Question

Discuss the different ways of community reaction to agents of the disease invasion.

Answer 1

Disease refers to conditions that impairs normal tissue function.

An infectious disease is a disease that is caused by the invasion of a host by agents whose activities harm the host tissues and can be transmitted to other individuals.

Microorganisms that are capable of causing diseases are called pathogens. A true pathogen is an infectious agent that causes disease in virtually any susceptible host . Opportunistic pathogens are potentially infectious agents that are rarely cause diseases in individuals with healthy immune system.

Infection and disease are not synonymous. Infection results when a pathogen invades and begins growing within a host. Disease result only if and when as a consequence of the invasion and growth of the pathogen, tissue function is impaired.

In order to cause disease, pathogens must be able to enter the host body, adhere to specific host cells , invade and colonize host tissues and inflict damage on these tissues. Entrants through the host typically occurs through natural orifices such as the mouth eyes ,or genital openings or through wounds that breach the skin barriers to pathogens.

There are 5 major types of infectious agents. They are bacteria, virus, fungi, protozoa and helminths.

Bacteria are unicellular prokaryotic organisms . They have no internal membranous structures such as nuclei, mitochondria or lysosomes. There are variety of morphologies among bacteria, but three of the most common are bacillus, crocus or spirillum.

Bacteria are frequently divided into two broad classes based on their cell wall structures, which influences their gram stain reaction. Gram negative bacteria appears pink and gram positive bacteria appears purple after staining.

Eg: salmonella typhi, staphylococcus aureus.

Viruses are the microorganism that infects all organisms from plants to bacteria. They have no metabolism and cannot reproduce . Virus is composed of a viral genome of nucleic acid surrounded by a protein coat called capsid. Viruses are classified using a variety of criteria including shape, size and type of genome.

Eg: rhinovirus , rota virus

Fungi are eukaryotic heterotrophic organism that have rigid cellulose and chitin based cell walls and reproduce primarily by forming spores. Most fungi are multicellular ,some are unicellular. Examples of disease caused by fungi are ringworm and histoplasmosis . Yeasts of the candida genus are opportunistic infections that may cause diseases such as vaginal infection and thrush among people who are immunocompromised or undergoing antibiotic therapy.

Protozoa are unicellular heterotrophic eukaryotes that include the familiar amoeba and paramoecium. Because protozoa don't have cell walls. They are capable of a variety of rapid and flexible movements.  

Eg: giardia lamblia and cryptosporidium parvum.

Helminths are simple invertebrate animals ,some of which are infectious parasites. They are multicellular and have differentiated tissues. Because they are animals, their physiology is similar in some ways to ours. This makes parasitic helminth infections difficult to treat because drugs that kills helminths are frequently very toxic to human cells

Eg: trichinella spiralis.