Micro Organisms And Infectious Diseases

Types of Microorganisms

Discuss about the Micro Organisms and Infectious Diseases for Infectious Disease.

Microorganisms constitute the majority of the living material of the planet and play a major role in maintaining the ecosystem of the earth. They are either beneficial for the life or can cause harm as well. The main categories of microorganisms include bacteria, virus and fungi. The key features of bacteria include the fact that they are the prokaryotic cells that have the ability to absorb nutrients from their surrounding environment or can produce their own nutrients by the utilization of light energy or other mechanisms. They have plasma membrane and cell wall for protection and possess both RNA and DNA. They use flagella and slimy layer for locomotion (Stowell et al. 2014). Bacteria play a major role in the recycling of nutrients and they can be of three different shapes like rod-shaped, sphere shaped and spiral shaped. Viruses are the obligate intracellular parasites that are made up of a protein coat, capsid or envelope and a nucleic acid that contains either RNA or DNA. Using the machinery of the host cell, viruses multiply inside the host cell (Zhou et al. 2013). The nucleic acid in the virus can be either single or double stranded. Fungi are the eukaryotic cells containing a membrane-bound nucleus and having cell walls. The cell walls of fungi are composed of chitin and they are achlorophyllous. They are heterotrophs and they obtain their nutrients by absorption.

Commensals are the organisms that build up a relationship with another organism in such a way that the former benefits from the latter without affecting it. In this relationship, one organism obtains food and other benefits from the other organism without benefitting or harming the other. Commensals play an important role in the prevention of infections. This is done by denying the entry of the invading organisms to the target site by producing substances that inhibit the growth of the invading organisms and even kills them (Hasegawa et al. 2012). Therefore, the human host can have a variety of benefits from the commensals like cleaner skin, improved digestion and protection from infections. Examples of commensals in the human body are the bacterial species of Moraxella and Neisseria. Pathogens are the microorganisms that are responsible for producing diseases and the diseases that the pathogens cause in human beings are known as pathogenic diseases. Soil contamination has been the most persistent and oldest potential for harboring the pathogens. Pathogens are known to play a variety of roles that include restricting the distribution of plants, regulating the populations, regulating the growth and reproduction of the host and affecting the shelter and food for the animals (Daszak et al. 2015). It becomes easy for the pathogens to move from one species to another when the individuals live close together and therefore, they tend to have a high mortality. Examples of pathogens in the human body are Pseudomonas and Streptococcus.

Pathogenic and Commensal Relationships

Spreading of microorganisms is called as transmission. The process of transmission involves a number of stages that includes escape from the reservoir or host of infection and transporting to the new host. This is followed by the entry to the new host and finally the exit from the new host. Different pathogens have the ability of transmission through various modes. There are various routes of transmission of the microorganisms that includes person-to-person, food, water, insects and fomites. Person to person transmission is occurred by touch, contaminated body fluids and blood, saliva and air. Cold virus can be transmitted by shaking hands whereas HIV and hepatitis B is spread through contaminated blood (Ribeiro and de Oliveira 2012). Flu and cold can spread through the saliva of the infected person on kissing and the diseases like tuberculosis, mumps and measles spread by sneezing and coughing. Harmful microbes can enter the food during the process of production and is transmitted by consumption. The animal and human feces transmit diseases like cholera and typhoid by contaminating the drinking water. Insects like houseflies are responsible for transmitting pathogens to the food like E.Coli and Salmonella and mosquitoes are responsible for transmitting malaria. Fomites are the non-living objects that include toys, towels and bedding that transmits disease-causing microorganisms and the fungus Trichophyton is transmitted through the floors of changing rooms and towels (Smith and Mueller 2015).

The routes of entry to and exit from the human body lead to the transmission of the microorganisms from one host to another. The routes of entry include oral ingestion through food, breakage of skin through the wounds and by touch or contact with sexual transmission of body fluids. Poor processes of food manufacturing and poor processes of food preparation allow the microbes to grow in the food material and therefore lead to the food borne illnesses. E.Coli is a species of bacteria that is often found in the unpasteurized fruit juice and undercooked hamburger meat can have their direct consequences on the elderly and children. Cryptosporidia, Giardia and Salmonella are the microorganisms that infect the water bodies by the fecal matters and can cause diarrhea (Miller and Palenik 2014). Wounds are responsible for breaking the integrity of the tissues and skin through scratches, scrapes and cuts on the superficial layers. Depending on the depth and extent of the wound, the microorganisms infect the wounds that are also mediated by the environment of the wound and the type of microorganism present on the skin. Direct physical contacts as touching and sexual contacts can be responsible for the transmission. Cold virus is transmitted by shaking hands whereas Hepatitis B and HIV is transmitted by sexual contact. Sneezing, coughing, vomiting and excretion forms the routes of exit of microorganisms. These processes release millions of microorganisms in the air as droplets of saliva or mucus and infect the individual whoever breathes in these particles (Mahon and Flaws 2014).

Transmission Routes

Microorganisms are responsible for causing pathological conditions in the human body by entering the body at different sites and causing diseases by various mechanisms. The microbial invasion is countered by the first line of defense, which is followed by the second line of defense. The defense mechanism of the host body consists of natural barriers, nonspecific immune responses and specific immune responses. Natural barriers include the skin, mucous membranes, respiratory tract, GU tract and the GI tract that bars the invading microorganisms. Skin invasion becomes easier for the microbes in case of an injury or surgical incision. The mucous membranes have secretions with antimicrobial properties and contain IgA, IgG and immunoglobulins that prevent the binding of the microbes. Respiratory tract has the filters in the upper airways and GI tract has acidic pH with secretions with antibacterial properties like intestinal secretions, bile and pancreatic enzymes. GU tract acts by producing Tamm-Horsfall mucoproteins that remove the microorganisms (Gallo and Hooper 2012). Nonspecific immune response includes cytokines like interferon-gamma, tumor necrosis factor-alpha, IL-6 and IL-1. These are produced by the activated lymphocytes and macrophages with increased neutrophil production by the bone marrow and by IL-8.  A variety of antibodies like immunoglobulins is produced because of specific immune responses. Antibodies help to eradicate the microorganisms by activating the complement system and gathering the WBCs. By defending all these barriers, the microorganism enters the blood circulation and spreads throughout the body thereby causing the symptoms. 

The reason why not all the microorganisms lead to disease is the effectiveness of the defense mechanism. Infection happens when the microorganisms enter the host body and initiates multiplication. In response to the microbial infection, the immune system comes up with the defense mechanism including the antibodies and the white blood cells. During the process of elimination of the microbial infection from the body by the immune system, various symptoms occur like rash, headache, malaise and fever. However, the secretion of the chemicals like interferon avoids disease due to infection by helping the antibodies to target the invaders (Parham 2014). Apart from the defense mechanism of the body, vaccination can also help to prevent diseases due to infections by creating memory T and B cells that are specific for a particular pathogen. These memory cells act by responding effectively to the repeated pathogenic attacks.

Zika virus generally does not have any signs and symptoms or have only mild symptoms. The commonly observed signs and symptoms of Zika virus are rash, fever, conjunctivitis and joint pain. Associated signs and symptoms include headache and muscle pain. The signs and symptoms usually develop after traveling to a Zika virus prone region. Zika virus is related to the West Nile, Dengue and yellow fever viruses and plays an active role in the development of Microcephaly where a pregnant woman is infected and the fetus develops with a small head and brain (Musso et al. 2014). Complications of neurologic problems and dehydration are the rare signs and symptoms of the infection and the prognosis of the infections involves acute disseminated encephalomyelitis, Guillain-Barre syndrome and eye abnormalities. The treatment of Zika virus infection has not been defined specifically as the disease is mild and no specific treatment is required. Patients suffering from the infection of Zika virus should be provided with plenty of rest with enough intakes of fluids to prevent dehydration (Campos, Bandeira and Sardi 2015). Fever and pain can be treated with the common medicines like paracetamol and acetaminophen and worsening of the symptoms should be dealt with appropriate medical advice and care. Vaccination is not available for this disease and prevention is the best way to keep the disease away.

Campos, G.S., Bandeira, A.C. and Sardi, S.I., 2015. Zika virus outbreak, Bahia, Brazil. Emerging infectious diseases, 21(10), p.1885.

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Gallo, R.L. and Hooper, L.V., 2012. Epithelial antimicrobial defence of the skin and intestine. Nature Reviews Immunology, 12(7), pp.503-516.

Hasegawa, M., Kamada, N., Jiao, Y., Liu, M.Z., Núñez, G. and Inohara, N., 2012. Protective Role of Commensals against Clostridium difficile Infection via an IL-1β–Mediated Positive-Feedback Loop. The Journal of Immunology,189(6), pp.3085-3091.

Mahon, C.R. and Flaws, M.L., 2014. Host-Parasite Interaction. Textbook of Diagnostic Microbiology, p.23.

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