Diseases and Pathogens Essay

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Diseases and Pathogens


Pathogens are disease-causing or infectious microorganisms (EPA 2011, Kennedy 2012). Some of them are often found in water from sewage discharges, leaking septic tanks, or runoff from feedlots. They enter the body and cause disease every day through the air we breathe, food, water or direct personal contact. The body's immune system is able to destroy many pathogens. When it cannot, infection occurs and the person gets sick. There are different types of pathogens, but the most common are the virus, bacteria, the fungus and protozoa (EPA, Kennedy).

Most Common Types and Their Differences

Bacteria are single-celled microorganisms, which have no nucleus (DHSS 2012, Kennedy 2012). They cause many diseases, many of which can be prevented by vaccination. Bacteria do not usually kill the infected person and only weaken him a lot. These non-fatal bacteria do not spread easily. Examples of bacteria are anthrax, Escherichia coli, salmonella, the streptococcus group, the staphylococcal group, tetanus, gonorrhea and diphtheria (DHSS, Kennedy).

A virus is smaller than a bacterium and a cross between a living and non-living organism (DHHS 2012, Kennedy 2012). It has a RNA or DNA core and an outer protein coat. It attacks the cells of the host or person. There it multiplies rapidly by using the elements of the person's cells. The viral matter destroys, breaks the cell and the new copies proceed to infect other cells. A virus can grow only inside living cells. Examples of viruses are those causing smallpox, the common cold, influenza, herpes and HIV (DHHS, Kennedy).

A fungus is a non-motile micro-organism with filaments and requires organic nutrition for survival (DHHS 2012, Kennedy 2012). Most fungi thrive on dead organic matter. Most of them are considered opportunistic in that they attack when the host body is weakened by another infection or has an open wound or AIDS. This pathogen attacks the skin or hair and causes infections, which are difficult to treat. They are dangerous or fatal when they attack vital organs and the nervous system. Examples of fungi infections are ringworm, jock itch, candidiasis and histoplasmosis (DHHS, Kennedy).

Protozoa are single-celled organisms with defined nuclei (DHHS 2012). Many of them are human parasites, as in the case of malaria, giardiasis and toxoplasmosis (DHHS).

Transmission and Development of Infection

Pathogens can enter the body through any opening (Kivi 2010). It can be a cut in the skin, the lungs, the mouth and the digestive system, the mucous membranes, the eyes and the ears. Pathogens can enter the body if the skin is dirty, broken or has cuts. This is why doctors and nurses wear gloves and use only sterile needles and medical instruments in their practice. Some pathogens are in the air and can be inhaled. The healthy body has nasal mucous that traps these and them expels them. But some pathogens are able to withstand the mucous barrier and enter the lungs. They can enter the body also through the mouth and the digestive system and cause infection through infected foods or drinks. Touching the mouth, biting and licking can also bring pathogens in the air into the mouth. They can also enter the body through the sexual organ, the anus, the eyes or ears. Anything dirty that is placed in any of these organs can transmit pathogens (Kivi).

The development of an infection or invasion by a pathogen begins when it attaches to the cells of the person or host's body (Tunkel 2008). Many pathogens produce toxins or poisons. The pathogen Clostridium tetani does this and causes the tetanus infection. The pathogen multiplies in order to infect. When it does, it defeats the body's natural defenses, causes a chronic infection, or is destroyed and expelled by the body alone or by treatment. Some pathogens can block the body's natural defenses by interfering with the production of natural antibodies, enclosing themselves in outer coats, resisting getting opened by substances in the bloodstream, and producing substances, which deflect the action of antibiotics. Some of them develop resistance to particular drugs (Tunkel).

Viral Infection: the Common Cold

There are more than 200 different viruses believed to be responsible for this infection (WebMd 2007). The most common are the rhinoviruses, corona viruses, and the respiratory syncytial virus or RSV. Rhinoviruses account for 10-40% of all cold infections, the corona viruses for 20% and RSV for 10%. Rhinoviruses are most active in spring,
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early fall and summer and grow best at 91 degrees temperature, which is the temperature of the human nose. Corona viruses, on the other hand, are most active in the winter and early spring. Only 3 or 4 corona viruses out of more than 30 kinds infect human beings (WebMD).

The virus first settles in the nasal epithelium and may remain undetected until the 5th day (Wong 2012). The symptoms of a cold appear only on the third or fourth day. Rhinitis may develop because of the direct cytocidal effect of virus replication or the release of mediators. When infection occurs, humoral response is detected in both the serum and nasal secretions of the person. Serum-neutralizing antibodies are also undetected until 14 days after infection. The peak period for human corona virus infections differs by several months. Group viruses usually follow a cycle with a 2-3-year interval. High infection rates have been observed to be caused by 229E or C43 group as occurring throughout the world (Wong).

The incubation period for the common cold caused by these viruses is short at 2-4 days (Wong 2012). The infection may also be sub-clinical or very mild. Re-infection by the same serotype often occurs within 4 months from just the first infection. Re-infection may also develop with related strains (Wong).

Bacterial Infection: Cholera

Cholera is an intestinal bacterial infection by vibrio cholerae (Sack et al. 2004). The disease is characterized by the loss of large volumes of watery stool, which leads to critical and swiftly progressing dehydration and shock. In the absence of adequate and timely re-hydration therapy, the condition can kill half of all the infected. The cholera toxin, which strongly stimulates adenylate cyclase, induces the intestine to secrete water fluid in volumes beyond the intestinal absorptive capacity (Sack).

It is considered the classic water-borne disease for its close association with water (Sack et al. 2004). The bacterium v cholerae is transmissible by contaminated food when it is mixed with contaminated water as vehicle for infection. Contaminated food, such as undercooked seafood, is the usual medium of transmission, while contaminated water is the more common in less developed countries. Cholera is seasonal. It is endemic in warm countries like Bangladesh at two peaks each year after the monsoon rains. In Peru, it is endemic during the warm season only. The vibrios appear to be capable of rapid growth in warm temperatures. Annual rates of the disease in endemic areas vary widely, often influenced by environmental and climate changes. The most typical symptom is diarrhea. The severity depends on many factors, which include local intestinal immunity, the size of the inoculum ingested, the integrity of the gastric-acid barrier and the person's blood group. Persons of the blood group O. are of much higher risk of severe cholera from El Tor vibrios than other blood groups. The group with the highest attack rates consists of children 2-4 years of age. It is generally detected among adult men because of their exposure to contaminated food and water. The patterns of water use affect the spread of the diseases. In some cities in Peru, for example, the disease spread through the municipal water system, which brought about high levels of infection in the urban areas. In rural areas where drinking water comes from rivers or open wells, disease tends to spread among those living adjacent to and drinking the contaminated water. Secondary sources of infection are funeral events because of unhygienic funeral practices in some countries. A cholera outbreak should be suspected if a person older than 5 years becomes dehydrated or dies from acute watery diarrhea or when there is a sudden rise in such incidence, especially when "rice water" stools, similar to those of cholera, are observed (Sack et al.).

Incubation is between 18 hours to 5 days from ingestion of suspected contaminated water or drink (Sack et al. 2004). The symptoms are abrupt and include diarrhea and vomiting, especially the painless but voluminous stools, which look like "rice water." These are most typical of cholera and have a fishy odor. The vomit is clear, water and alkaline. There is severe dehydration from severe diarrhea. There is low-volume or no peripheral pulse, undetectable blood pressure, sunken eyes, wrinkled hands and feet and pale skin. The patient becomes restless and extremely thirsty. He turns apathetic as the shock condition progresses. He may lose consciousness. There may be metabolic acidosis with gasping breaths. He has no urine output. Rapid fluid loss puts him at the risk of death within a few hours. Death usually occurs on the first day. Insufficient quantities of re-hydration fluids may make…

Sources Used in Documents:


DHSS, 2012. 'Chain of infection,' Principles of Infectious Disease Epidemiology,

Department of Health & Senior Services, [Online] Available at http://health.ml.gov/training/epi/DiseaseProcess.html

Earthtym, 2012. 'Ringwor fungal infections, 'Earthtym, [Online] Available at http://www.earthtym.net/ref-ringworm.htm

EPA, 2011. 'Pathogen Information,' Information Collection Rule: U.S. Enviromental

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