Pathogenic Organisms Definition
Any microorganism capable of injuring its host, e.g., by competing with it for metabolic resources, destroying its cells or tissues, or secreting toxins. The injurious microorganisms include viruses, bacteria, mycobacteria, fungi, protozoa, and some helminths. Pathogenic microorganisms may be carried from one host to another as follows: Animal sources: Some organisms are pathogenic for animals as well as humans and may be communicated to humans through direct or indirect contact. Airborne: Pathogenic microorganisms such as rhinoviruses, mycobacteria, or varicella may be discharged into the air, from which infectious droplets may be inhaled by exposed persons. Bloodborne: Infections such as cytomegalovirus, hepatitis B or C, HIV/AIDS, malaria, or West Nile virus may be spread from person-to-person by injection drug use, organ transplantation, or transfusion. Contact infections: Direct transmission of microorganisms can occur by skin-to-skin or intimate body contact, as in many sexually transmitted diseases. Foodborne: Food and water may contain pathogenic organisms acquired from the handling of the food by infected persons or through fecal or insect contamination. Fomites: Inanimate objects such as linens, books, cooking utensils, or clothing that can harbor microorganisms and could serve to transport them from one location to another. Human carriers: Asymptomatic individuals (e.g., “typhoid Mary”) may harbor microorganisms without injury but transmit disease to others. Arthropod vectors: Insects, ticks, fleas, mosquitoes, and mites may transmit diseases by biting their hosts and depositing microorganisms into the blood. Soilborne: Spore-forming organisms (e.g., tetanus) in the soil may enter the body through a cut or wound. Vegetables and fruits, esp. root crops, may transmit microorganisms to the gastrointestinal tract.