Final answer:
The correct answer is option d . The pathogen most likely responsible for a chicken farmer's encephalitis after pneumonia is Cryptococcus neoformans, a yeast that can cause meningitis, particularly in individuals with compromised immune systems.
Step-by-step explanation:
If a chicken farmer is diagnosed with encephalitis following symptoms of pneumonia, the pathogen most likely responsible is Cryptococcus neoformans. This pathogen is a type of encapsulated yeast that can infect the central nervous system (CNS), causing meningitis. It is particularly associated with bird droppings, which is likely to be found in a farm environment. Cryptococcus neoformans infection can be severe for individuals with compromised immune systems. Considering that the other options, such as Trypanosoma brucei rhodesiense (cause of African trypanosomiasis), Mycobacterium leprae (cause of Hansen's disease or leprosy), and Listeria monocytogenes (a bacterium that can cause listeriosis), are not commonly associated with bird droppings or present with pneumonia followed by encephalitis, Cryptococcus neoformans stands out as the most likely culprit. Therefore, the correct option in the final answer is d. Cryptococcus neoformans.