Migratory Birds and the Dispersal of Arboviruses in California

Abstract

MATERIALS AND METHODS Bird collections.Migratory and resident birds were captured while transiting sites on the northeastern (35.51, −115.92) and northwestern (33.46, −116.06) shores of the Salton Sea, Coachella Valley, Riverside County, CA, from 1996 through 2005. In addition, migratory transients were targeted during collections made during the springs of 2006 and 2007. Migrants and other birds also were collected during 1996 through 2008 in Kern County, primarily from wetlands at the Kern National Wildlife Refuge (35.73,) and the Kern River (35.32,. The ecology of these areas, descriptions of arbovirus activity, and bird sampling methods have been described previously. 20,23 Briefly, birds were collected using multiple mist nets and grain-baited traps. Mist nets were 10 m long × 2.5 m tall and had 28-, 32-, or 60-mm mesh depending on the target species. Captured birds were banded with U.S. Geological Survey (USGS) bands, aged, sexed, and a 0.1 mL sample of blood collected from the jugular vein with 28-g needles. For antibody detection, blood samples were expelled into 0.9 mL of 0.9% saline solution, clarified through centrifugation, and stored at −70°C. During 2004During , 2006During , and 2007 blood samples from migratory species collected in Coachella Valley were expelled into 0.4 mL of virus diluent (phosphate buffered saline, 15% fetal bovine sera, antibiotics) and tested for infectious virus and antibody. Data from the California WNV Dead Bird Surveillance Program 24 on neotropical migrants that were found dead by the public, sent for necropsy, and tested positive for WNV RNA were included for comparison.Experimental infection. Abstract. Each spring large numbers of neotropical migrants traversing the Pacific flyway pass through the Coachella Valley enroute to northern destinations, providing an opportunity to test the hypothesis that mosquito-borne encephalitis viruses are introduced annually into California by migratory birds. A total of 5,632 sera were collected from 43 species of migrants during spring (April-June), of which 34 (0.61%) comprised of 14 species tested positive by enzyme immunoassay; only 10 were confirmed by plaque reduction neutralization tests (PRNT). In addition, of 1,109 migrants comprised of 76 species that were reported dead by the public and necropsied, 126 (11%) were positive for West Nile virus (WNV) RNA; however, only three (0.7%) of 428 birds tested during the spring were positive. Limited experimental infection studies with WNV showed that Orange-crowned Warblers were highly susceptible and frequently died, whereas most Yellow Warblers survived. Our results indicated that birds entering California rarely exhibited a history of infection and that most birds probably became infected after entering California.

Reemergence of St. Louis Encephalitis Virus, California, 2015

“…A similar ancestral topology of Brazil and Peru strains from the 1970s to the 2003 California isolate also suggests movement from South to North America. The Salton Sea and associated habitats possess diverse avifauna and may serve as a resting point for SLEV-infected migratory birds that traverse the Pacific flyway ( 13 ). Alternately, SLEV may have come from elsewhere in the United States after being introduced from South or Central America, but sequences from US states reporting SLEV activity in recent years are not publicly available.…”

West Nile virus: A re-emerging pathogen revisited

“…A primary role of migratory birds in WNV introduction, reintroduction, and spread across Europe [135][136][137][138][139] and the Americas [140,141] is well documented. However, comparison of the levels of neutralizing antibodies in migratory and resident birds in the south of Spain [135,136] , the seroconversion observed in some recaptured resident birds of the same area [137] , and the significant number of positive resident birds found in Great Britain [142] and Italy [143] support that there is also local circulation of the virus.…”

Terrestrial Bird Migration and West Nile Virus Circulation, United States

“…Because birds are the primary reservoirs for WNV, this finding was not surprising, but it is relevant because bird migration has also been implicated in the movement of influenza A virus ( 13 ), Borrelia burgdorferi (Lyme disease agent) ( 14 ), other pathogenic organisms ( 1 ), and even invasive invertebrate organisms ( 15 ). Several serologic studies (e.g., ELISA, plaque reduction neutralization test) have been used to determine the direction of WNV movement within the Atlantic, Mississippi, and Pacific flyways and demonstrated WNV in birds migrating southward, whereas evidence of the virus in birds during northward migration is limited ( 16 , 17 ). …”