Outcome 2.3 Disease causing organisms Flashcards
Name 2 pathogenic bacteria
Vibrio chloerae and E.coli O157 H7
Name 3 pathogenic viruses
COVID-19, HIV & Influenza
Name 2 pathogenic fungi
Aspergillosis and Dermatomycosis
Name 2 pathogenic protazoa
Plasmodium and Trypanosoma
Describe E.coli O157 H7
- 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
Describe detection of E.coli O157 H7
Culture from faecal samples - E. coli O157- does not metabolise sorbitol, therefore gives different
coloured colonies from other E. coli on this media
Describe treatment of E.coli O157 H7
In severe cases antimicrobial drugs can shorten and eliminate infection. Rehydration is often used to treat patients
Describe prevention of E.coli O157 H7
- Cook meat thoroughly - internal temperature
at least 75oC
Describe Vibrio Cholerae
- 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
Describe treatment of cholera
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.
Describe prevention of cholera
- 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.
Describe HIV
- 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
Describe transmission of HIV/AIDs
AIDS is transmitted by sexual contact or through contaminated blood products (haemophiliacs) or through intravenous drug use
Describe treatment of AIDS
- 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
Describe HIV drugs
- NRTIs and NNRTIs are reverse transcriptase inhibitors
- Protease inhibitors and Entry inhibitors are also used
Describe Human Influenza Virus
- 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
Describe transmission of the Human Influenza Virus
- 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
Describe prevention/treatment of Influenza
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
Describe SARS-COV-2 / COVID and transmission
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
Describe prevention of SARS-COV-2
PPE – Masks/visors, single use gowns, gloves in hospital settings. Physical Distancing Hand washing Lateral flow / PCR testing Mass vaccination
Describe treatment of COVID-19
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.
Describe Dermatocytosis
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
Describe Aspergillusis fumigatus
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
Describe Malaria
Malaria is a disease spread by female mosquitoes and caused by 4 different species of plasmodium (including Plasmodium Malariae).
Describe diagnosis of Malaria
- By taking a blood smear and staining with Giesma stain
- PCR
- Immunologic tests to detect antigens