Outcome 2.3 Disease causing organisms

Question 1

Name 2 pathogenic bacteria

Answer 1

Vibrio chloerae and E.coli O157 H7

Question 2

Name 3 pathogenic viruses

Answer 2

COVID-19, HIV & Influenza

Question 3

Name 2 pathogenic fungi

Answer 3

Aspergillosis and Dermatomycosis

Question 4

Name 2 pathogenic protazoa

Answer 4

Plasmodium and Trypanosoma

Question 5

Describe E.coli O157 H7

Answer 5

• E.coli is gram ne gative and rod shaped
• Many strains of E.coli are non-pathogenic
• E.coli O157 H7 produces two exotoxins, these two exotoxins resemble exotoxins found in Shigella dysenteriae (Verotoxins).
• Symptoms range from mild diarrhoea to severe bloody diarrhoea known as haemorrhagic colitis.
• The infection can also result in haemolytic uremic syndrome, in which renal failure occurs. The mortality rate is 1%
• The reservoir is the intestines of healthy cattle and other ruminants
• The bacterium is extremely virulent- <100 bacteria are
  required to cause a productive infection in a healthy person
• Butchered cattle can be contaminated through contact with intestinal contents at slaughter. Undercooking of the resultant meat or poor hygiene spreads the infection to humans

Question 6

Describe detection of E.coli O157 H7

Answer 6

Culture from faecal samples - E. coli O157- does not metabolise sorbitol, therefore gives different
coloured colonies from other E. coli on this media

Question 7

Describe treatment of E.coli O157 H7

Answer 7

In severe cases antimicrobial drugs can shorten and eliminate infection. Rehydration is often used to treat patients

Question 8

Describe prevention of E.coli O157 H7

Answer 8

• Cook meat thoroughly - internal temperature

at least 75oC

Question 9

Describe Vibrio Cholerae

Answer 9

• The causative agent of cholera
• Transmitted by the fecal-oral route through fecally contaminated water
• The infective dose is between 10^3 and 10^8 vibrio bacteria and depends on stomach acid – the more acidic the stomach is the greater the infective dose required
• The bacteria multiply in the intestine and cause a severe watery diarrhoea with sudden onset
• The Vibrio cells attach to the intestinal
  cells and then releasing the cholera toxin

Question 10

Describe treatment of cholera

Answer 10

The treatment for cholera is Oral Rehydration Therapy where the fluid that is lost is replaced. In some cases intravenous rehydration therapy is required.

The aim is to replace the water and electrolytes lost from the body.
Antibiotics e.g. streptomycin are sometimes prescribed and they can shorten the course of cholera but alone they provide no cure as the dehydration must also be treated.

Question 11

Describe prevention of cholera

Answer 11

• improved hygiene and access to clean drinking water supplies
• An oral cholera vaccine is available and this
  provides some protection for a limited time following immunisation. It offers around 90% protection against cholera for 4-6 months. Regular boosters are therefore required to provide adequate immunity.

Question 12

Describe HIV

Answer 12

• The Human Immunodefiency Virus is a retrovirus and the causative agent of AIDs.
• The enveloped virus contains glycoproteins on its envelope surface which bind to cells and cause fusion with the viral envelope.
• Reverse transcritptase converts the viral RNA into DNA and the DNA is incorporated into the cells genome where it remains latent for many years
• HIV invades macrophages and CD4 T-cells
• Destruction of the CD4 T-cell leads to crippling of immune responses which leaves the host susceptible to other secondary infections.
• When blood CD4 T-cell numbers fall below 200/μl of blood, the symptoms of AIDS appear

Question 13

Describe transmission of HIV/AIDs

Answer 13

AIDS is transmitted by sexual contact or through contaminated blood products (haemophiliacs) or through intravenous drug use

Question 14

Describe treatment of AIDS

Answer 14

• Safe sex and using clean needles are the only viable preventative strategies at present
• Drugs are used to treat the secondary infections.
• Producing a vaccine is difficult because the virus mutates rapidly

Question 15

Describe HIV drugs

Answer 15

• NRTIs and NNRTIs are reverse transcriptase inhibitors

- Protease inhibitors and Entry inhibitors are also used

Question 16

Describe Human Influenza Virus

Answer 16

• Influenza belongs to the orthomyxovirus family.
• These are enveloped single-stranded RNA viruses. The lipoproteinenvelope is covered in protein spikes.
  Two glycoproteins make up the spikes
  neuraminidase (N)
  haemagluttinin (H)
• The neuraminidase is an enzyme which hydrolyses the mucous coating of the respiratory surfaces.
• Hemagglutinin, is a glycoprotein that causes red blood cells (erythrocytes) to agglutinate, or clump together.

Haemagluttinin binds to a carbohydrate molecule on the surface of mammalian cells.
The virus replicates within respiratory epithelia and
emerges budding from the host membrane taking a piece of membrane – which forms the viral envelope- with it.
Together these two proteins contribute to the virulence of the virus.

The genome of the virus is known for its variability.
Mixing of viruses occurs in areas where animals and
humans live in close proximity

Question 17

Describe transmission of the Human Influenza Virus

Answer 17

• Influenza is transmitted by droplet infection and more
  effectively infects cells of the lower, than the upper
  respiratory tract
• The virus attaches to epithelial cells via sialic acid receptorsby binding of the H protein
• After infection, leucocytes infiltrate and the cytokines
  released by them give rise to the chills, malaise, fever and aches in muscles. Severe damage to the epithelial cells can allow secondary infections in and can cause pneumonia and bronchitis

Question 18

Describe prevention/treatment of Influenza

Answer 18

Vaccination
Antiviral drugs (amantadine and rimantadine can give some protection against type A viruses
Antiviral drugs (amantadine and rimantadine can give some protection against type A viruses

Question 19

Describe SARS-COV-2 / COVID and transmission

Answer 19

Virus named SARS-CoV-2 and the disease it causes was termed COVID-19
Strucutre - Enveloped, positive sense single stranded RNA virus
In SARS-CoV-2 spike proteins are made up of 2 glycoprotein subunits (S1 & S2)
S1 protein in virus envelope binds to Angiotensin-converting enzyme 2 found in the cell membrane of epithelial cells in the lungs
The viral genome is released and the cell makes multiple copies of the viral particles

Question 20

Describe prevention of SARS-COV-2

Answer 20

PPE – Masks/visors, single use gowns, gloves in hospital settings.  
Physical Distancing
Hand washing
Lateral flow / PCR testing 
Mass vaccination

Question 21

Describe treatment of COVID-19

Answer 21

Vast majority will require no treatment – over the counter medications like paracetamol will help with symptoms.

Supportive therapy e.g. Oxygen therapy or dexamethasone to help dampen immune response.

Question 22

Describe Dermatocytosis

Answer 22

Is a term encompassing infection of the skin, nails or hair caused by several types of fungi which live in the skin (dermatophytes). Trichophyton is one causative agent of Dermamycosis, causing tinea infections
such as tinea capitis (ringworm of the head); tinea
pedis (athletes foot).

Ringworm consist of local inflammatory reactions
to Trichophyton due to infiltration.

In rare cases such as in those immunocompromises it can cause dermatophyte abscess in deeper skin layers or even disseminate to internal organs

Question 23

Describe Aspergillusis fumigatus

Answer 23

Aspergillus fumigatus is a fungus and the causative agent of the disease Aspergillosis.
It grows on plants, soil, rotting vegetable matter, household dust, building materials, and food items.
Transmission occurs through inhalation of airborne conidia (spores).
Symptoms of the disease include; shortness of breath, a cough, coughing up blood or lumps of mucus, wheezing, a high temperature (above 38 degrees) and weight loss

Question 24

Describe Malaria

Answer 24

Malaria is a disease spread by female mosquitoes and caused by 4 different species of plasmodium (including Plasmodium Malariae).

Question 25

Describe diagnosis of Malaria

Answer 25

• By taking a blood smear and staining with Giesma stain
• PCR
• Immunologic tests to detect antigens