Outcome 2.1 - Aetiology Flashcards
Name the 2 categories of pathogen + example
Opportunistic pathogen(Staphylococcus epidermis) or true pathogen(HIV)
What are true pathogens?
Microbes with well-developed character of virulence that are capable of causing disease in healthy individuals
What are opportunistic pathogens?
Microbes which normally do not cause disease in healthy individuals but can in immuno-compromised indivduals
What is virulence?
The severity of pathogenicity(disease causing properties)
Define aetiology
The study of the causation of disease, the study and identification of microbes responsible for disease
Define epidemiology
Study of the occurence, spread and control of disease in defined populations
What is Koch’s postulates used to prove
That a particular microbe is the cause of a particular disease
Name the 4 Kochs postulates
- The microbe must be present in every case of the disease
- The microbe must be isolated from the patient and grown in pure cultures
- The disease must be reproduced when the culture is introduced to a non-diseased susceptible host
- The microbe must be shown to be isolated from the experimentally infected host
What is a portal of entry?
The portal through which a microbe invades, gaining acces to the hosts tissue and sometimes cells
Name the 4 portals of entry
Skin
Respiratory Tract
Gastrointestinal Tract
Urogential Tract
Describe skin as a portal of entry
Skin be a portal of entry for a microbe that invades via infecting wounds(Staphlococcus epidermis), bites from infected insect carriers(malaria), abbrasions in skin like cold sores and genital herpes can admit viruses (Human Papillomavirus)
Describe the respiratory tract as a portal of entry
Microbes can enter the oral or nasal apertures and infect the upper respiratory tract (influenza virus or strep throat caused by bacteria) or the lower respiratory tract (pneumonia - caused by streptococcus pneumoniae bacteria or the fungi pneumocyctis)
Describe the gastronintestinal tract as a portal of entry
GI pathogens can be ingested in food or drink. Salmonella is caused by bacteria and cryptosporadium is a protazoa which causes diarehea.
Describe the urogenital tract as a portal of entry
Microbes infecting the urogenital tract can be transmitted during sexual intercourse.
Viruses - HIV and Hepatitis B
Bacteria - Syphillis, chlymadia, gonorhea
Fungus - yeast
Infection can occur directly or indirectly - explain
Hosts can be infected by direct means - contact with an infected person. Or indirect means - contact with contaminated articles or surfaces
Define infective dose
The number of organisms required to establish a productive infection. The smaller the infective does required, the more virulent the organsim
Name the 5 portals of exit
Skin Respiratory Urogenital Faecal route Blood-borne infections
Describe skin as a portal of exit
As dead skin cells are constantly shed from skin, this allows transmission of HPV, Herpes simplex virus Staphylococcal bacteria etc from boils
Describe the respiratory portal of exit
Coughing spreads droplets containing aerosols of pathogen. E.g tuberculosis, influenza and measles
Describe the faecal route as a portal of exit
Enteric (meaning intestinal) pathogens cause watery diarrhoea which provides a mechanism through which copius amounts of pathogen are released
Describe the urogenital tract as a portal of exit
Semen and vaginal secretions can contain pathogens such as HIV chlymadia.
Urine can release pathogens that infect the bladder or kidneys
Descibe blood borne infections in the context of portals of exit
Some viruses and protazoans can be transmitted by blood if it enters wounds of another person. E.g needle sharing - HIV and mosquito bites - plasmodium (malaria)
Define localised and systemic infection
Localised infection - The infection is limited to a specific tissue
Systemic infection - The infection can be spread throughout the body, typically via the bloodstream
Give an example of a localised infection and an example of a systemic infection
Localised infection - a wart or boil
Systemic infection - HIV
What is toxaemia
The result of a localised infection producint toxins which cause systemic damage after transportation in the blood e.g tetanus enters through a skin wound but toxins are carried in the blood which damage nerve cells
What are mixed infections
When two or more pathogens infect an
individual. The first or primary infection can overload or damage the host defences enough to facilitate a secondary infection.
Name the four stages of patient response to pathogenic infection
- Incubation period
- Prodromal stage
- Period of invasion
- Convalescent period
Describe the incubation period of patient response to pathogenic infection
The pathogen has not replicated sufficiently to generate symptoms, but replication continues. This period can last up to 30 days
Describe the prodromal stage of patient response to pathogenic infection
The earliest symptoms occur such as general malaise, headache, muscle pains-appear. This lasts a few days
Describe the period of invasion of patient response to pathogenic infection
The organism is in its invasive phase and toxins may be
produced to give rise to many symptoms and discomfort. The organism replicates at high levels. The host immune system will give rise to symptoms also e.g. fever, mucus production etc.
Describe the convalescent period of patient response to pathogenic infection
the immune system gradually brings the infection
under control and usually eliminates the microbe. Although the microbe can become latent, that is still capable of causing disease, but temporarily inactive- early HIV infection is an example of this phenomenon
