Microbial Infection

Question 1

What are the characteristics of viruses?

Answer 1

1. Obligate parasites - can only survive by invading eukaryotic cells
2. Contain RNA or DNA as genetic material
3. Replicate using host-cell nuclear synthetic machinery
4. Show host specificity but infect almost all other life forms, including bacteria
5. Divide/released by budding out of host cell, or cytolysis.

Question 2

What are the modes of infection for viruses?

Answer 2

Faecal-oral, Airborne, Insect vector, Blood borne

Question 3

What are 3 infections caused by viruses and what are their implications?

Answer 3

HIV leads to AIDS and has RNA but it cannot be used by the eukaryote. RNA genome requires reverse transcriptase into DNA before RNA can be used inside the cell. Smallpox is caused by the variola virus. For smallpox vaccine, can deliver it when someone is already infected. Polio causes musculature of the thoracic cavity to be disabled. Oral vaccine now available so easily adminstered.

Question 4

Describe the characteristics of bacteria?

Answer 4

1. Have no internal membranes (photosynthetic bacteria are an exception*)
2. Have a single copy of a chromosome (haploid) while eukaryotes can be haploid or diploid - if there is a mutation it will be instantly expressed (there’s no recessive/dominant gene alleles because there is one copy.
3. Poorly defined cytoskeleton
4. Cell wall contains peptidoglycan (can be used to target) - is the basis of gram stain test and determines shape
5. Divide by binary fission into two daughter cells.
6. Some bacteria are motile - use things like flagella

CHIP BM

Question 5

What are the parts of bacteria?

Answer 5

Nucleoid DNA, Cytoplasm, Ribosomes, Plasma Membrane, Cell Wall, Capsule, Pilus, Flagellum

Question 6

What is the infectious dose and mechanism of action of Shigella?

Answer 6

Infectious dose is around 10-100 bacteria. Faecal-oral route of transmission. Attacks epithelial cells of intestine and spreads from cell to cell, causing death and sloughing of epithelial cells and inducing an inflammatory response resulting in the characteristic dysentery syndrome. Moves within cell but doesn’t have a flagella - uses actin filaments of cytoskeleton to push it from one cell to another. Severe if untreated and can cause a lot of damage. Leads to dysentry with bloody stools.

Question 7

What are the consequences of Neisseria Meningiditis infection?

Answer 7

Commensal so found in epithelium of nasopharynx but not pathogenic. Multiple serogroups are however community acquired. Can be pathogenic leading to formation of non-blanching rash, septicaemia and blood vessel blockage. Infection advances rapidly and if crosses the blood-brain barrier into CSF, becomes meningitis.

Question 8

What are 2 common noscomial infectious agents?

Answer 8

Clostridium difficile in the spore stage and difficult to treat + Methicillin-Resistant Staphylococcus Aureus.

Question 9

What are the strategies used against Mycobacterium tuberculosis?

Answer 9

The condition is difficult to diagnose and treatment takes a long time (6 months). Thus, new drugs to combat anti-microbial resistance and shorter treatment time are available. Better vaccines for adult population in high burder countries and better early diagnosis techniques are also available.

Question 10

In a PET-CT scan of the thoracic cavity, how would inflammation be signified?

Answer 10

PET-CT using 18F-fluorodeoxyglucose (FDG) of thoracic cavity is taken of person with bilateral TB. Orange depicts FDG uptake. If glucose uptake occurs, indicates inflammation.

Question 11

What are the different consequences of infection with Mycobacterium Leprae?

Answer 11

If you get cell mediated immune response: Tuberculoid leprosy which gives skin lesions. If you have up to 5 lesions then you have paucibacillary leprosy; leads to tuberculoid leprosy.
If the body doesn’t give a good cell mediated response then you get a humoral response (antibody driven) which leads to lepromatous leprosy; related to multibacillary leprosy.

Question 12

What is leprosy?

Answer 12

Chronic infection of the skin and nerves. It is transmitted by nasal discharges and has a low infectivity rate and incubation period of 5 years. Can lead to people getting cut and not realizing and then losing digits.

Question 13

What is pathogenic E.coli’s usual mechanism of transmission?

Answer 13

Often a zoonotic infection picked up from animals but can also be released from infected cattle into the food chain.

Question 14

Why do bacteria have more mutations?

Answer 14

Have approximately the same rate of mutation as humans however, have a much shorter generation time of minutes. Cumulatively therefore have more mutations. Moreoever, bacteria only have one copy of genetic material so every mutation is expressed whereas not so in eukaryotes.

Question 15

What are characteristics of fungi?

Answer 15

1. Eukaryotic
2. Cause cutaneous (scalp), mucosal and/or systemic mycoses occur as yeasts, filaments or both
3. Yeasts bud or divide; filaments (hyphae) which have cross walls or septa

Question 16

What is mycosis?

Answer 16

Fungal infection of animals, including humans. Common and often start through inhalation of fungal spores or localized colonization of the skin. May initiate persistent infections; therefore, mycoses often start in the lungs or on the skin

Question 17

What are the characteristics of protozoa?

Answer 17

1. Unicellular, eukaryotic organisms
2. Include intestinal, blood and tissue parasites
3. Replicate in the host by binary fission or by formation of trophozoites inside a cell
4. Divide by asexual reproduction
5. Many have a complicated life cycle involving two hosts
6. Infection is acquired by ingestion or through a vector

UBA2I BIT parasite

Question 18

What are two infections protozoa can cause?

Answer 18

Malaria and Leishmaniasis

Question 19

How is malaria caused?

Answer 19

Malaria is caused by plasmodium. Infection is acquired via a mosquito vector which communicates diseases from one human host to another. Formation of trophozoites inside a cell occurs. People with Sickle-cell and β-thalassaemia are protected as can’t be affected by malaria. Infection depends on the vector. So the pattern of disease depends on the distribution of the vector e.g. The ‘malaria belt’ across the equator which reflects the altitudes at which mosquitoes exist.

Question 20

How is leishmaniasis caused?

Answer 20

Sandfly vector. Is a blood and tissue parasite infection and has a trophozoitic stage. Cutaneous and visceral disease leading to skin lesions and internal organ swelling. Zoonotic where often dogs are the reservoir.

Question 21

What are helminths and their characteristics along with examples?

Answer 21

Metazoa with eukaryotic cells (a whole organism). Are multi-cellular and visible to the naked eye. Life cycles outside the human host - live in soil/water and are picked up. Examples: Roundworms e.g. Ascaris, Flatworms (flukes) and tapeworms.

Question 22

What is the mechanism of infection of helminths and what diseases can be caused by them?

Answer 22

Faecal-oral transmission. Worms in gut lay eggs which are excreted into the environment and are picked up by people e.g. If there is poor water sanitation. Is treatable but no vaccine available. Schistosomiasis is an example.

Question 23

What are the characteristics of schistosomiasis?

Answer 23

Intermediate vector is a snail. Adult worm lives in the hepatic portal vein in humans. They produce spiney eggs which allows them to migrate to the gut. This causes inflammation and swelling. These are excreted and they infect snail. People wash in the water etc. And the cercaria can burrow through the skin and start the process all over again. Can manage through snail management. Basophils are involved in response to parasitic or helminth infections

Question 24

What is Streptococcus pyogenes and how does its infection manifest?

Answer 24

A species of Gram-positive extracellular bacteria that spreads through airborne droplets, shared food and drinks, and direct contact with infected carriers. A Streptococcus pyogenes infection can manifest in multiple ways as rheumatic fever, scarlet fever or Streptococcal pharyngitis.

Question 25

What is the presentation of rheumatic fever?

Answer 25

Inflammatory disease involving the heart, joints, and skin, typically developing a few weeks after a streptococcal throat infection. This occurs due to cross reactive antibodies being produced by the host towards the bacterial antigens that mimic host antigens. Antibodies produced may target cardiac tissue, such as heart valves, resulting in rheumatic heart disease.

Question 26

What is the presentation of scarlet fever?

Answer 26

Characterised by a red rash on the tongue, as well as a sore throat, fever, and swollen lymph nodes. The bacteria produce pyrogenic exotoxin which causes the disease in patients without antitoxin antibodies.

Question 27

What is the presentation of Streptococcal pharyngitis?

Answer 27

Symptoms include fever, sore throat, enlarged and red tonsils and lymph nodes. This is caused by group A streptococcus.