This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
P. Carni causes infection of primarily ? 
Select and explain. 
A. Rats, B. Mice, C. Humans, D. Rabbits
A: Rats
Answer: A: Rats 
Explanation: Ans. is 'a' i.e., Rats . Although the organisms within the pneumocystis genus are morphologically very similar, they are genetically diverse and host specific --> P jirovecii infects humans, where as Pcarinii infects rats.