Nicole M. Nemeth

NATURAL AND EXPERIMENTAL WEST NILE VIRUS INFECTION IN FIVE RAPTOR SPECIES

We studied the effects of natural and/or experimental infections of West Nile virus (WNV) in five raptor species from July 2002 to March 2004, including American kestrels (Falco sparverius), golden eagles (Aquila chrysaetos), red-tailed hawks (Buteo jamaicensis), barn owls (Tyto alba), and great horned owls (Bubo virginianus). Birds were infected per mosquito bite, per os, or percutaneously by needle. Many experimentally infected birds developed mosquito-infectious levels of viremia (>105 WNV plaque forming units per ml serum) within5 days postinoculation (DPI), and/or shed virus per os or per cloaca. Infection of organs 15–27 days postinoculation was infrequently detected by virus isolation from spleen, kidney, skin, heart, brain, and eye in convalescent birds. Histopathologic findings varied among species and by method of infection. The most common histopathologic lesions were subacute myocarditis and encephalitis. Several birds had a more acute, severe disease condition represented by arteritis and associated with tissue degeneration and necrosis. This study demonstrates that raptor species vary in their response to WNV infection and that several modes of exposure (e.g., oral) may result in infection. Wildlife managers should recognize that, although many WNV infections are sublethal to raptors, subacute lesions could potentially reduce viability of populations. We recommend that raptor handlers consider raptors as a potential source of WNV contamination due to oral and cloacal shedding.

Persistent West Nile virus infection in the house sparrow (Passer domesticus)

Long-term persistence of West Nile virus (WNV) infection within vertebrate reservoir hosts is a potential mechanism for overwintering of this (and other) arbovirus(es) at temperate latitudes. The house sparrow (Passer domesticus), an established amplifying host for WNV and other arboviruses, was used as a model to confirm chronicity of WNV infection in passerine birds and to evaluate the feasibility of two overwintering mechanisms: blood-borne infection of arthropod vectors (recrudescence) and oral infection of vertebrate reservoir hosts (ingestion of infected tissues through predation). WNV-inoculated sparrows were monitored for persistent infection for up to 2xa0years. Infectious virus persisted in tissues through 43xa0days, but not in sera beyond 6xa0days. Viral RNA persisted in tissues through 65xa0days. Chronicity of WNV infection in some tissues, but not blood, supports the predation mechanism of WNV overwintering, but not recrudescence. RNA persistence impacts interpretation and etiologic determination of avian mortality.

Response of a Scarlet Macaw Ara macao population to conservation practices in Costa Rica

Summary The Central Pacific Conservation Area contains one of Costa Rica’s two viable, but threatened Scarlet Macaw Ara macao populations. For 14 years (1990–2003), we monitored the size of this population. Non-linear models fitted to 1990–1994 observations revealed seasonal and longterm changes in population size. The peak of annual population size occurred in August, with a cyclic range of about 90 birds between the lowest and highest points of the annual cycle. The best model also revealed a decline in population size of approximately eight birds counted per year or 4% of the total population per year (1990–1994). Young-to-adult ratios calculated for the month of August during this study fluctuated around a baseline that averaged 6.1% a year (1990–2003). These ratios exceeded 8% for three different years (1995, 1996 and 2000). All three of these “good” recruitment years occurred after management began, and two of them were associated with zealous anti-poaching efforts that ultimately could not be sustained. After intensive management practices began in 1995, the August counts increased by about 37 individuals in two years (1995–1996) to an average 243 individuals, which remained almost constant up to 2003. Management practices included creation of a local conservation organization that coordinated environmental education, artificial nest construction, networking among stakeholders and with governmental authorities, and artificial and natural nest protection. Although Scarlet Macaw conservation efforts have been inconsistent since 1997, our study demonstrates that collaborative conservation by local stakeholders increased the population of this threatened species in 1995–1996, and from 1996 to present the population has sustained itself.

Cross-Protection Between West Nile and Japanese Encephalitis Viruses in Red-Winged Blackbirds (Agelaius phoeniceus)

Abstract Similar to West Nile virus (WNV), Japanese encephalitis virus (JEV) has a history of intercontinental spread, and birds are important for the maintenance and transmission of both of these closely related viruses. We examined viremic and serologic responses of blackbirds (Agelaius phoeniceus), with and without immunity to WNV, following experimental inoculation with two strains of JEV. Japanese encephalitis (JE) viremia was detected in only one of 16 (6.3%) WNV-immune birds, while all 16 nonimmune birds had detectable JE viremia. Two weeks after JEV inoculation, all birds without pre-existing WNV immunity had clearly distinguishable anti-JEV antibodies, while in all birds with pre-existing WNV immunity, antibodies to WNV and JEV were either indistinguishable or the anti-WNV antibody titers were significantly higher. As WNV is endemic throughout much of North America, WNV immunity among birds may dampen transmission while complicating the serologic diagnosis of JEV, should this pathogen be introduced to North America.

Comparison of Argentinean Saint Louis Encephalitis Virus Non-Epidemic and Epidemic Strain Infections in an Avian Model

St. Louis encephalitis virus (SLEV, Flavivirus, Flaviviridae) is an emerging mosquito-borne pathogen in South America, with human SLEV encephalitis cases reported in Argentina and Brazil. Genotype III strains of SLEV were isolated from Culex quinquefasciatus mosquitoes in Cordoba, Argentina in 2005, during the largest SLEV outbreak ever reported in South America. The present study tested the hypothesis that the recent, epidemic SLEV strain exhibits greater virulence in birds as compared with a non-epidemic genotype III strain isolated from mosquitoes in Santa Fe Province 27 years earlier. The observed differences in infection parameters between adult House sparrows (Passer domesticus) that were needle-inoculated with either the epidemic or historic SLEV strain were not statistically significant. However, only the House sparrows that were infected with the epidemic strain achieved infectious-level viremia titers sufficient to infect Cx. spp. mosquitoes vectors. Furthermore, the vertebrate reservoir competence index values indicated an approximately 3-fold increase in amplification potential of House sparrows infected with the epidemic strain when pre-existing flavivirus-reactive antibodies were present, suggesting the possibility that antibody-dependent enhancement may increase the risk of avian-amplified transmission of SLEV in South America.

Clinical and acquired immunologic responses to West Nile virus infection of domestic chickens (Gallus gallus domesticus)

Numerous bird species are highly susceptible to North American strains of West Nile virus (WNV), and although domestic chickens are relatively resistant to WNV-associated disease, this species currently represents the most practical avian model for immune responses to WNV infection. Knowledge of the immunomodulation of susceptibility to WNV in birds is important for understanding taxonomic differences in infection outcomes. While focusing on immunophenotyping of CD3(+), CD4(+), CD8(+), and CD45(+) lymphocyte subpopulations, we compared lymphocyte subpopulations, blood chemistries, cloacal temperatures, IgM and IgG antibody titers, and differential whole-blood cell counts of WNV-infected and uninfected hens. Total blood calcium and lymphocyte numbers were lower in WNV-infected chickens compared with uninfected chickens. The heterophil-to-lymphocyte ratio increased over time from 2 to 22 d postinoculation (DPI) in uninfected chickens and from 2 to 8 DPI in WNV-infected chickens, although levels declined from 8 to 22 DPI in the latter group. No significant differences were found in the remaining immunological and hematological variables of the WNV-infected and uninfected groups. Our results reaffirm that chickens are resistant to WNV infection, and demonstrated that the heterophil-to-lymphocyte ratio differed between groups, allowing for sorting of infection status. Similar patterns in immune responses over time in both infected and uninfected hens may be related to age (i.e., 10 wk) and associated immune development.

Serosurveillance for Japanese encephalitis and West Nile viruses in resident birds in Hawai'i.

Japanese encephalitis virus (JEV) and West Nile virus (WNV) are emerging zoonotic arboviruses that have recently undergone intercontinental expansion. Both JEV and WNV are naturally transmitted between mosquito vectors and vertebrate reservoir hosts, including birds. A potential route of JEV introduction from Asia to western North America is via the Hawaiian archipelago, while the spread of WNV from mainland North America to Hawai‘i is also considered an impending threat. We surveyed resident, non-native bird sera for antibodies to JEV and WNV on two Hawaiian Islands from 2004–2005. Three of 1,835 birds (0.16%) had evidence of antiflavivirus antibodies, demonstrating neutralizing activity to JEV and St. Louis encephalitis virus (SLEV). These detections could represent a limited transmission focus of either, or both, JEV and SLEV, or cross-reactive antibodies due to primary infection with an alternate flavivirus. Frequent air traffic from both Asia and North America to Hawai‘i, along with the presence of probable competent vectors and amplifying vertebrate hosts in Hawai‘i, increases the likelihood of introduction and maintenance of novel flaviviruses. Therefore, it is important to monitor for the presence of these viruses.

Prevalence of antibodies to West Nile virus and other arboviruses among Crested Caracaras (Caracara cheriway) in Florida.

We documented the antibody prevalence to three arboviruses, St. Louis encephalitis virus (SLEV), eastern equine encephalitis virus (EEEV), and West Nile virus (WNV), in Crested Caracaras (Caracara cheriway; n=80) in Florida from 2007 to 2008. Antibody prevalence to WNV was higher (9%) than for the other viruses. Most seropositive birds were adults (≥3 yr of age), with 55% of adults testing positive for antibodies to at least one virus. Adults were significantly more likely to have antibodies to WNV than nonadults (P<0.001). Prevalence of SLEV and EEEV antibodies among Crested Caracaras was 3% for each virus, and three adult caracaras had indistinguishable anti-flavivirus antibodies. The susceptibility of Crested Caracaras to adverse effects of WNV, SLEV, or EEEV infection remains unknown; however, we observed that some free-ranging individuals survived infection and successfully fledged young. Knowledge of arboviral infection among Florida’s Crested Caracara, which is both state and federally threatened, is valuable considering increasing pressure on this population from rapid and extensive habitat alterations.

Experimental Exposure of Swallow Bugs (Hemiptera: Cimicidae) to West Nile Virus

ABSTRACT The cliff swallow (Petrochelidon pyrrhonota, Vieillot) could potentially play an important role in the transmission of West Nile virus (WNV) because of its breeding ecology, reservoir competence status, and potentially high natural exposure rates. These birds nest in colonies and their nests are occupied year round by swallow bugs (Oeciacus vicarius, Hovarth), hematophagus ectoparasites that feed primarily on cliff swallows. Swallow bugs are most likely exposed to WNV while feeding on infectious blood of cliff swallows and, thus, if competent vectors, could contribute to initiation and maintenance of seasonal WNV transmission. In addition, swallow bugs remain within nests year round and, therefore, if persistently infected and competent vectors, they could provide an overwintering mechanism for WNV. We tested the hypothesis that swallow bugs become infected with WNV through direct abdominal inoculation or ingestion of infectious blood meals. We observed that swallow bugs did not maintain or amplify WNV, and infectious virus titers within bugs declined over 15 d postexposure. These results suggest that swallow bugs may not be competent vectors of WNV, and therefore are unlikely to play a significant role in transmission.