Characteristics features of Exotoxins and Endotoxins Reservoir of infection All infectious diseases are produced by living organisms when they invade susceptible hosts. The usual places where these organisms lives and multiply are called reservoirs of infection. These are man, animal, plant, soil or inanimate organic matter which support primarily the survival of an infectious agent. Most of the infectious diseases which occur in man are more or less specific to man and therefore must be derived from some other infected person. Man is therefore the important reservoir of most infectious diseases. The nex t imp ortant res erv oir of organi sms cap abl e of inf ect ing man is the anima l kingdom. The domestic animals and rodents are the principal animal reservoirs. Soi l is ano the r imp ort ant res ervoir of sev era l infect ive organisms. A numbe r ofpathogenic and invasive fungi are indigenous to the soil. Several pathogenic but non-invasive bacteria such as Clostridium tetani, C. botulinum, C. perfringens, etc. are commonly found in the soil. Some protozoan species grow under suitable conditions in the soil. 1. Source of infection: The term source of infection is described as the thing, person, orobject from which an infectious agent passes immediately to the host. The source ofinfection may be at any point in the chain of transmission. The source of infection may be a vehicle, eg. Contaminated water in typhoid; a biological vector eg. A mosquito in malaria; or a fomite eg. A toy in diphtheria. Most infectious agents of man and animals may be transmitted from one to another by various body fluids. The principal sources ofinfectious body fluids are spoken of as Portals of exit. 2. Portals of exit: Communicability or transmission of a disease is dependent on two important factors: (i) the escape of the infective organism from its host and (ii) the entry of the infective organism from the reservoir will depend upon the site of their growth in the body of the host, i.e. the localization of the infection in the host. (i) Respiratory tract: Respiratory pathogens such as Diplococcus pneumoniae , Corynbacterium diphtheriae , Mycobacteriumtuberculosis , Bordetella pertusis, and many viruses, and fungi, leave the infected person by the orale or nasal route in saliva and respiratory exudates. Control of diseases which spread through these channels is more difficult than that of those escaping through other channels. (ii) Intestinal/urinary tract: The enteric pathogens such as Salmonella, Shigella and Brucella spp. as well as some viruses, protozoa, and helminthes which
