Page 165 - Concise Pathology for Exam Preparation ( PDFDrive )

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Infections

General terminology pertaining to infectious diseases
• Infectious diseases are transmissible or communicable diseases that can spread
directly (person to person) or indirectly (through a mediator, eg, air, water, food, living
vector or an object-vehicle).
• They are caused by pathogenic micro- or macro-organisms, such as bacteria, viruses,
parasites or fungi and have characteristic ‘symptoms and signs’ resulting from the in-
troduction of the pathogenic biological agent into the host body and its subsequent
multiplication. In some cases, infectious diseases may not be clinically evident (are
asymptomatic) for most or their entire course.
• The term ‘infection’ may not necessarily indicate ‘disease’, as some infections lie dormant
in the host without causing visible illness.
• The term infectivity indicates the ability of an organism to gain entry into and prolifer-
ate in the host, while infectiousness of a disease indicates the rate at with which it is
transmitted to other hosts.
• A contagious disease is a type of infectious disease that is easily transmitted by contact.
Infectious diseases with more specialized routes of infection, such as vector or sexual
transmission, are usually not regarded as ‘contagious’, and often do not require medical
isolation (quarantine) of victims.
• Virulence is defined as the likelihood of an organism causing severe or aggressive disease
(degree of pathogenicity).
• Primary pathogens are those which cause disease in a normal, healthy host, due to
their inherent virulence.
• Organisms that cause disease in an immunosuppressed host are termed as opportunis-
tic pathogens. These may be a part of normal host flora (Candida) or may be acquired
from the environment (eg, introduction via surgical or traumatic wound infections).
• Zoonotic diseases are infectious diseases of animals that can be transmitted to humans
through animal contact, bite, secretions or vectors.
• Epidemiology is a tool used to study disease in a population. It is important to deter-
mine whether an infectious disease outbreak is sporadic (has an occasional occurrence),
endemic (occurs regularly at a certain frequency in a region), epidemic (occurs at an
unusually or unexpectedly high frequency in a particular region) or pandemic (occurs
worldwide or globally as an epidemic).
• Based on the type of causative agent, infections are classified into those caused by
bacteria, viruses, fungi, protozoa, chlamydiae, rickettsia, mycoplasma and
helminths.

Q. Write in detail on various types of bacterial infections.

Ans. Common bacterial infections include

Staphylococcal Infections
• Rosenbach in 1884 described two pigmented colony types of staphylococci and called
them: Staphylococcus aureus (yellow) and Staphylococcus albus (white). The latter later
came to be known as Staphylococcus epidermidis.
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