05_biological_agents_20140117153312

Question 1

The main classes of harmful biological agent (micro-organisms) are: 5

Answer 1

 Bacteria  Viruses  Fungi  Protozoa  Macrobial parasites.

Question 2

Bacteria are

Answer 2

living microscopic organisms (typically < 1m), which lack cells with internal membranes. Bacteria contain DNA, but this differs from cellular DNA in that it has a circular arrangement, rather than linear. Bacteria are single celled and can reproduce by duplicating themselves and they do not need a host to survive. Bacteria (for example: tetanus and most forms of pneumonia) are responsive to antibiotics.

Question 3

Bacteria may be classified in a number of ways: 3

Answer 3

 Their need for oxygen for growth. Aerobic bacteria (aerobes) can survive and grow in an oxygenated environment, whereas anaerobic bacteria (anaerobes) do not require oxygen for growth. Anaerobic, bacteria can survive in places where there is less oxygen, such as human intestines and cause gastro enteric illness.  Their reaction to a gram stain test - gram positive or gram negative.  Their morphology or shape

Question 4

A virus is

Answer 4

smaller than one cell. It lives within a cell (intracellular) to survive and derives its ability to multiply from its host cell. Viruses are 20 to 100 times smaller than bacteria and cannot be seen by light microscopy. The largest viruses (poxviruses) are about 450 nanometres in length and the smallest viruses (polioviruses) are about 30 nm. (nm = one billionth of a metre = 0.000000001metre). Viruses are not really ‘alive’ as they cannot reproduce outside of a living cell. They reproduce by transmitting their genetic information from one cell to another. However, they can damage or kill the cells that they infect, causing disease in infected organisms. Some cause cancers by stimulating cells to grow uncontrollably.

Question 5

Antiviral treatments are difficult to create because

Answer 5

of the large number of variant viruses that can cause the same disease. A further concern is the difficulty in disabling a virus without disabling healthy cells.

Question 6

The main BBVs of concern are:

Answer 6

 Hepatitis B virus, hepatitis C virus and hepatitis D virus  Human immunodeficiency virus (HIV).

Question 7

Fungi are

Answer 7

a diverse group of organisms that obtain food by direct absorption of nutrients. The food is dissolved by enzymes that the fungi excrete and is then absorbed through thin cell walls. This is then is distributed by simple circulation, or streaming, of the protoplasm. Fungi may be single-celled or multi-cellular.

Question 8

Protozoans are

Answer 8

living, motile, single-celled organisms that can live inside or outside host cells or organisms. They can only divide within a host organism. Most antibiotics, such as penicillin, don’t work on protozoan diseases. However, they are susceptible to some antibiotics such as sulfonamides.

Question 9

Incubation period

Answer 9

Infection to Symptoms

Question 10

Latent period

Answer 10

Infection to Infectiousness

Question 11

The ‘infectious dose’ is

Answer 11

the amount of pathogen (measured in numbers of organisms) required to cause infection in the host.

Question 12

The variables that can be manipulated to provide (or remove) optimal conditions include: 6

Answer 12

the nutrients available; oxygen levels; water; temperature; pH; and light.

Question 13

Biological infections must be reported to the enforcing authority only when

Answer 13

an employer has been notified by a doctor, in writing, that an employee is suffering from one of the infections listed in Schedule 3 of RIDDOR, which is linked to the corresponding activity.

Question 14

Biological agents are classified into four hazard groups according to: 4

Answer 14

 Their ability to cause infection  The severity of the disease that may result  The risk that infection will spread to the community  The availability of vaccines and effective treatment.

Question 15

The four groups of biological agents and their accompanying descriptions

Answer 15

1 Unlikely to cause human disease. 2 Can cause human disease and may be a hazard to employees. It is unlikely to spread to the community and there is usually effective prophylaxis* or treatment available. 3 Can cause severe human disease and may be a serious hazard to employees. It may spread to the community, but there is usually effective prophylaxis* or treatment available. 4 Causes severe human disease and is a serious hazard to employees. It is likely to spread to the community and there is usually no effective prophylaxis* or treatment available

Question 16

Knowing the HG alone is not sufficient for risk assessment purposes. Although the hazard group of the agent is based on some of its hazardous properties, it is not a complete picture, for example:

Answer 16

it does not address the route(s) of transmission that may influence the risk assessment, in terms of deciding whether additional control measures are required.

Question 17

There are three ways in which you might be exposed to biological agents at work:

Answer 17

1) Exposure as a result of working with biological agents, for example: in a microbiology laboratory. 2) Exposure which does not result from the work itself but is incidental to it, mainly because biological agents are present as contaminants, for example: farming, refuse collection, sewage treatment. 3) Exposure, which is not a result of the work that is done, for example: catching flu from a work colleague. Note: Only the first two categories are covered by CoSHH.

Question 18

Biological organisms have a number of strategies for making the leap to a new host, including:

Answer 18

 Droplet transmission: for example, being passed along when one host accidentally sneezes on another. The flu is transmitted this way.  Airborne transmission: for example, being exhaled by one host and inhaled by another. Tuberculosis is transmitted this way.  Vector transmission: getting picked up by a carrier (the vector, such as a mosquito) and carried to a new host. Malaria is transmitted this way.  Waterborne transmission: leaving one host (in faeces, for example), infecting the water supply, and being taken up (in drinking water, for example) by a new host. Cholera is transmitted this way.  ‘Sit-and-wait transmission’: being able to live outside a host for long periods of time until coming into contact with a new host. Smallpox can survive for years outside of a host.

Question 19

Most micro-organisms have a particular route of entry, but in some cases infection can occur by more than one route. Occupational examples of infection are:

Answer 19

 Putting contaminated hands and fingers (or pens etc.) into the mouth, nose or eyes.  Breathing in small infectious droplets (aerosols) from the air.  Splashes of blood and other body fluids into the eye and other mucous membranes, such as the nose and the mouth.  Broken skin if it comes into direct contact with the micro-organism (or something contaminated by micro-organisms).  A skin-penetrating injury, for example: via a contaminated needle or other sharp.

Question 20

Zoonoses are diseases that:

Answer 20

 can be transmitted from animals to humans  may cause ill health in humans but may not cause ill-health in animals.

Question 21

Human activity is involved with many emerging infectious diseases, for example: environmental change enabling a parasite to occupy new niches or hosts. Several human activities have led to the emergence and spread of new diseases: 4

Answer 21

 Encroachment on wildlife habitats: the construction of new villages and housing developments in rural areas force animals to live in dense populations, creating opportunities for microbes to mutate and emerge.  Changes in agriculture: the introduction of new crops attracts new crop pests and the microbes they carry to farming communities, exposing people to unfamiliar diseases.  Uncontrolled urbanisation: the rapid growth of cities in many developing countries tends to concentrate large numbers of people into crowded areas with poor sanitation. These conditions foster transmission of contagious diseases.  Modern transport: ships and other cargo carriers often harbour unintended ‘passengers’ that can spread diseases to faraway destinations. While with international jet-airplane travel, people infected with a disease can carry it to distant lands, or home to their families, before their first symptoms appear.

Question 22

Hierarchy of control The methods chosen to control the risks identified by the CoSHH biological agent risk assessment should follow the hierarchical approach which is common to both MHSWR and CoSHH. The hierarchy reflects the fact that eliminating and controlling risk by using physical engineering controls is more dependable than relying on systems of work:

Answer 22

 Eliminating risks: for example: by substituting a hazardous biological agent with something less/non-hazardous, such as using a non-toxigenic strain of a biological agent when carrying out laboratory quality control tests.  Controlling risks at source: by using engineering controls and giving collective protective measures priority, for example: using a microbiological safety cabinet when work could create an infectious aerosol, or using needle safety devices to prevent and control needle-stick injuries.  Minimising risks by designing suitable systems of working, for example: having an effective hand hygiene policy in place. This option also includes the use of personal protective clothing and equipment (PPE), but PPE should only be used as a last resort after considering elimination or tackling at source.

Question 23

Any control strategy would include consideration of the following specific hierarchy of control for biological agents: 15

Answer 23

 eradication  reduced virulence  change work method or suppress generation of aerosols  isolation and segregation  containment (CoSHH Schedule 3)  control for specific examples  sharps control  immunisation  decontamination and disinfection  effluent and waste collection  storage and disposal (controlled)  personal hygiene measures  PPE  biohazard signs  baseline testing and health surveillance.

Question 24

Immunisation CoSHH requires that employees should be given a vaccination if the risk assessment shows:

Answer 24

 there is a risk of exposure to a specific biological agent  there is an effective vaccine  the employee is not already immune.

Question 25

Healthcare research laboratory An example of the above measures applied to a workplace setting is a health care research laboratory requiring level 3 containment. The following control measures would be required:

Answer 25

Technical measures  The separation of the laboratory from other activities in the same building.  Extracted air to be passed through a HEPA (high efficiency particulate air) filter.  Access via an airlock to be restricted to authorised persons by means of a security pass or swipe card.  The workplace to be sealable to permit disinfection and to be maintained at an air pressure negative to atmosphere.  All surfaces to be impervious to water, easy to clean and resistant to acids, alkalis, solvents and disinfectants.  Secure storage to be provided for the biological agents.  An observation window to be fitted so that the occupants can be seen at all times.  A class 3 microbiological safety cabinet with sealed front and glove port access to be used to carry out the work.  A facility such as an autoclave to be provided for rendering waste safe.  The provision of appropriate and adequate washing and toilet facilities. Procedural controls  Written procedures for safe handling of potentially infectious samples.  Use of PPE, such as face visors, gloves, etc.  Training.

Question 26

Clostridium difficile (C. diff)

Answer 26

Clostridium difficile (C. diff) is a bacterium that is present naturally in the gut of around two-thirds of children and 3% of adults. C. diff does not cause any problems in healthy people. However, some antibiotics that are used to treat other health conditions can interfere with the balance of ‘good’ bacteria in the gut. When this happens, C. diff bacteria can multiply and produce toxins (poisons), which cause illness such as diarrhoea and fever. Clostridium difficile is an anaerobic bacterium. This means it does not need oxygen to survive and multiply. Therefore, it usually survives well in the large intestine (bowel), where there is very little oxygen. C. diff is not a ‘superbug’ as it lives harmlessly in many peoples’ intestines, and can be treated relatively easily. However, it forms very hardy spores, which can survive for long periods in the environment, for example: on floors and around toilets, and spreads in the air.

Question 27

Escherichia coli (E. coli)

Answer 27

The pathogenic strains include a group of bacteria which are known as Vero cytotoxin-producing E. coli or VTEC. The most important VTEC strain to cause illness in the UK is E. coli O157, which can be found in the intestine of healthy cattle, sheep, goats and other species. Humans may be infected via food or water that has become contaminated by faeces from infected animals. The infectious dose of VTEC O157 is very low at less than 100 bacterial cells. Infection is readily spread between family contacts, particularly those who may be caring for infected children, and in settings such as children’s day nurseries.

Question 28

Farmer’s lung

Answer 28

Farmer’s lung is a noninfectious allergic disease that is caused by inhaling mould spores in the dust from mouldy hay, straw, or grain. This debilitating disease disrupts the normal function of the lungs, where oxygen enters and carbon dioxide exits the bloodstream. Many farmers are forced to leave the occupation due to the physical limitations caused by farmer’s lung. Unfortunately, farmer’s lung cannot be cured.

Question 29

The main BBVs of concern are:

Answer 29

 Hepatitis B, C and D virus, which all cause hepatitis, a disease of the liver (Hepatitis A is not a BBV).  Human immunodeficiency virus (HIV) which causes acquired immune deficiency syndrome (AIDS), affecting the immune system of the body.

Question 30

The word hepatitis means

Answer 30

an inflammation of the liver

Question 31

Leptospirosis

Answer 31

Leptospirosis is a type of bacterial infection that is spread by animals. It is caused by a spirochaetal bacteria called leptospira.

Question 32

MRSA

Answer 32

Methicillin-Resistant Staphylococcus Aureus (MRSA) is a bacterium responsible for several difficult-to-treat infections in humans. It is also called ‘Multidrug-Resistant Staphylococcus Aureus’. The key point about MRSA is that it’s no more aggressive than other infections, but it is more resistant to treatment. MRSA is dangerous because it takes us back to the days when little could be done to stop an infection. The reason hospitals seem to be hotbeds for resistant MRSA is because with many vulnerable patients, infections are common and easily spread. So many different strains are thrown together with so many doses of antibiotics, vastly accelerating this natural selection process.

Question 33

Psittacosis

Answer 33

Psittacines are birds of the parrot family. The terms psittacosis was first used after an outbreak of ‘parrot fever’ in the 1930’s. The bacteria responsible for the infection Chlamydia psittaci, is rife in the general birds population. In other types of birds, such as pigeons, the disease is called ornithosis. In many cities, a large proportion of wild pigeons carry the bacteria. Chlamydia psittaci can remain infective for many months in dried excrement. Birds that have had the disease or are under treatment are fully susceptible to reinfection since the disease does not convey immunity. It’s very infectious and spreads easily, not just to humans, but also to other animals. In wild birds, psittacosis is controlled naturally by the inability of sick birds to keep up with the flock. Additionally, infective droppings fall to the ground below the trees in which the birds perch. The clinical disease that we see in pets is promoted by confining, crowding, transporting, dietary changes, exposure to other infections and forced exposure to infective excrement.