(c) : Plague is an acute epidemic disease of rats and other wild rodents caused by the bacterium Yersinia pestis, which is transmitted to humans by rat fleas. Headache, fever, weakness, aching limbs, and delirium develop and are followed by acute painful swellings of the lymph nodes. Bleeding under the skin, producing black patches, can lead to ulcers, which may prove fatal. Treatment with tetracycline, streptomycin, and chloramphenicol is effective. Trichinosis is caused by Trichinella spiralis which lives as an endoparasite in human intestine. Salmonella typhimurium causes enteric fevers Leishmania donovani causes kala-azar.