Megan Schilling

Newcastle Disease Virus (NDV) is an important poultry pathogen worldwide that causes significant impacts on backyard poultry in developing countries, like Tanzania, due to high morbidity and mortality.  The symptoms of NDV range from respiratory problems, like coughing and wheezing, nervous system changes, such as twitching and paralysis, or reproductive changes, including loss in egg production. Introduction of this disease into a flock could cause detrimental consequences for smallholder farmers who depend on the productivity of their flocks as a source of food and income for their family.

In Tanzania 93% of all poultry is reared in backyard or scavenging environments with poor quality feeds, little to no veterinary care, and exposure to predators and pathogens, like NDV.  It is interesting, however, that some backyard chickens have high antibody titers for NDV without exhibiting any clinical signs of the disease. These chickens are generally considered less susceptible to pathogens, including NDV, due to their pre-sensitization with higher frequencies of natural exposure to pathogens, as well as through natural selection for hardiness to higher levels of pathogen exposure.

But what contributes to this natural disease resistance in the backyard poultry? I hypothesize that innate immune mechanisms, particularly innate immune gene expression, are predictive of NDV susceptibility among different chicken ecotypes.

Traditionally, studying the immune response of chickens is through long and expensive challenge experiments or field studies with multiple confounding factors, such as environmental conditions, co-infections, variability in dosing, and nutritional status, making the results of these experiments difficult to interpret. In contrast, the chick embryo may provide a considerably cheaper option while reducing the effects of confounding variables with the shell as a protective environment to examine the early innate immune response to pathogen.

The chick embryo immune system begins to develop around the tenth day of incubation and continually develops in the following days prior to hatch at 21 days. Around the 18th day of incubation, the chick embryo becomes immunocompetent and is capable of producing both an innate and adaptive response to pathogen.  This early embryonic immune development has been exploited with in ovo vaccination for some poultry pathogens. Although in ovo vaccination has become common for some pathogens, the mechanisms of induction of protection and the immune response in chick embryos remains poorly understood.

My project aims to focus on two major aims: The first aim focuses on characterizing the innate immune response of the chick embryo in different breeds of chickens to NDV infection. This will help to characterize the innate immune mechanisms involved in the response to NDV infection. During this experiment, I will infect eggs with NDV and determine the innate immune gene expression post-infection using Real-Time Polymerase Chain Reaction (RT-PCR) or RNA sequencing. This will determine sets of genes that are differentially expressed between NDV infected and non-infected control chick embryos. The second aim focuses on determining the susceptibility of hatched chicks from different lines to NDV infection. This will be performed through experimentally infecting chicks with NDV and tracking infection phenotypes, such as viral shedding, to determine the level of susceptibility of each line to NDV infection.

The above aims will focus on inbred lines whose genetic backgrounds are extensively characterized. Through combining these two aims, we hope to determine a panel of genes that could be assessed in the chick embryo to predict the level of susceptibility of a certain breed or ecotype to NDV infection. For example here, if gene A is upregulated and genes B and C are downregulated then the chick is more susceptible to NDV infection.

Once this panel of genes is determined, we could then use it to select for resistant lines in the highly outbred ecotypes of Tanzania, which will help to inform breeding strategies. And if combined with production traits, could increase both productivity and disease resistance in backyard poultry for smallholder farmers to improve their livelihoods and have beneficial impacts on Sub-Saharan African communities and anywhere backyard poultry are farmed.