The pathogenesis of persistent foot-and-mouth disease virus (FMDV) infection was investigated in 46 cattle that were either naive or had been vaccinated using a recombinant, adenovirus-vectored vaccine 2 weeks before challenge. The prevalence of FMDV persistence was similar in both groups (62% in vaccinated cattle, 67% in nonvaccinated cattle), despite vaccinated cattle having been protected from clinical disease. Analysis of antemortem infection dynamics demonstrated that the subclinical divergence between FMDV carriers and animals that cleared the infection had occurred by 10 days postinfection (dpi) in vaccinated cattle and by 21 dpi in nonvaccinated animals. The anatomic distribution of virus in subclinically infected, vaccinated cattle was restricted to the pharynx throughout both the early and the persistent phases of infection. In nonvaccinated cattle, systemically disseminated virus was cleared from peripheral sites by 10 dpi, while virus selectively persisted within the nasopharynx of a subset of animals. The quantities of viral RNA shed in oropharyngeal fluid during FMDV persistence were similar in vaccinated and nonvaccinated cattle. FMDV structural and nonstructural proteins were localized to follicle-associated epithelium of the dorsal soft palate and dorsal nasopharynx in persistently infected cattle. Host transcriptome analysis of tissue samples processed by laser capture microdissection indicated suppression of antiviral host factors (interferon regulatory factor 7, CXCL10 [gamma interferon-inducible protein 10], gamma interferon, and lambda interferon) in association with persistent FMDV. In contrast, during the transitional phase of infection, the level of expression of IFN-λ mRNA was higher in follicle-associated epithelium of animals that had cleared the infection. This work provides novel insights into the intricate mechanisms of FMDV persistence and contributes to further understanding of this critical aspect of FMDV pathogenesis.IMPORTANCE The existence of a prolonged, asymptomatic carrier state is a political impediment for control and potential eradication of foot-and-mouth disease (FMD). When FMD outbreaks occur, they are often extinguished by massive depopulation of livestock due to the fear that some animals may have undiagnosed subclinical infection, despite uncertainty over the biological relevance of FMD virus (FMDV) persistence. The work described here elucidates aspects of the FMDV carrier state in cattle which may facilitate identification and/or abrogation of asymptomatic FMDV infection. The divergence between animals that clear infection and those that develop persistent infection was demonstrated to occur earlier than previously established. The host antiviral response in tissues maintaining persistent FMDV was downregulated, whereas upregulation of IFN-λ mRNA was found in the epithelium of cattle that had recently cleared the infection. This suggests that the clearing of FMDV infection is associated with an enhanced mucosal antiviral response, whereas FMDV persistence...
Studies were conducted in containment facilities at Frederick, MD to determine the genetic basis of resistance to Phakopsora pachyrhizi Syd. (incitant of soybean rust) carried by the soybean [Glycine max (L.) Merr.] line PI 459025. Previous studies showed that soybean genotypes PI 200492, PI 230970, and PI 462312 each carried a single dominant gene conferring resistance to a specific soybean rust isolate. Genotype PI 200492 gave a near‐immune reaction to rust isolate India 73‐1 and a susceptible reaction to Taiwan 72‐1. Genotype PI 462312 gave a resistant reaction to the India rust isolate and a susceptible reaction to the Taiwan isolate. Genotype PI 230970 and F4 lines having PI 230970 as a parent gave resistant reactions to both rust isolates. Genotype PI 200492, PI 230970, and PI 462312 gave a susceptible reaction when inoculated with rust isolate Taiwan 80‐2. Line PI 459025 was identified as resistant to Taiwan 80‐2 as well as Taiwan 72‐1 and India 73‐1. Line PI 459025 was crossed with each of the three previously identified sources of resistance. The F1 plants, F2 populations, and selected F3 lines were inoculated with each of the three rust isolates to determine their reaction. For each plant evaluated, a leaflet of a single trifoliolate leaf was inoculated with a different rust isolate. The results showed that PI 459025 carried a single dominant gene for resistance to all three rust isolates and that this gene was at a different locus from the three previously identified genes conferring resistance to specific rust isolates. The genotype assigned for rust resistance of PI 459025 is rpp1 rpp1 rpp2 rpp2 rpp3 rpp3 Rpp4 Rpp4.
Eight soybean [Glycine max (L.) Merr.] cultivars previously identiifed as resistant to soybean mosaic virus (SMV) and three susceptible cultivars were used in a study to determine the inheritance of reaction to SMV. Field‐grown F2 and F3 populations were inoculated with virus strain SMV‐1. Greenhouse studies were also conducted in which the stock was inoculated and the reaction of homozygous and heterozygous scions determined. A variant of SMV‐1, designated SMV‐l‐B, was isolated and used to inoculate cultivars showing differential reactions to SMV‐1. Two types of resistance were recognized. The highest level of resistance gave complete protection against both SMV‐1 and SMV‐l‐B. The lesser level of resistance gave protection against SMV‐1 in the homozygous condition, but some of the heterozygous plants were necrotic. All homozygous plants became necrotic after inoculation with SMV‐l‐B. We proposed that the highest level of resistance be symbolized Rsv Rsv, the lesser level of resistance as rsvt rsvt, and the susceptible as rsv rsv. Rsv, rsvt, and rsv form an allelomorphic series with Rsv dominant to rsvt and rsv; and rsvt dominant to rsv.
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