Answer: Respiratory
Step-by-step explanation:
The mode of transmission of the disease is through respiratory system because it spread due to the presence of the microbes in air.
As the wind blew from northwest to other side, the pathogens were carried from one place to another along with the blowing wind.
The pathogens entered into the body by the nasal passage when the sheep inhaled the air. The pathogens entered into the body of the sheep and cause pneumonia into them. which resulted in chills, sweat, fever, fatigue et cetera.
Hence, the portal for the entry of the pathogens is the respiratory track of the sheep.