The Association Between SAα2,3Gal Occurrence Frequency and Avian Influenza Viral Load in Mallards (Anas Platyrhynchos) and Blue-Winged Teals (Spatula discors)

Abstract

Background: Individual heterogeneity in pathogen load can affect disease transmission dynamics; therefore, identifying intrinsic factors responsible for variation in pathogen load is necessary for determining which individuals are prone to be most infectious. Because low pathogenic avian influenza viruses (LPAIV) preferentially bind to alpha-2,3 sialic acid receptors (SAα2,3Gal) in the intestines and bursa of Fabricius in wild ducks (Anas and Spatula spp.), we investigated juvenile mallards (Anas platyrhyncos) and blue-winged teals (Anas discors) orally inoculated with A/northern pintail/California/44221-761/2006 (H5N9) and the virus titer relationship to occurrence frequency of SAα2,3Gal in the intestines and bursa. To test the natural variation of free-ranging duck populations, birds were hatched and raised in captivity from eggs collected from nests of free-ranging birds in North Dakota, USA. Data generated from qPCR were used to quantify virus titers in cloacal swabs, ileum tissue, and bursa of Fabricius tissue, and lectin histochemistry was used to quantify the occurrence frequency of SAα2,3Gal. Linear mixed models were used to analyze infection status, species, and sex-based differences. Multiple linear regression was used to analyze the relationship between virus titer and SAα2,3Gal occurrence frequency. Results: In mallards, we found high individual variation in virus titers significantly related to high variation of SAα2,3Gal in the ileum. In contrast to mallards, individual variation in teals was minimal and significant relationships between virus titers and SAα2,3Gal were not determined. Collectively, teals had both higher virus titers and a higher occurrence frequency of SAα2,3Gal compared to mallards, which may indicate a positive association between viral load and SAα2,3Gal. Statistically significant differences were observed between infected and control birds indicating that LPAIV infection may influence the occurrence frequency of SAα2,3Gal, or vice versa, but only in specific tissues. Conclusions: The results of this study provide quantitative evidence that SAα2,3Gal abundance is related to LPAIV titers; thus, SAα2,3Gal should be considered a potential intrinsic factor influencing variation in LPAIV load.

Differential gene expression reveals host factors for viral shedding variation in mallards (Anas platyrhynchos) infected with low-pathogenic avian influenza virus

“…All LPAIV-infected birds tested positive for LPAIV, as demonstrated by at least one cloacal swab, ileum tissue or bursa tissue sample with a Ct value <40 on qRT-PCR [23,95], whereas all uninfected control birds tested negative. No individuals died prior to scheduled euthanasia or exhibited signs of disease, such as ruffled feathers, lethargy or gross pathology, consistent with previous findings [96].…”

“…Eggs were collected from hen nests located in uncultivated fields of Towner County, North Dakota, USA (48.44, -99.31) in May-June 2015, and shipped to MSU where they were incubated (Sportsman 1502 Egg Incubator; GQF Manufacturing) at 37.5 °C with 45-50 % humidity until hatched. Full details of egg collection and raising ducks can be found in Dolinski et al [23].…”

“…Previous analysis of virus titre data in mallards determined that 99 % of cumulative LPAIV was detected during the first 5 DPI [23], and birds were observed to disproportionately shed LPAIV according to the 20/80 rule [39]; therefore, birds in LPAIV-infected groups I1, I2 and I5 were subdivided into three shed level groups (Fig. 2).…”

“…Extrinsic host factors linked to heterogeneity in pathogen shedding include food availability [15,16], geographical location [17], toxicant exposure [18] and myriad environmental factors that can affect host immune competence through chronically elevated stress hormones [19]. Intrinsic factors linked to pathogen shedding are a host's age [20], sex [21,22], physiology [23][24][25] and the immune response [25][26][27]. In particular, observing how intraspecific variation in pathogen shedding relates to variation in host biological processes can improve our understanding of host factors involved in pathogen transmission.…”

“…Wild waterfowl are the natural reservoirs for low-pathogenic avian influenza virus (LPAIV), a virus transmitted via the faecal-oral route directly or indirectly through AIV-contaminated water sources [38]. Previous studies have shown that LPAIV-infected wild-bred mallards exhibit extreme heterogeneity in pathogen shedding [39], which has been linked to both extrinsic (food availability) [16] and intrinsic (gut physiology) [23] host factors. Yet, these factors alone do not explain all the observed variation in viral shedding.…”