MIC1PE exam

Infection

A microbe growing or multiplying on or within a host.

Infectious disease

Any change in health where part or all of the host is incapable of functioning normally.

Disease

A broad term that encompasses any abnormal condition that affects the normal functioning of a living organism, including humans, caused by factors such as genetics, lifestyle choices, or environmental factors.

Pathogen

Any organism that causes disease.

Opportunistic pathogen

A pathogen that doesn't typically cause harm to a healthy individual with an intact immune system but can cause infections if the immune system is compromised or weakened.

Pathogenicity

The ability for a microorganism to cause disease in a susceptible host.

Virulence

A quantitative measure of the degree or severity of the pathogenicity of a microorganism, representing the extent of harm inflicted upon the host.

Incubation period

The period after pathogen entry but before the appearance of signs and symptoms.

Prodromal stage

The onset of signs and symptoms that are not clear enough for a diagnosis.

Illness period

The most severe point of disease regarding signs and symptoms, which sometimes culminates in death.

Convalescence

The stage where signs and symptoms of an infectious disease begin to disappear.

Signs

Objective changes in the body experienced by the patient.

Symptoms

Subjective changes experienced by the patient, such as pain or loss of appetite.

Transmission

The process by which an infection or disease travels from one host to another.

Epidemiology

The science that evaluates occurrence, determinants, distribution, and control of health and disease in a defined human population.

Sporadic disease

A disease that occurs occasionally or at irregular intervals, occurring one at a time and in areas separated geographically.

Endemic disease

A disease maintained at a relatively steady low-level frequency at a moderately regular interval, constantly present in a population or area.

Outbreak

A sudden, unexpected occurrence of a disease in a limited segment of the population.

Epidemic

A sudden increase in the level of disease above what is normally expected in a given population or area, typically within a smaller and more limited geographic area than an outbreak.

Pandemic

An epidemic occurrence within a large population over several countries or continents.

Hyperendemic disease

A disease that gradually increases in frequency above the endemic level but not to the epidemic level.

Common source epidemic

An epidemic with a rapid increase to a peak number of infected individuals followed by a rapid but more gradual decline, where cases are reported for approximately one incubation period.

Propagated epidemic

An epidemic showing a gradual rise followed by a gradual decline, with cases reported over a time interval equal to several incubation periods.

Bacteria

Single-celled (unicellular) prokaryote organisms with a primordial nucleus that lack a nucleus and membrane-enclosed intracellular structures.

Archaea

Single-celled prokaryotes with no nucleus that are genetically and metabolically very different from bacteria and are not known to cause disease.

Viruses

Acellular organisms composed of nucleic acid and a few proteins that must enter a cell to multiply.

Viroids

Infectious agents consisting of nucleic acid RNA with a protein coating that cause various plant diseases.

Prions

Protein without any nucleic acid, associated with mad cow disease and related disorders.

Fungi

Eukaryotic organisms containing a nucleus and membrane-bound organelles, which can be unicellular yeasts, mould, or mushrooms.

Protozoa

Large and diverse group of single-celled microscopic eukaryotic organisms with at least one nucleus and numerous intracellular structures.

Helminths

Multicellular eukaryotic animals (parasitic worms) that generally possess digestive, circulatory, nervous, excretory, and reproductive systems.

Reservoir

The habitat in which the infectious agent normally lives, grows, and multiplies.

Source

The individual or object from which the infectious agent is acquired.

Asymptomatic carrier

An individual with a subclinical infection showing no detectable symptoms but capable of transmitting the pathogen to others.

Asymptomatic chronic carriers

Asymptomatic individuals who continue to harbour a pathogen for moths or even years after the initial infection.

Latent viral infections

Occurrences where a viral pathogen becomes dormant in a cell, is not replicated, and displays no symptoms until it becomes active again.

Zoonoses

Animal diseases that can be transmitted to humans through close contact, secretions, or vectors.

Pseudomonas sp.

Gram-negative bacteria commonly found in soil and on plants that are important opportunistic pathogens naturally resistant to multiple antimicrobial agents.

Clostridium sp.

Gram-positive, anaerobic, spore-forming bacteria commonly found in soil.

Clostridium tetani

Bacteria that can be part of the bowel microbiota of animals and produce endospores that remain viable in soil, transferring to humans via contaminated injury.

Clostridium perfringens

Bacteria with widely distributed endospores that can cause gas gangrene through skin breakage or gastroenteritis if ingested in food.

Clostridium botulinum

Bacteria found in soil whose endospores can germinate in poorly preserved food under $AnO_2$ conditions to produce neurotoxins leading to botulism.

Legionella

A pathogen found in natural streams and isolated from the cooling towers of air-conditioning plants.

1. What organism causes cholera?

vibrio cholerae

2. What type of bacterium is Vibrio cholerae?

Gram negative (curve rod shaped Comma shape) motile non spore forming

What toxin causes cholera symptoms?

Cholera toxin (CT / choleragen)

what does cholera toxin do?

Stimulates secretion of chloride ions into the intestine → water follows → severe diarrhoea

what is the primary site of infection for cholera?

the small intestine

What are “rice water stools”?

watery rice colored stool containing mucus and epithelial cells

7. Incubation period of cholera?

6 to 48 hrs

. Main transmission route of cholera?

faecal oral route (specifically via water)

9. Environmental reservoir of Vibrio cholerae?

brackish water estuaries and plankton algae biofilms

Why are floods linked to cholera outbreaks?

contaminate drinking water by disrupting sewage systems

Why do most cholera infections go unreported?

~75% are asymptomatic

3. Major symptom of severe cholera?

profuse watery diarrhoea leading to dehydration and shock

Why is cholera deadly?

massive fluid and electrolyte loss leading to hypovolemic shock

First-line treatment for cholera?

oral rehydration therapy RHS

why is glucose included in ORS?

enhances water sodium and water absorption via co transport

Role of antibiotics in cholera?

reduce duration and toxin load but not essential without infection

Why is sanitation important in cholera prevention?

prevents faecal contamination of drinking water

What is a cholera carrier?

a asymptomatic individual who can still pass on bacteria

21. What does HIV stand for?

Human Immunodeficiency Virus

22. What does AIDS stand for?

Acquired Immunodeficiency Syndrome

23. Structure of HIV?

Enveloped, icosahedral, single-stranded RNA virus

what are the key enzymes in HIV?

Reverse transcriptase, integrase, protease

Function of reverse transcriptase?

converts viral RNA into DNA

Function of integrase?

Inserts viral DNA into host genome

Function of protease?

cuts the viral proteins into functional pieces

main target cells of HIV?

CD4+ T helper lymphocytes

where does HIV originate from?

Zoonotic transmission from chimpanzee SIV in Central Africa

Main transmission routes of HIV?

Blood, semen, vaginal fluids, breast milk, rectal fluids

Why can HIV go undetected early?

Window period before antibodies/viral markers are detectable

Early HIV symptoms (2–4 weeks)?

fever, cough, ash, sore throat, lymph node swelling, fatigue (flu like symptoms)

What happens during latent HIV stage?

slow progression of symptoms, slow CD4+ decline

What defines AIDS?

CD4+ T cell count below 200 cells

Time from HIV infection to AIDS (typical)?

10 years

Example of opportunistic infection in AIDS?

Pneumocystis jirovecii pneumonia

Neurological complications of AIDS?

Encephalitis, meningitis

Respiratory complications of AIDS?

Tuberculosis, pneumonia, lung tumours

Skin-related AIDS complications?

Tumours and lesions

Why does HIV persist for years?

Gradual destruction of CD4+ T cells over time

42. Why is HIV dangerous long-term?

Progressive immune system collapse → opportunistic infections

Why do some people not know they are infected with HIV?

They are asymptomatic and/or unaware due to delayed detection

does vibrio Cholerae form endospores

no they are non spore forming

How is Vibrio cholerae motile?

Single polar flagellum

oxygen requirement of Vibrio cholerae?

Facultative anaerobe (can grow with or without oxygen, grows better with oxygen)

What environments can some Vibrio species tolerate?

• Halophilic (salt-requiring)

• Alkaline tolerant

• Sensitive to acidic conditions

7. How many Vibrio cholerae serogroups exist?

Over 208 serogroups (based on O-antigen)

8. Which serogroups cause human disease?

O1 and O139 only

What are the two biotypes of O1?

Classical and El Tor

What is O139?

A genetic variant of the El Tor biotype

Where was O139 first identified?

Bangladesh (1992)

Primary treatment for cholera?

Fluid and electrolyte replacement

What does ORS contain?

• Sodium chloride (NaCl)

• Sodium bicarbonate (NaHCO₃)

• Potassium chloride (KCl)

• Glucose

Why is glucose included in ORS?

Enhances sodium absorption → water follows by osmosis

17. When are intravenous fluids used in cholera?

In severe dehydration cases

1. What is the chronic/latent phase of HIV infection?

A long period where HIV is present but symptoms are mild or absent, while CD4+ T cells gradually decline

What happens to HIV during the latent phase?

The virus continues to replicate slowly and progressively damages the immune system.

What is thrush and why does it occur in HIV?

Oral fungal infection caused by Candida species due to weakened immune system.

Why do cold sores occur more frequently in HIV patients?

Reactivation of latent herpes simplex virus due to immune suppression.