# Weak association of Usutu virus and haemosporidian infection in birds collected in Germany

## TL;DR

This study examines the relationship between Usutu virus and haemosporidian infections in German birds, finding a weak association between the two pathogens.

## Contribution

The study provides new insights into the co-occurrence patterns of Usutu virus and haemosporidians in wild bird populations in Germany.

## Key findings

- The prevalence of Usutu virus peaked in 2018 and then declined consistently.
- Haemosporidian prevalence initially declined but increased later, showing an inverse trend to Usutu virus.
- A weak positive association between the two pathogens was found in 2020 and across all years combined.

## Abstract

The Usutu Virus (USUV) is a mosquito-borne flavivirus originated in Africa. The virus circulates in Germany since 2010. It is primarily transmitted and maintained in the natural cycle by Culex mosquitoes and primarily affects birds, particularly Eurasian blackbird (Turdus merula), leading to significant mortality. Several studies have reported a high co-infection rate of European birds with both USUV and haemosporidians. Haemosporidians are blood parasites which maintain an enzootic life cycle with birds via different arthropod vectors. This study conducted screenings of birds from Germany received through a citizen's science project for both, USUV and haemosporidians between 2016 and 2021. The prevalence of USUV reached its peak in 2018, when it was first detected throughout most parts of Germany rather than being limited to localised hotspots. Subsequently, USUV prevalence consistently declined. On the other hand, the prevalence of haemosporidians initially declined between 2016 and 2019, but experienced a subsequent increase in the following years, exhibiting a more or less inverse pattern compared to the prevalence of USUV. In 2020, a statistically significant positive association between both pathogens was found, which was also detected across all years combined, indicating if at all a weak relationship between these pathogens.