[show abstract][hide abstract] ABSTRACT: Vaccination is an attractive tool for the prevention of outbreaks of highly pathogenic avian influenza in domestic birds. It is known, however, that under certain circumstances vaccination may fail to prevent infection, and that the detection of infection in vaccinated birds can be problematic. Here, we investigate the characteristics of three serological tests (immunofluorescent antibody test (iIFAT), neuraminidase inhibition (NI) assay, and NS1 ELISA) that are able to differentiate infected from vaccinated animals. To this end, data of H7N7 infection experiments are analyzed using Bayesian methods of inference. These Bayesian methods enable validation of the tests in the absence of a gold standard, and allow one to take into account that infected birds do not always develop antibodies after infection. The results show that the N7 iIFAT and the NI assay have sensitivities for detecting antibodies of 0.95 (95% CI: 0.89-0.98) and 0.93 (95% CI: 0.78-0.99), but substantially lower sensitivities for detecting infection: 0.64 (95% CI: 0.52-0.75) and 0.63 (95% CI: 0.49-0.75). The NS1 ELISA has a low sensitivity for both detecting antibodies 0.55 (95% CI: 0.34-0.74) and infection 0.42 (95% CI: 0.28-0.56). The estimated specificities of the N7 iIFAT and the NI assay are 0.92 (95% CI: 0.87-0.95) and 0.91 (95% CI: 0.85-0.95), and 0.82 (95% CI: 0.74-0.87) for the NS1 ELISA. Additionally, our analyses suggest a strong association between the duration of virus excretion of infected birds and the probability to develop antibodies.
[show abstract][hide abstract] ABSTRACT: Domestic ducks play an important role in the epidemiology of H5N1 avian influenza. Although it is known that vaccines that have a high homology with the challenge virus are able to prevent infection in ducks, little is yet known about the ability of genetically more distant vaccines in preventing infection, disease, and transmission. Here we study the effect of a widely used H5N2 vaccine (A/Chicken/Mexico/232/94/CPA) on the transmission of H5N1 virus (A/Chicken/China/1204/04) in ducks. The quantitative analyses show that despite the low level of homology between the virus and vaccine strain transmission was significantly reduced two weeks after a single or double vaccination. Mortality and disease rates were reduced markedly already one week after a single vaccination.
[show abstract][hide abstract] ABSTRACT: Highly pathogenic avian influenza viruses can affect many bird species, with disease symptoms ranging from severe morbidity and high mortality to mild transient illness. Much is known about infections in chickens, but for other captive birds the relations between disease symptoms, excretion patterns, and transmission, as well as the effect of vaccination on these relations are not clear. We report results from experimental transmission studies with a highly pathogenic H7N7 virus and two commonly kept bird species (ringed teals and golden pheasants). The results show that depending on the host species the virus can spread in unvaccinated birds with or without disease symptoms. Vaccination reduces disease symptoms markedly, but need not always reduce virus transmission. We discuss the implications for the control of highly pathogenic avian influenza.
[show abstract][hide abstract] ABSTRACT: The effect of the neuraminidase inhibitors zanamivir and oseltamivir on the transmission of highly pathogenic avian influenza (HPAI) in chickens was studied. Per group, five chickens inoculated with HPAI A/Chicken/Pennsylvania/1370/83 H5N2 virus were placed 1 day post-inoculation (p.i.) in one cage with five contact chickens. Inoculated and contact chickens were treated twice daily from 1 day before inoculation up to day 7 p.i. All untreated inoculated and contact chickens became infected and four inoculated and two contact chickens died. Similarly, all of the zanamivir-treated inoculated and contact chickens became infected and all inoculated and four contact chickens died. Obviously, locally active zanamivir has no effect. In contrast, although oseltamivir could not prevent tracheal infection of the inoculated chickens, none had an infected cloaca and only one died. More important, only after stopping treatment three contact chickens became positive, suggesting limited transmission within or after the treatment period. In conclusion, treatment with systemically active oseltamivir limits to a large extent a severe outcome and chicken-to-chicken transmission of HPAI virus.
International Congress Series 01/2004; 1263:495-498.