What is infectious disease?
An infectious disease is a disease that damages or injures the host that results from the presence of one or more pathogenic microbial agents
including viruses, bacteria, fungi, protozoa, multi cellular parasites, and aberrant proteins known as prions
also there is a contagious disease is an infectious disease that is capable of being transmitted from one person or species to another.

What are kinds of pathogens?
Classified as either Primary pathogens or as Opportunistic pathogens according to the status of host defenses
Primary pathogens cause disease as a result of their presence or activity within the normal, healthy host, and their intrinsic virulence
Opportunistic pathogens Organisms which cause an infectious disease in a host with depressed resistance
Opportunistic disease may be caused by microbes that are ordinarily in contact with the host, such as bacteria or fungi in the gastrointestinal or the upper respiratory tract

How does transmission of infectious disease occur?

Respiratory diseases

And Meningitis are commonly acquired by contact with aerosolized droplets, spread by sneezing, coughing & talking

Gastrointestinal diseases

Are often acquired by ingesting contaminated food and water

Sexually transmitted diseases

Are acquired through contact with bodily fluids, generally as a result of sexual activity

Some infectious agents

Some infectious agents may be spread as a result of contact with a contaminated, inanimate object, such as a coin passed from one person to another, while other diseases penetrate the skin directly


Transmission of infectious diseases may also involve a "vector".

What does vector mean?
Vectors may be mechanical or biological.

Biological Vectors

Harbor pathogens within their bodies and deliver pathogens to new hosts in an active manner, usually a bite are often responsible for serious blood-borne diseases, such as malaria, viral encephalitis, such as mosquitoes, ticks, fleas and lice.

Mechanical vector

Picks up infectious agent on the outside of its body and transmits it in a passive manner. E.g. Housefly

Print this page