Infectious Diseases

Question 1

What are the 3 major classes of pathogens? Provide an example of each.

Answer 1

Viruses (Influenza)
Bacteria (Prokaryotic pathogens) - M tuberculosis
Parasites (eukaryotic pathogens) - T brucei

Question 2

Able to list some notable pandemics?

Answer 2

Black death - yersinia pestis - 1347-51 - Europe - up to 200mil -
Spanish flu - H1N1 - 1918-20 - World - 50-100mil
2nd cholera pandemic - vibrio cholerae - 1829-37 - World - 50mil

Additional:
Malaria - 2020 - subtropics - 627,000 worldwide - >200mil with disease.

Question 3

Why did infectious diseases claim so many lives in past?

Answer 3

Bad hygiene
Causes mostly unknown -> couldn’t treat
Even if cause known -> lack of treatment options
Lack of knowledge

Miasma theory (until 1850sish) - diseases were caused by “bad air” /”miasma. They originated from environment.

Question 4

What demographics suffer most from infectious diseases?

Answer 4

Neglected tropical diseases: diverse group of communicable diseases prevailing in tropical
and subtropical conditions in 149 countries.
Affect >1bil people and cost developing economies billions of $ every year.

People living under low-income conditions in developing countries are most heavily affected by infectious diseases. Populations without adequate sanitation and in close contact with infectious vectors and domestic animals and livestock.

NTDs include leishmaniasis, dengue, chagas, sleeping sickness, schistosomiasis

Poverty-related infectious diseases = NTDs + Malaria, HIV, TB

Question 5

What’s meant by DALY?

Answer 5

Disability-adjusted life years
1 DALY=loss of 1 year of full health

Considers premature mortality and years lived with disability due to disease.

Question 6

What are some notable advancements in the infectious disease field?

Answer 6

1. MICROSCOPES (Leeuwenhoek)- enabled observation of bacteria, unicellular eukaryotes.
2. GERM THEORY - Diseases caused by microorganisms that invade and replicate within human body. Supported by Koch & Pasteur.
   - Pasteur: no spontaneous generation of living matter. Microbes need living “parent”/ ancestor.
   - Koch postulates:
   Organism always present, in every case of disease.
   Organism isolated from a host containing the disease and grown in pure culture.
   Organism from this pure culture must cause same disease when inoculated into healthy, susceptible animal.
   Organism isolated from inoculated animal and identified as the same original organism first isolated from the originally diseased host.
3. Causative AGENTS began to be identified and presence demonstrated in infected hosts.
4. Some VECTORS identified and mechanisms of TRANSMISSION hypothesised (malaria in mosquito blood meal. Only transmitted by females).
5. DIAGNOSTICS - Differential staining of blood, cells, bacteria for identification.
6. PROPHYLAXIS - protection of rats with diptheria and tetanus toxins.
7. TREATMENT - some dyes kill pathogens. chemotherapy with salvarsan kills syphilis.

Nowadays, we know causative agents of almost all infectious diseases. Drugs, vaccines, diagnostics available for many. We have many methods to study pathogens (MolEpi, bioinformatics, “omics”)

Question 7

List Koch’s postulates

Answer 7

1. Organism/pathogen must be present in every case of disease
2. O/P must be isolated from diseased host and grown in pure culture
3. Organism from pure culture must cause same disease in healthy host when host is inoculated with the pathogen
4. The same organism must now be isolated from the inculated animal and proven to be the same O/P that was isolated in the beginning