Infectious Disease: Biological And Drug Defences

Microorganisms are small living organisms that you are unable to see without a microscope. They live inside of the host (endoparasites). There are five main types of microorganism’s; bacteria, fungi, protozoa, viruses and parasites. Microorganisms are also known as pathogens and are around us daily, in every environment. There are different shapes and sizes and can survive in various habitats. They can cause disease by attacking and invading the body of their host. Reproducing and causing damage, allows our body to react, increasing our symptoms of infection. They can enter our bodies through cuts or breaks in the skin or by a lumen for example our mouth or genital openings.

Bacteria is unicellular and a prokaryotic cell. They can replace their cells adding to their population, sharing DNA via binary fission. A chromosome divides into two, replicating into identical daughter cells. Our body contains a lot of probiotics that are harmless and beneficial for our bodies to help our immune system fight diseases. Lactobacillus are found in some yogurts and are naturally found in the intestine, they are resistant to digestive enzymes therefore they decrease gastrointestinal problems like irritable bowel syndrome. There are many types of bacteria that can cause different infectious diseases, here are some examples; Spherical shaped bacteria are called cocci, a chain of cocci is known as streptococcus and can cause puerperal fever. Treponema is a spiral formed bacterium that causes syphilis, a sexually transmitted disease. Rod-shaped bacteria are known as Bacilli, this causes salmonella. This is associated with food contamination therefore to prevent having salmonellosis we need to ensure we are following the correct food handling practices for example, keeping raw food away from cooked and using different clean utensils for each. Professionals advise to drink fluids to keep hydrated as this usually lasts around one-week. When the body is under threat by bacteria, it naturally removes the invading cells. It does this by a process called phagocytosis, this is when phagocytes swallow up the infection to prevent illness however bacteria have a capsule, a polysaccharide layer that surrounds the pathogen and protects the cell from being engulfed. This structure allows the bacteria to have more time to invade and reproduce, making it harder for the body to eliminate the cells. Bacteria also have hair like structures on their cell wall, which is composed of protein, this is called Pilus. Pili helps create a strong bond between the bacteria and the host cell. They allow it to attach to surfaces and contaminate, spreading disease.

Fungi are heterotrophs and a eukaryotic organism. There is a variety of fungi E.G. moulds and mushrooms, you can visibly see these with the naked eye however you can only see yeast with a microscope. Most fungi reproduce by creating spores via mitosis and spraying them out, letting them flow freely in the environment. We can inhale spores and due them being tiny they are able to gain access to our lungs, or they can fall on us. If they pass our bodies natural primary and secondary defences, they can cause diseases such as chronic fatigue syndrome or cancer. There are many benefits of fungi, E.G. Yeast is used in bread to make it rise. It is also used in prescription drugs like antibiotics to fight against bacteria’s that is attacking human tissue. Trichophyton is fungi that causes athletes foot and ringworm. Fungus succeeds in warm, moist environments E.G. skin infections are usually in particular parts of the body such as in the groin area, armpits or feet. To prevent athletes’ foot, you should ensure your feet are always clean and dry, wear open/loose shoes. There are also various anti-fungal creams available to treat the infection.

Protozoa are unicellular, prokaryotic cell’s that multiply in their human host cell, causing serious infectious disease. Humans are infected with protozoan that feed from the blood by arthropod vector. There are a number of protozoan, one example; Sporozoa, a complex life cycle that involves both asexual and sexual reproduction. Plasmodium attacks and destroys red blood cells (RBC) in mammals and causes malaria. Protozoa eats Haemoglobin and changes it into Haemozoin, toxic material that causes fever like symptoms such as headaches and aching joints. Each protozoa has pseudopod, this is to allow the microorganism to move around through the bloodstream for maximum invasion.

Viruses consist of nucleic acids. Genetic material replicates new viruses containing information needed to invade the host cell’s DNA. The genetic material is surrounded by a protein coating that penetrates the host whilst protecting genetic material this is known as the capsid. There are numerous types of viruses that are different shapes and sizes. An example of a virus is Acquired Immune Deficiency Syndrome (AIDS) or Human Immunodeficiency Virus (HIV) these diseases are spread when bodily fluid passes through the mucous membrane into our bloodstream during unprotected sex. Once the virus has passed our non-specific defence systems, it attacks our immune system. Our immune system releases clusters of differentiation 4 (CD4) to fight infection and eliminate the virus however viruses also use CD4 to replicate. Transcriptase is an enzyme from CD4 also known as T-lymphocytes helper cells which HIV uses to adapt its RNA into DNA. A drug called Nucleoside reverse transcriptase inhibitors (NRTIs) can prevents the enzyme converting RNA. Protease is also an enzyme however this is to breakdown protein chains which creates the virus, protease inhibitors (PIs) block the enzymes preventing the protein chains from breaking down. HIV has icosahedral or helical structure, the virus is enclosed by a lipid bilayer membrane which forms an envelope surrounding. When viruses are budding, the bilayer is formed. The capsid and envelope are vital for viruses to attach and enter the host cell. They also help with releasing the capsid content to create new viral particles, which helps with the transmitting genetic material from one cell to other cells.

Prions are infectious proteins that gather in the brain and cause permanent damage to nerve cells. This causes brain damage and deteriorates gradually in both humans and animals. An example of the disease caused by prion is Creutzfeldt-Jakob disease (CJD). There is no specific drug that can treat CJD. There has been test done on mice however evidence and research are not strong enough to try on the human body. This disease is not curable and causes the brain to shrink therefore it has been said that once you get symptoms of this disease it is fatal within twelve months.

As well as microorganisms there also can be macro-organisms. These are parasites that are visible and can be categorised as endoparasites or ectoparasites. Examples of macro-organisms are head lice, mites that spreads scabies, tapeworms and ticks that transmits Lyme disease. Ticks that carry the disease thrive in grass and wooded areas. They must be attached to our skin for around 36 to 48 hours to get into our bloodstream. You can prevent being infected by Lyme disease by removing the tick slowly with tweezers and applying antiseptic in the affected are. Lyme disease is caused by bacteria and can be treated by taking antibiotics such as amoxicillin. After treatment, symptoms like aching joints can occur this is known as post-treatment Lyme disease syndrome (PTLDS).

A vector is a living organism that bite their host cell (human or animal) as they need organic material for survival. Vector borne diseases are infections caused by pathogens, vectors only transport the disease they do not have the disease themselves. Once they have bitten you, they infect you with the parasite their carrying, delivering the DNA from the pathogen into the human body. Some examples of vectors are; tape worm, mosquito and houseflies. Vectors transmit various diseases for example houseflies cause dysentery due to the bacteria they carry. Dysentery is a worse case of diarrhoea however pus and blood are present and can cause stomach irritation. It is most known in warm deprived countries like Africa, this is because the parasite can spread easily due to Poor hygiene, for example; people may consume water that is contaminated with human or animal urine and feces. In severe cases medical assistance may be needed where oral dehydration solutions will be provided.

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Another example of a vector is mosquitoes. They are the most common vector and can cause malaria. This is also more common in hotter countries. To prevent this disease, you can receive an appropriate vaccination. A drug called ‘Chloroquine phosphate’ is preferred to treat malaria however most bugs that causes malaria are resistant to chloroquine, therefore will not kill the parasite, allowing it to spread the infection. However, artemisinin-based combination therapies are more reliable as it is more than two drugs that work on the parasite in different ways to ensure it kills the disease. Research states that future treatment is being investigated as the malaria parasite is resistant to the majority of antimalarial drugs.

There are several ways we can transmit disease. The most common way is contact, there are two types, direct and indirect. Direct contact is where an infected person physically touches another person. E.G. sexual contact could transmit genital herpes which is a sexual transmitted infection caused by a virus entering the mouth, genitals or anus. This can be prevented by using contraception such as condoms. Indirect contact is where there is no human contact but contact with contaminated surfaces. Other diseases which can be transmitted are chicken pox, measles and common colds. We can prevent being infected by these diseases by disinfecting areas regularly.

Droplet infection is another way disease can be transmitted. Coughing and sneezing spread microorganisms such as viruses and bacteria which other people inhale. Scarlet fever and meningitis are diseases that are contagious from the droplets. We can prevent these illnesses by covering our mouth and nose when coughing and sneezing and following the recommended hand washing procedure, thoroughly drying to prevent recontamination.

Our body has natural barriers to prevent infectious diseases entering the body. There are two levels of our non-specific defences, these include our external barriers for examples our skin protects the inside of our bodies, obstructing pathogens. If pathogens do enter our bodies passing the external barrier, we also have physical barriers internally for example protease and hydrochloric acid in the stomach help breakdown the illness. If the pathogen is strong enough to pass the first line of our non-specific barrier, we have a second line immune response. This is the complementing system that helps activate the inflammation encouraging phagocytes to attach to the infection (when the pathogen has entered our tissues). Phagocytes are our natural cell eater that destroy the pathogen by eating and removing it from our body.

The specific immune system uses antigens to identify foreign cells. Once they have recognised the cell, they then invade the pathogen and remember the cells to destroy them faster in future infections. T-lymphocytes (T-cells) and B-lymphocytes (B-cells) are white blood cells (WBC) and individually fight a specific antigen. T-cells have receptor proteins on its surfaces. They only have one binding site, Antigens, to create antigen-receptor complexes. B-cells creates immunoglobulin to bind to an antigen.

B cell is stimulated when its attaches Antigen-presenting cells (APC) to a helper T cell, it starts to split. These separating B-cells are known as plasma cells, they secrete antibodies. Proteins attach to the antigens on the pathogen, so macrophages understand it needs to be destroyed.

The immune system consists of antibodies that are produced in the tonsils and thymus. WBC defend our body from infectious disease, fight infection and destroy the pathogen causing it. Bone marrow is containing of connective tissue and lipids. RBC, WBC and platelets are created in the bone marrow and is made up of red and yellow marrow too. This is often be found in long bones like legs.

The lymphatic system transports nutrients and lymph fluids. The lymphatic system is vital for the immune system because the lymph nodes sieve lymph fluid as it passes through collecting pathogens so lymphocytes can destroy them. Damage blood cells are removed from the blood by the spleen which also helps the body cleanse and remove waste products.