Disease-causing salmonellae have recently been re-classified into a single species, Salmonella enterica, which has numerous strains or serovars. Salmonella typhi is a well know serovar that causes typhoid fever. Other salmonellae are frequent causes of food poisoning, and can especially be caught from poultry. In the mid to late 20th century, Salmonella enterica serovar Enteritidis was a common contaminant of eggs. This is much less common now with the advent of hygiene measures in egg production and the vaccination of laying hens to prevent samonella colonisation. Many different salmonella serovars also cause severe diseases in animals other than human beings.