New outbreak of Bagaza virus in partridges in Spain and appearance in Portugal and in other birds

    Two studies analyze Bagaza virus outbreaks in birds that occurred for the second time in southern Spain in 2019 and for the first time in Portugal in 2021. The data confirm that the co-infection of this flavivirus and the parasite that causes malaria avian is the cause of the high mortality observed in the affected populations of red partridge.


    Flaviviruses are a genus of viruses whose transmission occurs mainly through mosquitoes. In the last decade, several of These flaviviruses have expanded their usual distribution, causing serious health problems in both human and animal medicine.. Some examples of emerging flaviviruses include the Zika virus, declared an international health emergency in 2016 by the World Health Organization (WHO); the Nile fever virus, of which 77 human cases were registered in Spain alone in 2020, 8 of which were fatal; and the Bagaza virus.

    The latter, the Bagasse virus, belongs to the Ntaya serocomplex and owes its name to the Bagaza district of the Republic of Central Africa, where it was first detected in 1966. In 2010, this African virus was detected for the first time in Europe, specifically in a region of southern Africa. Spain, as the cause of a high mortality outbreak that mainly affected the red-legged partridge (Alectoris rufa) and to a lesser extent pheasants.

     

    The populations of red partridge (Alectoris rufa) in southern Spain have already suffered two outbreaks of the Bagaza virus, both with high mortality rates, one in 2010 and the other in 2019 (Photo: Teresa Cardona Cabrera).

    The hypotheses formulated by the scientists of the Research Group in Health and Biotechnology (SaBio) of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM), along with researchers from the University of Córdoba, pointed to possible interactions between the virus and hemoparasites such as avian malaria (Plasmodium spp.), which are widely distributed globally and relatively common, are responsible for the high mortality rate of the Bagaza virus outbreak. However, Virus-parasite interactions during co-infections in the avian host have never been studied..

    The opportunity to investigate this matter arose in early October 2019, when it appeared a new viral outbreak with a high mortality rate that affected the red partridge population of a hunting farm, again in southern Spain. Many of the affected partridges were found dead, while others appeared weak, blind, with altered plumage and neurological symptoms (ataxia, lack of coordination or inability to fly). Some partridges were thin, but others had a normal body condition. Both the symptoms described and the geographical area affected coincided with the Bagaza virus outbreak in 2010..

    The study of this new Bagaza virus outbreak by the Sabio Group of IREC and the University of Córdoba has made it possible to identify, through the use of PCR techniques and their subsequent sequencing, the presence of both the Bagaza virus and the Plasmodium in samples taken from affected birds. Through immunohistochemistry it was possible to confirm the presence and co-localization of both pathogens (the Bagaza virus and the parasite Plasmodium) in the most serious lesions in organs such as the liver and spleen. This finding, together with the extent and severity of the lesions, suggests that both etiological agents contributed to the development of the clinical picture and its fatal outcome in the partridge populations affected by these outbreaks. On the other hand, the analyzes show that the Bagaza virus sequence detected in the 2019 outbreak differs from those recorded in the 2010 outbreak, which suggests the circulation of several strains or genotypes or a new introduction of the virus from the African continent.

     

    At the macroscopic level, the extent and severity of the lesions varied between animals, the large size and greenish coloration of the liver being especially striking. The microscopic study revealed lesions such as hyperemia, congestion and necrosis in most of the internal organs, but above all the presence in a very high number of one of the stages of development (phanerozoites) of a blood parasite inside the liver cells. .

    These two outbreaks of the Bagaza virus in Spain reveal The threat posed by emerging flaviviruses to wildlife. For example, the first outbreak in 2010 caused a remarkable impact on the abundance of natural populations of red partridge in the affected area, a species that is key to Mediterranean ecosystems and is an important economic engine for small game hunting.

    The recent detection of the first outbreak of the Bagaza virus in Portugal, where it has affected new bird species such as the wheatgrass (emberiza calandra) with a mortality similar to that observed in Spain, makes this virus a a growing threat to the wild birds of the Iberian Peninsula. The study that has addressed the analysis of this outbreak, carried out by various Portuguese institutions, such as CIBIO-InBIO, the University of Porto and the Estação Biológica de Mértola, in collaboration with the Sabio Group of IREC, allowed to elucidate two very important data that potentially will help to understand the factors involved in the development of viral foci: on the one hand, the virus detected in Portugal is highly similar to the virus that emerged in 2010 in southern Spain; on the other, the presence of the virus was also detected in samples taken from healthy captured birds, confirming its circulation.

     

    Transmission cycle of the Bagaza virus and the parasite Plasmodium spp. Both share mosquitoes as vectors. Direct transmission of Bagaza between partridges has been demonstrated under experimental conditions, but it is currently unknown whether it could affect mammals or humans in the same way as West Nile fever virus.

    The re-emergence of the virus in Spain and its appearance in Portugal, together with the co-infection with Plasmodium spp. and the high mortality it causes, show the need to investigate and better understand the relationship between these pathogens and the possible interactions between mosquitoes, which act as transmitters of both, and avian hosts.. The authors of these two research papers also highlight the urgency of revealing the possible external factors that may favor virus-parasite interaction, since this had not been previously observed.

    You can consult the scientific publications of these research works at: