This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Haemophilus, Yersinia, Spirochaetes, Ricketssia, Chlamydia, Mycoplasma and Miscellaneous Bacteria), Subject name: Microbiology
Which of the following statements is true about endemic typhus: 
Select and explain. 
A. ls caused by R. rickettsii, B. ls transmitted by bites of fleas, C. Has no Mammalian reservoir, D. Can be cultured in chemical defined culture medium
B: ls transmitted by bites of fleas
Answer: B: ls transmitted by bites of fleas 
Explanation: Option 1, 2, 3 Endemic typhus: Causative agent- R. typhi Vector - Flea, Rats are the reservoir Option 4 Rickettsiae cannot be cultivated in cell free media. Isolation can be done by cell lines (Vero, primary chick embryo, WI-38, HeLa), egg (yolk sac inoculation), or animal inoculation (guinea pig).