Browsing by Subject "avian influenza"
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Item Ecological and Molecular Characterization of Avian Influenza Viruses Obtained from Waterfowl on the Texas Coast(2011-10-21) Ferro, Pamela JoyceWe collected 6,823 cloacal swabs over four years (2005?2006: 1,460; 2006? 2007: 2,171; 2007?2008: 2,424; and 2008?2009: 768) from 30 potential avian host species. Most samples (88.3 percent) were from dabbling ducks (genus Anas), while diving ducks (genus Aythya) accounted for 5.0 percent, and geese (genera Anser, Chen, and Branta) 3.0 percent of the samples tested. Waterfowl (Anatidae) comprised 98.7 percent of samples, with 1.8 percent from non-migratory dabbling ducks (genus Anas). All samples were screened for avian influenza virus (AIV) by AIV-matrix real-time RT-PCR (rRT-PCR); all rRT-PCR positive samples (541) were processed for virus isolation as well as 4,473 rRT-PCR negative samples. Differences were observed in apparent prevalence estimates over the four years between virus isolation (0.5, 1.3, 3.9, and 0.7 percent) and rRT-PCR (5.9, 6.5, 11.2, and 5.5 percent). We isolated 138 AIVs, of which two were obtained from rRT-PCR negative samples. Unlike previous reports of seasonal variation in AIV prevalence, we documented differences in prevalence estimates among months using rRT-PCR only during 2008?2009 and by virus isolation only during 2006?2007 and 2007?2008. Several of the AIV subtypes we identified are common in North America (e.g., H3, H4, and H6); H3N8 and H4N6 were the most common subtype combinations isolated. Similar to most surveillance studies, we found no significant difference in AIV infection based on host sex, but did find that juveniles were more likely to be positive for AIV than adults. We also documented that dabbling ducks were more likely to be positive for AIV than diving ducks, although not all dabbling ducks are equally likely to be positive. Molecular sequence analysis revealed no insertions of multiple basic amino acids at the cleavage site, which supported the identification of low pathogenic AIV. Phylogenetic anlyses performed on H5, H6, H7, N1, N2, N3, and N4 subtypes sequenced indicated similarity to other North American isolates with the exception of seven H6 which were more similar in amino acid translation to an isolate from Japan. In sum, this is the first multiyear study of avian influenza viruses on waterfowl wintering grounds of the Central Flyway, a historically understudied area of North America.Item Epidemiologic and Economic Analysis of Avian Influenza in Nepal(2013-08-05) Karki, SurendraMany countries, including Nepal, have been affected with highly pathogenic avian influenza (HPAI) outbreaks. There have been human mortalities in some countries and large numbers of poultry either died or were culled due to HPAI. The overall objective of this thesis was to improve our understanding of the epidemiology and economics of avian influenza (AI), and particularly HPAI, in Nepal. We determined the seroprevalence of and risk factors for AI virus antibodies presence in ducks in Kathmandu, Nepal. The estimated true prevalence of AI viruses (AIV) antibodies was 27.2% [95% Confidence Interval (CI): 24.6- 29.5]. Age of the ducks was identified as the only risk factor for AIV seropositivity. Ducks older than one year were more likely to be seropositive compared to ducks less than six months of age [Odds Ratio= 2.17 (95% CI: 1.07- 4.39)]. This study provided baseline information about seroprevalence of AIVs in Kathmandu that will benefit further research to differentiate the subtypes of AIVs circulating in Kathmandu. We also evaluated alternatives to the current control program (CCP) for HPAI in Nepal. The considered alternatives were: (i) absence of control measures (ACM) and (ii) vaccinating 60% of the domestic poultry flock twice per year. Cost-benefit analysis approach was used to evaluate the economic feasibility of the programs. In terms of the benefit-cost ratio, our findings indicated that there is a return of 1.96 dollars for every dollar spent in the CCP compared to ACM. The net present value of the CCP versus ACM was US$ 989,918. The vaccination program yielded a return of 2.41 dollars for every dollar spent when compared to the CCP. The net present value of vaccination versus implementing the CCP was US$ 13,745,454. These results support a continued investment into the CCP rather than ceasing to implement government regulated control measures and suggest that vaccination may be an even better control alternative. In summary, our studies have highlighted the value of epidemiologic and economic analysis in research of AI. Our results are expected to lead to an improved understanding and awareness of AI in Nepal and to formulation of better control strategies.Item Evaluation of Sindbis-M2e Virus Vector as a Universal Influenza A Vaccine(2012-10-19) Vuong, ChristineAlthough avian influenza virus (AIV) infections in domestic poultry are uncommon, transmission of avian influenza from wild waterfowl reservoirs does occur. Depopulation of the infected flock is the typical response to AIV outbreaks in domestic chicken production, causing a loss in profits and accumulation of unexpected expenses. Because it is impossible to know which of many virus subtypes will cause an outbreak, it is not feasible for the U.S. to stockpile vaccines against all possible avian influenza threats. Currently, the U.S. does not routinely vaccinate chickens against influenza due to the inability to differentiate infected from vaccinated animals (DIVA), which would place limitations on its trade markets. A Sindbis virus vector expressing the PR8 influenza strain's M2e peptide was developed as a potential universal DIVA vaccine. M2e is a conserved peptide amongst influenza A viruses; M2e-specific antibodies induce antibody-dependent cytotoxicity or phagocytosis of infected cells, reducing production and shedding of AIV during infection. In this study, chickens were vaccinated at one-month-of-age with parental (E2S1) or recombinant Sindbis viruses expressing the PR8 M2e peptide (E2S1-M2e) by subcutaneous or intranasal routes at high (106 pfu) or low (103 pfu) dosages. Chickens were boosted at 2-weeks post-initial vaccination using the same virus, route, and dosage, then challenged with low pathogenic H5N3 AIV at 0.2 mL of 106/mL EID50 2-weeks post-boost. Serum samples were collected at 1-week and 2-weeks post-vaccination, 2-weeks post-boost, and 2-weeks post-challenge and screened for PR8 M2e-specific IgY antibody production by ELISA. Both high and low dose subcutaneously, as well as high dose intranasally vaccinated E2S1-M2e groups produced significantly higher levels of PR8 M2e-specific IgY antibodies as early as 1-week post-vaccination, while the uninoculated control and E2S1 groups remained negative for all pre-challenge time points. M2e-specific IgY antibodies capable of binding the challenge H5N3 M2e peptide were detected in groups with existing vaccine-induced M2e-specific antibodies pre-challenge, suggesting antibody M2e cross-reactivity. After challenge, all groups developed M2e-specific IgY antibodies and high HI titers, verifying successful AIV infection during challenge and production of hemagglutinin-specific antibodies. Viral shedding titers 4-days post-challenge were used to measure vaccine efficacy and were similar amongst all groups. Microneutralization assay results confirmed that post-boost serum samples, containing only M2e-specific antibodies, were unable to neutralize AIV in vitro. Although the E2S1-M2e vaccine was capable of producing high levels of M2e-specific IgY antibodies when inoculated subcutaneously, these antibodies were not able to reduce viral shedding and therefore did not protect chickens from AIV.