Routes of spread of infection:
There are five main routes by which a host may become infected.
1. The respiratory route
2. The alimentary tract
3. Genital tract
4. The skin and mucous membrane
Organisms causing respiratory infections are as follows. Streptococcus pneumoniae, Haemophilus influenzae, Mycobacterium tuberculosis, Bordetella pertusis are some of the bacterial pathogens. Common cold virus, influenza virus, adno virus are some of the viruses producing respiratory infections.
The intestinal diseases like cholera, bacillary dysentery, the enteric fever and bovine tuberculosis are contracted when the organisms are ingested. But in the case of entero virus infections (poliomyelitis) and Hepatitis though the organisms enter through gastro intestinal system, the effects are seen elsewhere in the body.
Organisms may be acquired from the skin as in the case of herpes virus infection or through wounds as in tetanus. Wounds may be formed from trauma or thorn pricks or needle stick injury. Organ-isms may also be introduced through animal bite as in the case of rabies or by insect bites as in dengue, malaria, filariasis, and yellow fever.
Syphilis , gonorrhea, hepatitis B and AIDS are some of the sexu-ally transmitted diseases. Treponema pallidum, Neisseria gonorrhoeae, Hepatitis B virus and Human Immunodeficiency Virus are the etiologic agents respectively.
Bacteria like T.pallidum, Viruses like rubella, cytomegalovirus, parasite like Toxoplasma gondii are some of the organisms that enter through placenta and cause disease in the newborn.