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Controlling communicable diseases

Vaccination

Vaccinations prevent symptoms of an illness (such as flu or rubella) from developing, by creating a primary immune response to an unharmful substance that the body identifies as a pathogen. This could be an antigen, or the pathogen itself - dead or otherwise modified to prevent disease. Some vaccines are really successful and have prevented many diseases so far, yet the flu vaccine remains a challenge due to the above points. The virus changes its antigens, and there is great variation to start off with.

Booster vaccination is administered (e.g. every 10 years for tetanus) to make up for decreasing immunity over time due to memory cells dying. It boosts the immune response back to levels that confer protection against the disease.

Our natural immunity does not cover certain pathogens such as the flu virus. Vaccination attempts to induce artificial immunity which is an add-on to our natural immunity, by adding an artificially triggered response specific to a new pathogen that we did not have innately.

In the case of rabies, a vaccine is given containing antibodies in order to act as an emergency, passive treatment. Normally, the rabies vaccine would be given preventively to avoid getting the disease, but if someone is likely to have already got infected without prior vaccination, the administration of ready antibodies into their blood can help tackle the illness in its tracks. The antibodies would be obtained from someone else's blood who has already raised an immune response to the pathogen. The passive vaccine of antibodies means that the patient does not need to wait to raise their own immune response, because the antibodies that would need to be made are simply delivered themselves straight into their blood.

Immunisation attempts through vaccination have had varying degrees of success for different diseases. Smallpox is an example of eradication through vaccination, while flu is an example of management and prevention through vaccination, but not long term eradication.

There are ethical considerations surrounding vaccination. On the one hand, large scale vaccination can prevent escalation of epidemics via herd immunity. When more people are immune to a certain infectious agent, transmission from person to person becomes more difficult even when a small number of cases do occur.


Therefore, anyone getting vaccinated would want to ensure others follow suit. On the other hand, the personal decision to get vaccinated can interfere with the goal of achieving a good immunity status for a given population against an illness. Some people would be cautious to get themselves or their children vaccinated due to suspected long term side effects.

The balance of personal autonomy versus achieving greater societal goals that require everyone to synchronise in their decision making has to be accomplished.


HPV vaccination

The Human Papilloma Virus (HPV) covers many different strains, some of which cause warts, and others which are associated with a higher risk of cervical cancer. The cervix is the lower part of the uterus. Mandatory vaccination is described by the NHS as "All girls aged 12 to 13 are offered HPV (human papilloma virus) vaccination as part of the NHS childhood vaccination programme."

Ethical conundrums surrounding HPV vaccination cover "vaccination for boys" to potentially protect against diseases other than cervical cancer e.g. warts and oral cancer; the vaccine being mandatory and the ability of parents to decide for their children; and others.

Some have stated that early vaccination against a sexually transmitted infection would increase sexual activity due to a false sense of being protected, although this has been shown to not be the case. Similarly, concerns regarding a failure to continue getting cervical smears have been expressed. Cervical screening is essential because the vaccine does not provide 100% protection.

Active immunity refers to immunity acquired as a result of an illness. This is also the type of immunity induced via vaccination, as the body is responding in the same way when it encounters the pathogenic antigen and responds appropriately.


Passive immunity is the type of immunity acquired directly via the relevant antibodies rather than by developing them afresh following disease or other ways of contacting antigens. An example is the immunity passed to a foetus via the placenta during gestation.

Biological problems in terms of deploying vaccines include storage, distribution and nutritional status issues.

Public Health England provides vaccine storage guidelines which include only ordering vaccines as needed to avoid storage beyond expiry date, administering them in the order of the expiry date, storing immediately upon delivery in fridges at around 5 °C, monitoring temperature using two thermometers, etc. This is to ensure the vaccine ingredients do not denature, causing potential side effects in patients or being less effective. It is also to make vaccination cost-effective and save millions of pounds a year.

In terms of distribution, quality vaccines must be distributed to those most in need, which requires the orchestration of many international institutions, hospitals and distributors. If the distribution of vaccines for a particular disease fails to be adequate for all parties involved, then prioritisation of vaccine recipients takes place.

The nutritional status of vaccine recipients is important for vaccination outcomes. In some developing areas, and in places such as prisons and refugee camps, nutrition is inadequate in two ways: total calorie-wise, and protein-wise. For vaccination success, energy availability from sufficient calories isn't critical, but sufficient protein intake is.

Therefore, those affected by low calorie intake but with sufficient protein levels (marasmic type) respond adequately to the vaccine, while those low in both calories and protein (marasmic-kwashiorkor type), and those sufficient in calories but low in protein (kwashiorkor) do not respond adequately to the vaccine.


Antibiotics

Antibiotics is one of those technical terms in biology which actually describes its object. ANTI = against, BIOTIC = life. So antibiotics are weapons of mass destruction... sort of.

They are substances which occur both naturally, as well as artificially as made by humans. The reason they are so widespread and important is because they solve a problem humanity has had for a very long time (i.e. forever). They are used to treat bacterial infections. Today that might seem like a small thing, yet around the globe millions of people still die all the time due to bacterial infections (e.g. pneumonia). It's not a small thing, it is one of the greatest medical discoveries.

A one-week course of antibiotics taken orally, for example, can easily treat bacterial infections and the associated disease. This is an amazing achievement. Antibiotics are substances which kill prokaryotic cells, such as bacteria, while leaving eukaryotic cells (in humans and others) untouched. 

Each type of antibiotic targets different things in bacteria. One of the main differences between bacteria and human cells is that the former have a cell wall, while the latter don't. Some antibiotics prevent the formation of cell walls. This renders the bacteria vulnerable to water flooding inside and bursting them. Bursted bacteria can't replicate (really?), and hence the infection ceases. This is called osmotic lysis. Lysis means breaking or disintegration, while osmotic refers to the osmotic effect which results in water flooding into the bacteria, from higher water potential (outside the bacteria) to lower water potential (inside the bacteria).




Penicillin is actually a cell wall-inhibiting antibiotic, naturally produced, and hence discovered from, certain species of the Penicillium fungus. It is of the beta-lactam antibiotic variety, all of which act in the same way to kill bacteria. 

Amongst bacteria, the cell wall composition is a key determinant of what type they belong to. This is important in terms of predicting their response to various antibiotics. Based on different bacteria species' response to crystal violet stain, Gram positive bacteria are able to take up the stain and appear violet under a microscope, while Gram negative bacteria do not take the stain up and will appear pink if a counterstain is added after washing off the crystal violet stain (this will persist in the Gram positive bacteria).

The difference arises because different bacteria have different cell walls. The bacterial cell wall is one of the main targets of antibiotics.



Notice the difference in thickness of the murein layer in gram positive versus gram negative cells. This layer is what absorbs the violet stain. Hence gram positive bacteria turn violet, while gram negative bacteria lose the stain upon washing.

Penicillin is an antibiotic used against gram positive bacteria. It doesn't work on gram negative bacteria because their outer membrane (cell envelope) protects against it. Penicillin works by interfering with the production of the cell wall component murein, and as gram positive bacteria have so much of it and at the outer surface, losing it kills them off. Gram negative bacteria have much less murein and an outer membrane, so penicillin doesn't interfere with their function. Antibiotics that only target Gram positive or Gram negative bacteria are called narrow spectrum antibiotics. Penicillin is one of them.

Antibiotics that actually kill bacteria are called bactericidal. Antibiotics that inhibit bacterial reproduction without killing them directly are called bacteriostatic.

Other ways in which antibiotics target and kill bacteria include interfering with their DNA replication, so they can't replicate further, and interfering with their protein synthesis. This essentially blocks the normal running of their metabolic functions, rendering them dead or unable to replicate.

Tetracycline works this way by preventing protein synthesis. This makes it a bacteriostatic antibiotic. It works by attaching to the small (30S) subunit of the ribosome and hence preventing the tRNA carrying an amino acid from binding. Tetracycline has a binding affinity to both prokaryotic and eukaryotic 30S ribosome subunit, but unlike in humans, the tetracycline in bacteria actually gets pumped into the cell.



This mechanism of action renders both Gram positive and Gram negative bacteria susceptible to tetracycline action. Therefore, this is a broad spectrum antibiotic.

The use of antibiotics is a common example of how evolutionary arms races are critical in the development and deployment of medicines that target organisms. As long as some individuals in a targeted population are able to survive the antibiotic, or in time can develop resistance, under the selection pressure of antibiotic use an ever increasing resistant population will emerge.


This process can happen many times, as organisms are extremely versatile. Bacteria have already been subjected to many natural antibiotic attacks from other organisms (the original penicillin is produced by the fungus Penicillium) so they already have certain resistance genes or pathways they can develop when required.

The key is to understand the adaptation cycle of different organisms and use antibiotics effectively.

1. Not use antibiotics inappropriately, such as to treat colds (caused by viruses not bacteria)

2. Complete prescribed antibiotics treatments so bacteria are effectively killed and there is little to no chance of remaining bacteria coming back stronger

3. Avoid overuse of the same antibiotic in the same setting such as in hospitals where patients are susceptible to infection and spread can be rapid

4. Keep many different antibiotics archived, especially the strongest ones, so that they can be used against multi-resistant strains if they develop, to avoid a situation where no antibiotics are available that bacteria are susceptible to

Strains of Mycobacterium tuberculosis have already posed major challenges due to resistance to multiple antibiotics.

Treatment involves a course of antibiotics which can be lengthy, resulting in many patients stopping at the first signs of amelioration of their symptoms. This causes resistance in the bacteria, which come back to cause disease. Moreover, antibiotic-resistant strains have emerged. There are multi-drug resistant strains which are not affected by the main antibiotics (isoniazid and rifampicin), and even totally drug resistant TB. Managing antibiotic use is crucial to preventing resistance. This includes keeping some antibiotic types as a backup by not using them at all (last resort drugs).

Methicillin-resistant Staphylococcus aureus (MRSA) is an antibiotic resistant form of Staph. that poses particular danger in hospitals as the environment consisting of a very populated area of ill and immune susceptible patients is an opportunity for quick spread. This makes it difficult to treat and eliminate. As its name indicates, this is a form resistant to the antibiotic methicillin.

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