West Nile Virus–related Trends in Avian Mortality in California, Usa, 2003–12

Abstract

ABSTRACT:West Nile virus (WNV) is an arbovirus transmitted enzootically by Culex mosquitoes among avian hosts. Since 2000, the California Dead Bird Surveillance Program (DBSP) has tracked avian mortality reported by the public on a telephone hotline and website and measured the prevalence of WNV infection in dead birds. We summarize herein WNV prevalence in dead birds tested and variation of WNV transmission over time and space with the use of DBSP data from 2003 to 2012. Prevalence among dead birds was highest in 2004, 2008, and 2012. This pattern was similar to peak WNV infection years for mosquitoes but not to human WNV incidence. Although American Crows (Corvus brachyrhynchos) were most frequently reported and tested, this species ranked third in infection prevalence (44%) after Yellow-billed Magpies (Pica nuttalli; 62%) and Western Scrub-Jays (Aphelocoma californica; 48%). Overall prevalence in American Robin (Turdus migratorius), House Finch (Haemorhous mexicanus), and House Sparrow (Passer domesticus) carcasses ranged from 18% to 22%. Corvid WNV prevalence was highest in South Coast, Bay/Delta, Sacramento, and San Joaquin valleys, and Klamath/North Coast bioregions, overlapping areas of elevated WNV activity in other surveillance measurements. Bioregional analysis revealed the avian species most likely to be reported and found positive in each bioregion. Our results may be useful to WNV surveillance and control efforts and provide insight into bird population trends in California.

The Role of Birds of Prey in West Nile Virus Epidemiology

“…WNV can also be transmitted by feeding on infected birds and other vertebrate hosts, such as reptiles, amphibians and mammals which are also susceptible to WNV and serve raptors and other birds either as prey or carrion [ 57 , 58 , 59 , 60 ]. Several species of birds (e.g., Great horned owl or American crow ( Corvus brachyrhynchos )) have experimentally proven their susceptibility via this mechanism [ 29 ].…”

Current Progress of Avian Vaccines Against West Nile Virus

“…Susceptibility of the avian population to the infection can vary depending on the species, being Corvidae (order Passeriformes) the most susceptible family [46][47][48], and important virus amplifiers [7][8][9], that play a key role in the epidemiology of the virus [10][11][12][13][14]. In fact, WNV epidemics in the US were associated with high crow mortality, driving to a significant decrease of native crow species [14][15][16][17]. According to the Centers for Disease Control and Prevention (CDC), birds from almost 300 different species have been found dead since 1999 in the US [49].…”

“…According to the Centers for Disease Control and Prevention (CDC), birds from almost 300 different species have been found dead since 1999 in the US [49]. This avian WNV-associated mortality has been reported around the world in domestic [50][51][52] and wild birds [11,17,53,54], including endangered species [55,56], as well as in ones adapted to human environments [16].…”

“…Hundreds of avian species have been reported as susceptible to WNV, particularly corvids (Corvidae), which can develop high levels of viremia [6,7], and are notable virus amplifiers [7-9], being, thus, important actors in the epidemiology of the virus [10][11][12][13][14]. Both domestic and wild avian species are susceptible to WNV infection and, in some cases, develop a WNV-associated disease that can lead to high mortality, as occurred during the US outbreak where crow populations declined alarmingly [14][15][16][17].Currently, there is no antiviral therapy against WNV, and the licensed vaccines are only for use in equids [1,18,19]. The availability of avian vaccines would benefit bird populations, both domestic (like farm birds and those grown for restocking and hunting activities) and wild ones (mainly endangered species housed in rehabilitation and wildlife reserves, and birds located at recreational facilities like zoos).…”

“…Hundreds of avian species have been reported as susceptible to WNV, particularly corvids (Corvidae), which can develop high levels of viremia [6,7], and are notable virus amplifiers [7-9], being, thus, important actors in the epidemiology of the virus [10][11][12][13][14]. Both domestic and wild avian species are susceptible to WNV infection and, in some cases, develop a WNV-associated disease that can lead to high mortality, as occurred during the US outbreak where crow populations declined alarmingly [14][15][16][17].…”