Bagaza virus and Plasmodium spp. coinfection in red-legged partridges (Alectoris rufa), in Southern Spain 2019

Dynamics of Bagaza, West Nile, and Usutu Viruses in Red-Legged Partridges, Portugal, 2018-2022

Long-term serologic surveillance of red-legged partridges suggests emergence of Bagaza virus in Portugal in 2021, associated with disease outbreaks in this species. Results also reveal sporadic circulation of Usutu virus and endemic circulation of West Nile virus, highlighting the role of red-legged partridges in the transmission and maintenance cycle and as sentinels of orthoflaviviruses.

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

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.

Re-emergence of Bagaza virus in wild birds from southern Spain

Bagaza virus (BAGV; Orthoflavivirus bagazaense) is an emerging vector-borne flavivirus affecting avian species with severe implications for animal health, and whose zoonotic potential has also been suggested. The aim of the present study was to monitor the epidemic outbreak of BAGV in wild birds from Spain in 2021. BAGV cases were confirmed in game bird species, including red-legged partridges (Alectoris rufa) and common pheasants (Phasianus colchicus) from 24 hunting areas. Suspected cases (clinical signs and/or mortality compatible with BAGV infection but without molecular confirmation) were also detected in 11 additional hunting areas. The outbreaks showed a seasonality mainly restricted to July and August. Estimated morbidity [25.8 % (95 %CI: 11.3-40.3) in partridges and 8.7 % (95 %CI: 0.0-18.0) in pheasants] and mortality rates [27.3 % (95 %CI: 12.5-42.1) in partridges and 13.0 % (95 %CI: 1.9-24.1) in pheasants] were found in the affected hunting areas. In addition, 215 non-game birds belonging to 46 different species were sampled by passive surveillance upon admittance to rehabilitation centres during 2021. BAGV infection was detected for the first time in green woodpecker (Picus viridis), spoonbill (Platalea leucorodia), white stork (Ciconia ciconia) and cynereous vulture (Aegypius monachus), expanding the host range of this emerging pathogen. In contrast to other species, game birds showed distinct BAGV related lesions, primarily myocarditis and encephalitis in addition to inflammatory infiltrates and necrosis in the liver and kidney. Molecular analyses revealed a homology of 97.4-98.0 % and 92.5-92.7 % between the BAGV sequences obtained in the present study (492 bp) and those isolated in 2010 and 2019 in southern Spain, respectively. These results allow to hypothesise about the likely silent and endemic circulation of BAGV since 2010 in this European region, although repeated virus reintroduction from neighbouring territories cannot be ruled out. Our findings evidence the sanitary, ecological and conservation implications of the re-emerged BAGV for wild birds, also emphasising the need to increase surveillance for monitoring and early detection of flavivirus dynamics in high-risk areas.

Indirect interaction between an endemic and an invading pathogen: A case study of Plasmodium and Usutu virus dynamics in a shared bird host population

Infectious disease agents can influence each other's dynamics in shared host populations. We consider such influence for two mosquito-borne infections where one pathogen is endemic at the time that a second pathogen invades. We regard a setting where the vector has a bias towards biting host individuals infected with the endemic pathogen and where there is a cost to co-infected hosts. As a motivating case study, we regard Plasmodium spp., that cause avian malaria, as the endemic pathogen, and Usutu virus (USUV) as the invading pathogen. Hosts with malaria attract more mosquitoes compared to susceptible hosts, a phenomenon named vector bias. The possible trade-off between the vector-bias effect and the co-infection mortality is studied using a compartmental epidemic model. We focus first on the basic reproduction number R0 for Usutu virus invading into a malaria-endemic population, and then explore the long-term dynamics of both pathogens once Usutu virus has become established. We find that the vector bias facilitates the introduction of malaria into a susceptible population, as well as the introduction of Usutu in a malaria-endemic population. In the long term, however, both a vector bias and co-infection mortality lead to a decrease in the number of individuals infected with either pathogen, suggesting that avian malaria is unlikely to be a promoter of Usutu invasion. This proposed approach is general and allows for new insights into other negative associations between endemic and invading vector-borne pathogens.

Accelerating targeted mosquito control efforts through mobile West Nile virus detection

BACKGROUND

Different mosquito control strategies have been implemented to mitigate or prevent mosquito-related public health situations. Modern mosquito control largely relies on multiple approaches, including targeted, specific treatments. Given this, it is becoming increasingly important to supplement these activities with rapid and mobile diagnostic capacities for mosquito-borne diseases. We aimed to create and test the applicability of a rapid diagnostic system for West Nile virus that can be used under field conditions.

METHODS

In this pilot study, various types of adult mosquito traps were applied within the regular mosquito monitoring activity framework for mosquito control. Then, the captured specimens were used for the detection of West Nile virus RNA under field conditions with a portable qRT-PCR approach within 3-4 h. Then, positive samples were subjected to confirmatory RT-PCR or NGS sequencing in the laboratory to obtain genome information of the virus. We implemented phylogenetic analysis to characterize circulating strains.

RESULTS

A total of 356 mosquito individuals representing 7 species were processed in 54 pools, each containing up to 20 individuals. These pools were tested for the presence of West Nile virus, and two pools tested positive, containing specimens from the Culex pipiens and Anopheles atroparvus mosquito species. As a result of subsequent sequencing, we present the complete genome of West Nile virus and Bagaza virus.

CONCLUSIONS

The rapid identification of infected mosquitoes is the most important component of quick response adulticide or larvicide treatments to prevent human cases. The conceptual framework of real-time surveillance can be optimized for other pathogens and situations not only in relation to West Nile virus. We present an early warning system for mosquito-borne diseases and demonstrate its application to aid rapid-response mosquito control actions.

First identification and molecular subtyping of Blastocystis in free-living wild birds from urban Xinxiang, China

Blastocystis is a common enteric protist infecting humans, domestic animals, and wildlife worldwide. However, data on the prevalence and subtype diversity of Blastocystis in free-living wild birds in urban districts are rare. In this study, a total of 138 fresh fecal samples from free-living wild birds were collected from three universities and three communities in Xinxiang, China, to explore the infection rate, Blastocystis subtypes present and zoonotic potential of this protist. Blastocystis presence was determined with nested-PCR amplification based on the partial small ribosomal subunit (SSU rRNA) gene. Presence was detected from one community (Wupu) at an overall rate of 1.5% (2/136). Further DNA sequencing and phylogenetic analyses identified two ruminant-associated subtypes, ST10 (n = 1) and ST24 (n = 1), implying a cross-species transmission of Blastocystis from ruminants. This is the first report on the infection of ST10 and ST24 in free-living wild birds in an urban area in China. As potentially zoonotic subtypes, the occurrence of ST10 and ST24 suggests that these free-living birds could play a role in spreading Blastocystis to humans in Xinxiang.