Many bacteria are parasitic, though since the result is infection and disease , sometimes leading to death, they are generally thought of as pathogens instead.  Parasitic bacteria are extremely diverse, and infect their hosts by a variety of routes. To give a few examples, Bacillus anthracis , the cause of anthrax , is spread by contact with infected domestic animals ; the bacillus's spores , which can survive for years outside the body, can enter a host through an abrasion or may be inhaled. Borrelia , the cause of Lyme disease and relapsing fever , is transmitted by a vector, ticks of the genus Ixodes , from the diseases' reservoirs in animals such as deer . Campylobacter jejuni , a cause of severe enteritis (gut inflammation), is spread by the fecal-oral route from animals, or by eating insufficiently cooked poultry , or by contaminated water. Haemophilus influenzae , an agent of bacterial meningitis and respiratory tract infections such as influenza and bronchitis , is transmitted by droplet contact. Treponema pallidum , the cause of syphilis , is spread by sexual intercourse .