Determining the intrinsic factors responsible for variation in avian influenza pathogen load in wild ducks

It is increasingly apparent that some individuals in a population are more likely to contribute to transmission of disease-causing agents than others; these individuals are called ‘superspreaders’. One factor that can... [ view full abstract ]

It is increasingly apparent that some individuals in a population are more likely to contribute to transmission of disease-causing agents than others; these individuals are called ‘superspreaders’. One factor that can affect an individual’s capacity to contribute to transmission events is their infectiousness. Individuals that have higher pathogen loads than other individuals (i.e. ‘supershedders’) have the potential to lead to more secondary infections. We aim to determine the genetic and physiological basis for this variation in pathogen load using Mallards (Anas platyrhynchos) and low pathogenic avian influenza virus (LPAIV). Mallard eggs (n = 70) were collected from North Dakota in June 2015 and hatched and reared in captivity until the ducks were 6 weeks old. Birds (n = 60) were infected with LPAIV H5N9 or sham-inoculated (n = 10). Cloacal swabs and blood samples were collected from live birds for viral and antibody titers. In groups of 10 – 15 individuals, birds were sacrificed on 1, 2, 5, 15, and 29 days post infection. Intestinal tissues, spleen, and bursa were fixed in 10% buffered formalin for histological examination. Histochemical assays were used to identify and quantify host cellular features that correspond with the variation in LPAIV replication, including sialic acid receptors and mucin. Consistent with previous studies, preliminary viral titer results using RT-PCR show variation in pathogen load with a few individuals having disproportionately higher viral titers relative to remaining birds. Histochemical staining of intestinal tissues lends insight into the intrinsic basis for this observed variation in pathogen load. Understanding the mechanisms underlying high pathogen shedding has important implications for developing targeted prevention and control strategies for disease outbreaks.