Infectious Diseases and Antibiotics

Terminology and definitions covering infectious diseases (cholera, malaria, HIV/AIDS, TB) and the mechanisms/consequences of antibiotics and resistance.

Infectious diseases

Diseases caused by organisms known as pathogens, which can be passed from infected to uninfected people.

Pathogen

An organism that causes disease, such as a protoctist, bacterium, or virus.

Disease transmission

The transfer of a pathogen from a person infected with that pathogen to an uninfected person via direct contact, air, water, or animal vectors.

Disease carrier (carrier)

A person infected with a pathogen who shows no symptoms but can be the source of infection in other people.

Transmission cycle

The passage of a pathogen from one host to another that is continually repeated as the pathogen infects new hosts.

Disease eradication

The complete breakage of the transmission cycle of a pathogen so that there are no more cases of the disease anywhere in the world.

Endemic disease

A disease that is always present in a population.

Incidence

The number of people who are diagnosed with a disease over a certain period of time, such as a week, month, or year.

Prevalence

The number of people who have a specific disease at any one time.

Epidemic

A sudden increase in the number of people within a population who have a disease.

Pandemic

An increase in the number of disease cases throughout a continent or across the world.

Mortality rate

The number of deaths over a particular length of time, usually expressed per $100000$ people per year.

Vibrio cholerae

The bacterium (prokaryote) that acts as the causative agent for cholera.

Choleragen

A toxin secreted by $V.\text{ cholerae}$ in the small intestine that disrupts epithelium function, leading to the loss of salts and water into the gut.

Oral rehydration therapy

A treatment for cholera involving a solution of salts and glucose used to rehydrate the body and maintain osmotic balance.

Disease vector

An organism, such as the female Anopheles mosquito, which carries a pathogen from one person to another or from animal to human.

Plasmodium

The genus of protoctist (eukaryote) responsible for causing malaria, including species such as $P.\text{ falciparum}$ and $P.\text{ vivax}$.

Prophylactic drug

A preventative drug, such as chloroquine or proguanil, taken to stop an infection from occurring.

Artemisinin-based combination therapy (ACT)

The current best treatment for malaria, especially species $P.\text{ falciparum}$, utilizing drugs derived from the plant $Artimisia\text{ annua}$.

HIV (Human Immunodeficiency Virus)

A retrovirus with RNA genetic material that infects and destroys T-helper lymphocytes of the immune system.

AIDS (Acquired Immunodeficiency Syndrome)

A collection of opportunistic diseases caused by the immunodeficiency resulting from HIV infection.

Retrovirus

A type of virus, like HIV, that uses the enzyme reverse transcriptase to convert its viral RNA into DNA inside a host cell.

Reverse transcriptase

An enzyme found in HIV that uses viral RNA as a template to produce DNA once the virus has entered a host cell.

Opportunistic infection

An infection caused by pathogens that take advantage of a host with a weakened immune system, such as oral thrush or Kaposi's sarcoma.

T-helper lymphocytes

Cells of the immune system that control the body's response to infection and are the primary site of action for HIV.

Mycobacterium tuberculosis

One of the two primary bacteria that cause tuberculosis (TB) by infecting human cells, particularly in the lungs.

DOTS (Direct Observation Treatment, Short Course)

A WHO scheme where health workers or family members ensure patients take their TB medication regularly for $6$ to $8$ months.

MDR-TB (Multiple-drug-resistant TB)

Strains of $M.\text{ tuberculosis}$ that are resistant to at least the two main first-line drugs, isoniazid and rifampicin.

XDR-TB (Extensively drug-resistant TB)

Strains of TB resistant to first-line drugs and the specialized drugs used to treat MDR-TB.

BCG vaccine

The only vaccine currently available for TB, derived from $Mycobacterium\text{ bovis}$.

Antibiotic

A substance derived from a living organism that is capable of killing or inhibiting the growth of a microorganism without harming human cells.

Peptidoglycans

Long molecules containing peptides and sugars that form the structural cross-links in bacterial cell walls.

Penicillin

An antibiotic that inhibits the enzymes responsible for building cross-links between peptidoglycan polymers in bacterial cell walls.

Autolysins

Enzymes secreted by growing bacteria that create small holes in the cell wall to allow it to stretch and link new peptidoglycan chains.

Antibiotic resistance

The ability of bacteria or fungi to grow in the presence of an antibiotic that would normally inhibit or kill them, often arising by mutation.

B-lactamase (penicillinase)

An enzyme produced by some bacteria that catalyses the breakdown of penicillin, rendering the antibiotic ineffective.

Plasmids

Small loops of double-stranded DNA in bacteria that often carry genes for antibiotic resistance and can be transferred between cells.

Conjugation

A process where a tube forms between two bacteria, allowing the movement of DNA, such as plasmids, from a donor to a recipient.