A poultry farmer keeps 500 layers in a free-range system. Over a two-week period the farmer records the number of birds showing respiratory symptoms each da...

Labelled answer diagram:

(a)(i) The structures labelled in the diagram of the chicken respiratory system:

• P = Trachea (windpipe) - the main airway connecting the larynx to the bronchi [1].
• Q = Bronchus (primary bronchus) - the branch that carries air from the trachea into the lung [1].
• R = Air sac - the thin-walled extension of the respiratory system unique to birds, which stores air and facilitates unidirectional airflow through the lungs [1].

(a)(ii) How Newcastle disease affects the respiratory system (3 marks):

1. The Newcastle disease virus (a paramyxovirus) attacks and inflames the epithelial lining of the trachea and bronchi, causing swelling and excess mucus production [1].
2. Affected birds show gasping, coughing, sneezing and nasal discharge as they struggle to move air through the inflamed, mucus-clogged airways [1].
3. The air sacs may become clouded or thickened, reducing gas exchange efficiency. In severe cases the respiratory damage allows secondary bacterial infections to establish, worsening the condition [1].

(b) How Newcastle disease spreads between birds (3 marks):

1. Direct contact - healthy birds become infected through close contact with sick birds or their respiratory secretions [1].
2. Airborne droplets - coughing and sneezing release virus-laden aerosol droplets that nearby birds inhale [1].
3. Fomites and environment - contaminated feed, water, equipment, litter and droppings carry the virus. Wild birds, rodents and human visitors can also transport the virus between farms on their bodies or clothing [1].

(c)(i) A suitable vaccination programme for Newcastle disease (3 marks):

1. Vaccinate chicks at day-old with a live attenuated vaccine (e.g. Hitchner B1 strain) administered by eye drop or in the drinking water [1].
2. Give a booster vaccination at 3-4 weeks of age to strengthen immunity as maternal antibodies wane [1].
3. Revaccinate layers every 8-12 weeks (or as recommended by the vaccine manufacturer) to maintain protective antibody levels throughout the laying period. Keep written records of vaccination dates and batch numbers [1].

(c)(ii) Three biosecurity measures apart from vaccination (any three for [3]):

1. Restrict access - limit entry to the poultry house to essential workers only and provide disinfectant footbaths at every entrance, so that pathogens are not carried in on shoes or clothing [1].
2. All-in, all-out management - do not mix birds from different sources or age groups. Bringing in birds of uniform age and origin, then cleaning thoroughly between batches, prevents disease cycling between cohorts [1].
3. Prompt carcass disposal - remove and bury or burn dead birds immediately rather than leaving them on the farm, eliminating a major source of virus amplification and environmental contamination [1].

Also acceptable: netting open sides to exclude wild birds; cleaning and disinfecting feeders, drinkers and equipment regularly.