10 and CL-11 gene expression in the lungs and other organs of zebra finches and turkeys was confirmed by PCR. These PCR-confirmed zebra finch and turkey CL-10 and CL-11 sequences were compared with sequenced and in silico -predicted vertebrate homologues to develop a phylogenetic tree. Compared with avian surfactant proteins, CL-10 and CL-11 are highly conserved among vertebrates, suggesting a critical role in development and innate immune protection. The conservation of CL-11 EPN and collagen domain motifs may compensate to some extent for the loss of SP-D in the avian lineage. This article is part of the theme issue ‘The biology of the avian respiratory system’.