Chain Of Transmission PDF

Chain of infection and chain of transmission BY Dr :Mariam Mohamed Alfatih YOSUF Algam MASTER DEGREE OF FAMILY MEDICINE  CHAIN OF TRANSMISSION Definition The chain of transmission is the chain...

Chain of infection and chain of transmission BY Dr :Mariam Mohamed Alfatih YOSUF Algam MASTER DEGREE OF FAMILY MEDICINE  CHAIN OF TRANSMISSION Definition The chain of transmission is the chain or cycle through which a causative agent passes from reservoir to host.  Reservoir It is the habitat, or normal environment, where the infective agent is present and where it can live, grow and multiply. This reservoir may be man, animal or environment. One of the most important characteristics of the reservoir is that it carries the last stage of the (infective) agent where a new cycle starts or it carries the stage which passes to the intermediate host. (A) Man Infection is transmitted from man in the acute clinical state or from a carrier of infection. Healthy carrier: a carrier who is not infected, e.g. niesseria meningitides in the buccal cavity. Subclinical carrier: Although he is infected but no symptoms appear. Incubatory carrier: transmit disease during incubation period where the infective agent grow and multiply. Still no symptoms like infective hepatitis. Convalescent carrier: after cure of the patient, he may carry the microbe for a variable period, like salmonella & shigella. Chronic carrier: has chronic disease where infection is transmitted for a long time, (may be more than a year) like hepatitis-B virus. Recurrent or intermittent carrier: has recurrent infection due to nature of the disease which is intermittent (on and off), like T.B. Clinical carrier: he is ill with apparent clinical symptoms. (B) Animals Animals , like vertebrates are reservoirs for many diseases (zoonotic diseases) e.g. brucellosis, anthrax, haemorrhagic fevers, and others act as vectors as for relapsing fever, malaria and lieshmaniasis. (C) Environment some microbes grow and multiply in the environment then get transmitted to man in food or water or soil. Agent Agent factors depend on dose, pathogenicity and virulence and include known biological agents (Refer to agent factors in epidemiological triangle of the determinants) e.g. protozoa, metazoa, bacteria, viruse s, fungi…etc. Exit 1-Respiratory tract: through cough, sneezing and sputum, like influenza and tuberculosis. 2-Genitourinary tract: sexually transmitted infections STI like gonorrhoea, syphilis and AIDS. 3-Gastro-intestinal tract: through saliva like rabies, or through feces, e.g. infective hepatitis and typhoid. 4-Skin: like skin fugal infections and hepatitis B. 5-In utero: from mother to infant through umbilical cord like syphilis and AIDS. Mode of transmission Transmission is either direct or indirect. Direct transmission: reservoir is very near or close to the host : a) From one person to another through direct contact like STI. b) Droplet infection: like cough, sneezing and sputum where the distance is near (3 to 6 feet). Indirect transmission: (reservoir and host are far from each other by a distance of feet to miles) A-Vector spread through vectors like mosquitos, lice, bugs or through legs and wings e.g. flies. B-Vehicle spread through non-living bodies called fornites like dolls, cups and spoons or through organic materials like canned or frozen foods or milks. C-Air – borne spread through minute particles (1-5 microns), micro-drops which move freely in air current and stay for variable periods according to physical and climatic conditions.  Agent The chain is completed by agent and host. Agent factors depend on dose, pathogenicity and virulence and include known biological agents (Refer to agent factors in epidemiological triangle of the determinants) e.g. protozoa, metazoa, bacteria, viruses, fungi…etc. Entry Entry is similar to exit as transmission occurs from respiratory tract to respiratory tract, from feces to mouth (foeco-oral), from skin to skin, from uterus to foetus and from genital to genital organs. Host Host is the last ring of the chain of transmission and can be a reservoir to transmit disease to another person where a new cycle starts. Host factors related to infection include susceptibility, immunity and resistance. General resistance factors - Healthy skin. - Cough reflex. - Gastric juice. - Diarrhea. - Normal flora. Specific immunity factors - WBCs. - Serological factors and lymphocytes - immunity if either active or passive, natural or acquired. - immunity system including t-lympoeytes and anti- bodies. THANKS GOD