Vehicle Transmission

In vector transmissions, pathogens can be spread through the air and in water, food products, and body fluids (such as blood and semen). Airborne microorganisms mainly come from animals, plants, water, and soil. These microorgan isms can transmit disease through air. They can travel one meter or more through an air medium to spread infection.

Airborne pathogens have the greatest chance of infecting new individuals when these individuals are crowded together indoors or in a climate-controlled building where heating and air conditioning units regulate temperature and very little fresh air enters the building. Airborne pathogens can fall to the floor and combine with dust particles. This dust can then be stirred up with walking, dry mopping, or changing bedding and clothing. Examples of diseases that are transmitted by airborne transmissions and dust particles are measles, chickenpox, histoplasmosis, and tuberculosis.

Waterborne microorganisms that cause pathologies do not grow in pure water. They can survive in water with small amounts of nutrients but thrive in polluted water, such as water contaminated with fertilizer and sewage (which is rich in nutrients). Waterborne pathogens are usually transmitted in contaminated water supplies by either untreated or inadequately treated sewage. Indirect fecal-oral transmission of pathogens occurs when the disease-causing microorganism living in the fecal matter of one organism infects another organism. Bacterial pathogens infect the digestive system, causing gastrointestinal signs and symptoms. Examples of waterborne diseases are shigellosis and cholera.

Foodborne pathogens are normally transmitted through improperly cooked or improperly refrigerated food, or unsanitary conditions. Improper hygiene of the part of food handlers also plays a key role in foodborne transmission. Food-borne pathogens can produce gastrointestinal signs and symptoms. Examples of foodborne diseases are salmonellosis, typhoid fever, tapeworm, and listeriosos.

Vector Transmission

Vector spread is the transmission of an infectious agent by a living organism to humans. Most vectors are ticks, flies, and mosquitoes. These organisms are called arthropods. Vectors can transmit disease in two ways. First, mechanical vectors can passively transmit disease with their bodies. An example is the common housefly.

These animals commonly feed on fecal matter. They then fly to feed on human food, transmitting pathogens along the way. Keeping mechanical vectors away from food preparation and eating areas are means of prevention. Remember: The fly that is walking across your picnic lunch may have just walked across dog or cat feces. Examples of a few diseases transmitted by mechanical vectors are diarrhea caused by E. coli bacteria, conjunctivitis, and salmonellosis.

The second type of vectors are biological vectors and can actively transmit disease-causing pathogens that complete part of their life cycle within the vector. In most vector-transmitted diseases, a biological vector is the host for a phase of the life cycle of the pathogen. An example of a host organism is a mosquito that infects a human with malaria. Other diseases caused by biological transmission vectors are yellow fever, the plague, typhus, and Rocky Mountain spotted fever.

To cause infection, a microorganism must enter the body and have access to body tissues. The sites where microorganisms enter the body are called portals of entry. The portal of entry is similar to the portal of exit for the host to be susceptible for a certain disease. The portals of entry include the skin, digestive tract, respiratory tract, and urinary tract. Microorganisms can invade tissues directly or cross the placenta to infect the fetus. Skin that is intact prevents most microorganisms from entering the body, although some enter the ducts of sudoriferous glands (sweat glands) and hair follicles to gain entrance into the body.

Fungi can invade cells on the surface of the body and some can even invade other tissues. The larvae of parasitic worms can work their way through the skin and enter tissues. An example of a parasitic worm is the hookworm.

Mucous membranes make direct contact with the external environment. This allows microorganisms to enter the body. Examples of mucous membranes are the eyes, nose, mouth, urethra, vagina, and anus. The respiratory tract is an area of the body where microorganisms typically enter on dust particles that are inhaled with air or in aerosol droplets. Microorganisms that infect the digestive tract, are normally ingested with contaminated water or food, or even from biting the nails of contaminated fingers.

Many genitourinary infections are the result of sexual contact. Skin that is not intact due to injury, surgery, injections, burns, and bites makes it easy for invading microorganisms to penetrate body tissues. Common portals of entry are insect bites. Many parasitic diseases are caused by the bites of insects. Some diseases can affect the fetus through the placenta of an infected mother. Viruses such as the HIV virus, rubella (German measles), and the bacteria that cause syphilis behave in this way.

The transmission of disease by carriers causes epidemiological problems because carriers usually do not know they are infected and spread the disease, causing sudden outbreaks. Carriers can transmit disease by direct and indirect contact or through vehicles, such as water, air, and food.

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