Introduction to Infectious Diseases


Scanning electron micrograph of HIV-1 budding (in green) from cultured lymphocyte. Multiple round bumps on the cell surface represent sites of assembly and budding of virions. Image courtesy of CDC/ C. Goldsmith

Most people are only too well acquainted with the queasy feeling of coming down with an illness: it could simply be nausea which develops along with a headache, or perhaps a runny nose accompanied by an almost ubiquitous itch in your throat which, in turn, constantly urges you to cough. In some cases, however, the illness might be very much more severe, and cause, amongst other hugely unpleasant experiences, extreme pain, internal bleeding, the loss of consciousness and even death.

Most people have used an external hard drive to copy data only to find that hiding somewhere within the zeros and ones was a virus that unleashed havoc on their own PCs. The analogy between a digital “illness” and a biological one is apt, and, in many ways the treatment for both is also similar. The consequences of a biological infectious disease, however, can be infinitely worse than a malicious programme written by a bored social outcast intent on damaging android cell phones.

In our attempt to alleviate the discomfort of becoming sick through prevention (prevention being the best cure, after all), medical and life sciences researchers have come to understand a great deal about the human body, its constituents , their respective processes and functions, and their various interactions with one another. In addition to this, researches have done much to illuminate the mechanisms by which diseases cause the host entity to become sick (sick here meaning the cessation of normal efficient functioning caused by the presence of malicious microorganisms).

This site is designed to offer a very brief introduction to infectious diseases and their context in South Africa. This is obviously an enormously wide topic and this website strongly urges anyone who suspects that they may be ill (or contracted a communicable disease) to seek professional medical advice as soon as is possible.

Infectious diseases are also called transmissible diseases (quite uncommon in South Africa) and communicable diseases. The latter term is quite descriptive with regards to the fact that infectious diseases are not exclusive to their current host but can spread through various means (including direct contact with the host, sexual transmission, contact with contaminated foodstuffs, etc.), and the most difficult types of infectious disease to contain are those that can be transmitted via air (these are often referred to as being contagious diseases).

A good working definition of a communicable disease is that it is an illness (i.e. the patient displays various medical symptoms associated with abnormal physiological functioning) resulting from the presence and proliferation of pathogenic biological agents in a host entity or organism. Abnormal physiological functioning can either result directly from the activity of the pathogen (germ) on an organ or bodily process, or from the effects that the pathogen has with regards to secondary illnesses. In the latter case the disease is asymptomatic (without observable symptoms), but a secondary illness results directly from the first illness.

Infectious pathogens (germs) can take a variety of forms and most commonly include: bacteria, viruses, fungi, protozoa, fungi, multicellular parasites, and proteins known as prions. Pathogens disrupt normal bodily processes (as already stated) and are therefore seen as the entities that give rise to diseases and, in the worst of circumstances, epidemics and pandemics. One of Africa’s most detrimental (in terms of human suffering caused) pathogen at this point in time could well be the Human Immunodeficiency Virus and its associated condition, the Acquired Immunodeficiency Syndrome.

“Infectivity” is used to describe the ability of a pathogen to enter into a host, survive in that host, and proliferate (multiply) during its lifecycle. “Infectiousness”, in contrast, is a term used to indicate the ease with which a particular disease can be transmitted to another, previously uninfected host. Diseases with a high level of infectiousness are called contagious as they are easily transmitted by contact with an already ill person (influenza, for example, is contagious as it spreads itself from host to host with ease and rapidity). Dangerous and contagious diseases often result in an attempt to quarantine the respective pathogens via physically isolation of hosts (or victims).

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