<Li> fecal - oral transmission--usually from contaminated food or water sources </Li> <Li> vector borne transmission--carried by insects or other animals . </Li> <P> Yersinia pestis circulates in animal reservoirs, particularly in rodents, in the natural foci of infection found on all continents except Australia . The natural foci of plague are situated in a broad belt in the tropical and sub-tropical latitudes and the warmer parts of the temperate latitudes around the globe, between the parallels 55 degrees North and 40 degrees South . Contrary to popular belief, rats did not directly start the spread of the bubonic plague . It is mainly a disease in the fleas (Xenopsylla cheopis) that infested the rats, making the rats themselves the first victims of the plague . Infection in a human occurs when a person is bitten by a flea that has been infected by biting a rodent that itself has been infected by the bite of a flea carrying the disease . The bacteria multiply inside the flea, sticking together to form a plug that blocks its stomach and causes it to starve . The flea then bites a host and continues to feed, even though it cannot quell its hunger, and consequently the flea vomits blood tainted with the bacteria back into the bite wound . The bubonic plague bacterium then infects a new person and the flea eventually dies from starvation . Serious outbreaks of plague are usually started by other disease outbreaks in rodents, or a rise in the rodent population . </P> <P> Since human plague is rare in most parts of the world, routine vaccination is not needed other than for those at particularly high risk of exposure, nor for people living in areas with enzootic plague, meaning it occurs at regular, predictable rates in populations and specific areas, such as the western United States . It is not even indicated for most travellers to countries with known recent reported cases, particularly if their travel is limited to urban areas with modern hotels . The CDC thus only recommends vaccination for: (1) all laboratory and field personnel who are working with Y. pestis organisms resistant to antimicrobials; (2) people engaged in aerosol experiments with Y. pestis; and (3) people engaged in field operations in areas with enzootic plague where preventing exposure is not possible (such as some disaster areas). </P>

What was the vector of the bubonic plague