Infectious And Communicable Diseases From Bacteria Biology Essay


Infectious diseases or 'communicable diseases' are those caused from pathological microorganisms including bacteria, viruses, fungi, parasites, prions, etc, which can spread from one person to another by direct or indirect means. Infectious diseases can also spread from animals to man or vice-versa (WHO, 2010). Throughout history, microorganisms, the causative organisms for infectious diseases have been playing an active role. Many native populations during the middle Ages have been destroyed by plagues. The Europeans when tried to conquer Australia, Africa and Americas had initially used microorganisms to destroy the native populations. However, the infectious diseases have had a serious effect on the fauna and flora. There were huge causes of morbidity and mortality, but in the 20th century developed nations had lower rates of morbidity and mortality from infectious diseases. The major reasons why there was control over the infectious diseases during the later part of the 20th century was due to the development of antibiotics, eradication of small pox through vaccination, improvement in the living conditions and sanitations, etc. However, in the developing nations, infectious diseases are a major cause of death. In the year 1993, about 51 million people died, out of which 16.4 million about 35% were from infectious diseases. In the sub-Saharan African regions about 70 % of the worldwide infectious disease deaths occur. Developed nations account for 10% of the worldwide infectious disease deaths (Wilson, 1995).

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Today, serious changes are made with the environment of the earth such that certain propulsions and groups are becoming vulnerable to certain infectious diseases. Not only have antibiotics made it easier to fight microorganisms but the abuse of the same has resulted in the microbes developing resistance. Besides, many insect vectors are becoming more and more resistant to various pesticides being used. Today there are several emerging infectious such Ebola, H1N1, H5N1, Lassa fever, etc, due to the changing environmental circumstances. In the year 1993, more than 400000 people from Milwaukee US were affected with the epidemic of cryptosporidiosis. In the Southwest people died from pulmonary disease caused due to Hantavirus infection. Not only are the humans affected with infectious diseases but also various other species of domesticated and wild animals (Wilson, 1995).

With History, major changes have undergone with respect to the infectious disease map of the world. In the 20th century, many diseases have spread from tropical to temperate regions and have crossed marine barriers including the Atlantic and the Pacific Ocean. More than 14.2 million people each year die from infectious diseases. On the other hand, heart disease kills about 10 million people each year. The most common infectious disease killer is acute respiratory infectious with 3.7 million deaths each year, followed by HIV/AIDS with 2.8 million deaths, diarrheal group of diseases with 1.7 million deaths, malaria with 1 million deaths and measles with 0.8 million deaths. As sanitation and poor living conditions can increase the risk of infectious diseases, such problems are more common in the lower socioeconomic groups. The WHO has predicted that during the next ten years that infectious disease would reduce by about 3 % due to improvement in the living conditions (Bonita, 2006). In the ICD-9 Listing, codes 1 to 113 are given infectious and parasitic disease codes. It is found that about 83% of all deaths from infectious diseases are from range of symptoms outside the classical ICD mentioned criteria (Norman, 1998).

With a number of infectious such as diphtheria, chicken pox, measles, feco-oral infections, cholera, rotavirus infection, etc, seasonal variations play a vital role, in the temperate and the tropical regions of the world. The mechanism by which this is occurring is not understood clearly. Certain reasons may be applicable for the seasonal variations of a disease:-

Seasonability has several factors and a lot depends on local factors

Depending on the characteristics of the infections epidemics or peak in incidences can occur at different times of the year

There may be an interaction of pathogens that may affect the spread of another infection

Hence, depending on these criteria vaccination can be used to block the spread of the infection (Nicholas C. Grassly, 2006).

Infectious diseases may not just involve one person or a particular community or a population. Often more than one population may be affected across a region or a nation. Besides, infectious diseases can also affect animals including goats (Echinococcus), dogs (rabies), birds (H5N1), etc.

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The listing of the ICD-9 Codes for Infectious diseases includes:-

Intestinal Infectious Diseases - 001 to 009

Tuberculosis - 010 to 018

Zoonotic Bacterial Infectious - 020 to 027

Other bacterial Infectious (such as leprosy, diphtheria, scarlet fever, etc) - 030 to 041

HIV - 042 to 044

Poliomyelitis, kuru, CJD, etc - 045 to 049

Virus with exanthema - 050 to 059

Arthropod borne virus infection - 060 to 066

Other diseases caused by virus and Chlamydia (such as hepatitis A, B & C, rabies, trachoma, warts, etc) - 070 to 079

Rickettsia and other arthropod infections (080 to 088)

Syphilis and other venereal diseases (gonorrhea, urethritis, etc) - 090 to 099

Other Spirochete infections such as yaws, pinta, etc - 100 to 104

Mycoses or fungal infectious - 110 to 118

Helmenthic or worm infestation - 120 to 129

Other infections - 130 to 136

Late effects of infections - 137 to 139 (ICD-9 codes)


Infectious diseases are transmitted by two means, namely the direct and indirect means. Direct means includes contact with the infected person who comes in contact with the normal person. Through contact, infections can spread by three means, the first two include horizontal means and the third include vertical transmission. Infectious diseases usually spread by direct transfer of the infected fluids or secretions from one individual to another. There may be several means of person to person transmission including sharing infected needles, sexual contact, kissing, blood transfusion, sneezing, coughing, mucosa to mucosa, etc. Direct contact would also include contact with infected animals or handling contaminated animal wastes. The vertical transmission is by means of the infected mother to the baby. Infections again can be transmitted by different means at different periods. When the unborn baby is in the uterus, it can get infected from the mother. Certain infections can be transmitted across the placenta and include bacteria (such as syphilis, listeriosis), viruses (such as CM Virus, AIDS, German measles), and protozoans (such as toxoplasmosis) (Lee Goldman, 2007). The effect on the fetus may range from fetal infections, lesions, mental retardation, physical growth retardation, multi-organ defects, birth defects, aborted, etc (Dorak, 2009). On the other hand, infection can spread to the baby during passage of the baby through the infected birth canal. Lastly, infection can spread through contaminated breast milk of the mother during nursing (Lee Goldman, 2007).

Exposure to the infectious agents can result in various outcomes including no infection, clinical infection, sub-clinical infection or carrier status. Clinical infection can result death, carrier status and further immunity or no immunity against the disease. Sub-clinical infection can result in carrier status, immunity or no immunity against the disease (Dorak, 2009).

Infectious diseases can also spread through indirect methods which include contaminated objects, personal items, food borne, waterborne, vector borne, air-borne, ting-borne and surfaces. For example, common cold can spread by using contaminated towels. Various bacterial, viral and parasitic infections can spread through vectors or carriers such as mosquitoes, fleas, lice, ticks, etc. Infectious diseases can also be transmitted from one individual to another through contaminated food or water or the oro-fecal route. Consuming uncooked, undercooked or raw foods, unsuitable drinking water, etc, can cause infectious. For example, in Latin America, there is evidence through PCR diagnostic tests that H. pylori cause gastric problems (Lee Goldman, 2007).

Certain individuals may be at a higher risk of getting infected which includes those with autoimmune disorders, those who have undergone an organ transplant and are taking immunosuppressant, those consuming corticosteroids and those infected with HIV/AIDS. The other risk factors that play a role in the development of the infectious diseases may include age, race, sex, socioeconomic status, geo-location, medication use, illegal drug use, history of travel, etc (Sherwood, 2004). The mode of causation of an infectious disease is by an interaction of internal factors and environmental factors.

An infection may arise as a result of a triad of factors affecting the system including the host, agent and the environment. The host factors include age, sex, gene-type, mental makeup, nutritional makeup, immune status, and health makeup. The environmental factors include air, water, sanitation, psychosocial status, geography, housing, food, healthcare delivery system, etc. The agent factors include pathogenicity of the organism (ability to cause disease), infectivity (ability to cause infection), virulence (ability to cause death), immunogenicity, survival and antigenic capabilities (Dorak, 2009).

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The entire natural cycle of the infection would ensure that the infectious agent is at the business end. The infectious agent would enter the host or reservoir and then exit from the body, carried by a mode of transmission and enter another person's body. It would result in infection in a susceptible host.

Koch bought out certain postulates for infections. In each case, the organism is present. The organism can be isolated or grown in each culture. Once each individual is exposed to the agent, the disease as such can be reproduced. From each of the infected individuals, the pathogen can be isolated.


An individual suffering from an infectious disease may present with no symptoms, symptoms which are not definitive, mild symptoms, or serious symptoms with complications. The period between the exposure of the individual to the infectious organism and the appearance of the first symptom may vary from a few days (in the case of chicken pox, malaria, etc), months to a few years (in the case of HIV). Infectious disease can produce a range of symptoms including:-


Chills and rigors

Bleeding of the gums and periodontal diseases


Sore throat



Body pain

Dyspnea and breathing problems


Fever with seizures

Swelling or a rash


Enlargement of the regional lymph nodes along with tenderness

Diarrhea and dysentery

Bloody stools

Yellowness of the skin and the tongue


Skin lesions or skin rash

Blood shot eyes (in the case of conjunctivitis)

Burning sensation whilst passing urine

Abscess or a draining sinus

Pain, swelling from the affected site along with a rise in the temperature


Spread of the bacteria, along with the toxin in the blood


The diagnosis of Infectious disease is made based on the history, physical examination, signs, symptoms, analysis of the tissue samples, microscopy, culture, blood tests, urine tests, molecular diagnosis and other methods. The history includes details of the personal history, history of travel, family history, social history, occupational history and epidemiology (Paul G. Engelkirk, 2007).

Body samples of urine, CSF, nasal secretions, nasal swab, stools, etc are collected to study them microscopically. In certain circumstances water, soil, inanimate objects and food samples are also analyzed. In certain circumstances the samples are collected at a particular period of time. In malaria, the samples are collected when the fever is high and in the case of typhoid the blood samples are collected when the fever begins to rise. It is important to prevent contamination of the sample during testing and avoid any destruction of the causative organisms. It is important to transport the samples appropriately and test them immediately as many anaerobic species may not be able to survive in the oxygen-rich environment. Besides, it is also important to prevent drying of the samples. All samples should be given appropriate care during laboratory testing as they are hazardous and can infect the testing personnel (Barbara A. Bannister, 2000).

There are different microscopes that can be used for studying the samples including light microscope, phase-contrast microscope, dark-field microscope, electron microscope, etc. Various staining procedures may be required to study the samples including gram staining, Giemsa staining, Ziehl-Nielsen staining, Indian Ink staining, etc. Helminthes, urine bacteria and fecal protozoan are best viewed through direct microscopy of unstained samples. Gram staining helps to identify organisms in pus, CSF, ascitis, pleural fluids, etc. Ziehl-Nielsen staining is used to study that will not stain through ordinary procedures. Romanowsky staining is used to stain blood cells, whereas Giemsa staining is used to identify the parasites present in blood. Immunofluorescence is a method of identifying the organisms through reactions with antibodies tagged with fluorescence dyes. There are two methods of immunofluorescence including direct and indirect methods (Barbara A. Bannister, 2000).

Culturing involves growing the microorganisms present in the sample in the laboratory on an appropriate media and recognizing the same using physical, biochemical and morphological means. Different media may be used including enriched media, selective media and indicative media. Another process of distinguishing between the various strains of an organism is typing. These include biotyping, auxotyping, serotyping, phagetyping, PCR typing, etc (Barbara A. Bannister, 2000).

Blood tests called as 'serological tests' are done to determine the antigen-antibody reaction that occur. Some of the common tests that are done in the laboratory include agglutination, fluorescent antibody tests, radioimmunoassay and ELISA. Molecular methods of diagnosis are used to determine specific DNA fragments that would be a signature of certain species of pathogens. Some of the common molecular diagnostic techniques include PCR and amplification techniques (Barbara A. Bannister, 2000).


One of the earliest ways of managing an infectious disease was in malaria when certain local communities used cinchona to treat the disease. From the cinchona bark, quinine was extracted and is used even today to manage malaria. Today, antimicrobial agents are being used to treat infectious disease. These microbial agents attack the various metabolic pathways that are present in the microbial metabolism. For example certain compounds are similar to PABA, and prevent PABA from undergoing transformation into dihydropteroic acid, which is essential for folate metabolism. Once there is shortage of folic acid in the body, the DNA of the bacteria undergoes degradation. Further other antimicrobial agents which target other portions of the metabolism can also be used for more effective treatment of infectious diseases. These include trimethoprin and sulphamethoxazole. The other ways by which antimicrobial agents act include causes the destruction of the bacterial cell wall, inhibition of the protein synthesis in bacteria, and damaging the DNA structure. For certain antimicrobial agents to act, the bacteria should be sensitive to the drug. Besides, the manner in which the drug is administered and the spectrum of action of the drug also plays a vital role in treating infections. Antimicrobial sensitivity tests are conducted to determine which particular agents the bacteria would be sensitive and resistant to and accordingly select a potent agent to treat the infection (Barbara A. Bannister, 2000). To ensure that the treatment with antibiotics is working properly certain monitoring strategies may be required including:-

Appropriate levels of antibiotics are present in the serum

The levels of antibiotics do not reach a level such that it would cause toxic effects

Patient compliance and adherence

Appropriate means of administration

Pharmacokinetics of new drugs

Monitoring all the adverse effects (dose-dependent or idiosyncratic)

Some of the common groups of antimicrobial agents that are used to treat infections include:-


Penicillinase resistant penicillin

Ampicillin-like agents

Beta-lactamase inhibitors





Antifungal Agents

Antiviral agents

Antimalarial agents

Antitubercular drugs

Antiprotozoan agents


Infectious diseases are transmitted from one individual to another through several routes including direct contact, inhalation of airborne infections, consuming contaminated food or water, through vectors such as mosquitoes, ticks, etc, sexual contact, using contaminated personal items and through the mother-fetal route. Hence, prevention can be advocated by obstructing the means of transmission of the infection. One of the most important methods of prevention is by proper and frequent hygiene by handwashing and using a disinfecting soap. Immunization also plays a vital role in preventing infections by administering vaccines to the general populations. Vaccines are currently available for a number of bacterial and viral infections including meningococcal infections, hepatitis B, hepatitis A, polio, diphtheria, typhoid, tetanus, haemophilus influenza, chicken pox, rotavirus, human papilloma virus, H1N1, measles, mumps, rubella, etc. Passive immunization can be administered by the administration of immunoglobulin. Zoonotic infections can be prevented by immunizing the pets, providing a clean and safe environment for the animals, washing hands before contacting animals, takes measures after animal bites, etc. At the workplace, transmission of infections are a risk because of the conditions and also because people are in close contact with each other and also with hazards. Needles, syringes and other biohazards need to be disposed off properly. Blood during donation and infusion should be appropriately screened for various blood-borne infections such as HIV, Hepatitis B, hepatitis C, syphilis, etc. Rubber gloves should be worn by the healthcare professional and for every new patient, a new set of sterile drugs should be selected. Hospital wastes should be disposed off properly to prevent hazardous wastes from further causing havoc (Andi L. Shane, 2008).

Safe sex and sexual hygiene is also essential to prevent risk of transmission of STD's such as HIV, hepatitis B, etc. If there is the chance of the partner practicing unsafe sex, then a condom and other barriers help reduce the risk of transmission. Special precautions also need to be taken during travel. Areas infected with infectious diseases should be best not visited. For some people, vaccination may be required along with consumption of prophylactic antimicrobial agents (Andi L. Shane, 2008).

Infectious Diseases in Saudi Arabia

As in the rest of the world, in Saudi Arabia also, the morbidity and mortality from infectious diseases are high. An infection would have its course and severity varied depending on the virulence of the agent and the resistance of the host. Besides, a number of environmental factors also need to be considered. Two of the most common infections and serious health problems in the Western populations have been community-acquired pneumonia and fever of unknown origin (PUO). In the US, each year more than 1.3 million people get hospitalized from infectious diseases. The WHO has attributed Tuberculosis the most common cause of death in the world adult population. Certain factors may increase the risk for TB including HIV status, lower socioeconomic background, poor sanitation, etc. The other common infectious diseases throughout the world were hepatitis B, malaria and meningitis. Alghamdi found that the prior knowledge of prevalence and pattern of infectious diseases in the Western Saudi Arabian population was rather unknown and hence conducted this study to determine the most common infection in the hospitalized and determine their mean time of stay. More than 495 patients that were hospitalized between Jan 2000 to December 2004 at the King Abdulaziz University

Hospital (KAUH) was studied. All data was collected from the patient's medical records. About 8.8 % of the population who were admitted to the hospital or 1 in 11 were admitted for infectious diseases, and slightly more than 50% were males and 54% were native Saudis. Individuals between 26 to 45 years were commonly affected with infectious diseases, followed by the 13-25 year old group. The senior citizen population was least often affected with infectious disease. The most common infectious disease was pneumonia, followed by fever of unknown origin, TB, and viral hepatitis. In women, pneumonia was more common than men, whereas TB and meningitis were more common in men. The other common infectious in the population included bronchopneumonia, malaria and urinary tract infections (Aisha A. Alghamdi, 2009).

The incidence of meningococcal meningitis is common in Hajj pilgrims and in the year 2000, several cases were reported in the Hajj pilgrims. The two common serogroups were serogroups A (24%) and W-135 (37%). The epidemiologists found that the Hajj Pilgrim 2000 Meningococcal attack was in fact two concurrent outbreaks. The W-135 serogroup is endemic in Saudi Arabia. The fatalities were high amongst the pilgrims and hence since the year 1987, mandatory vaccination was being introduced. The vaccine used in fact is quadrivalent in nature (Jairam R. Lingappa, 2003).

The Tuberculosis statistics in Saudi Arabia were also alarming. In a study conducted by Sahal A. M. Al-Hajoj, 2006, it was found from about 1500 cases of Tuberculosis infection, that male-female ratio was 1.27 and 47% of the population being adults between the age groups of 21-40 years. The single drug resistant cases were about 19.7 % and the multi-drug resistant cases were about 47% (Sahal A. M. Al-Hajoj, 2006).

Sahal A. M. Al-Hajoj (2009) conducted another study to find if the mortality and morbidity from tuberculosis could be decreased in Saudi Arabia. There was a rise in the number of cases of TB between 1990 and 2004 by about 6.2%. In Western Saudi Arabia, there is a huge influx of individuals from developing countries who may already be infected with Tuberculosis. The rise in tuberculosis cases may not only be due a rise in infection rate, but also due to better diagnosis techniques. Better TB programs and effective diagnostic laboratories are the need of the hour in controlling cases of tuberculosis in Saudi Arabia. There should also be greater uniformity across the country in standardization.

In the year 2000, there was an epidemic of Rift Valley Fever in Saudi Arabia which had spread from the neighboring North African Region. About 886 patients were included in the study by Tariq A. Madan. The age group affected was the 40 to 50 year, and the male to female ratio was 4:1. The common symptoms recorded included fever, nausea, vomiting, abdominal pain, jaundice, diarrhea, neurological complications, bleeding, visual loss, liver function test abnormalities, leucopenia, renal failure, anemia, etc. There were about 14% mortalities from the disease and were often associated with bleeding, neurological symptoms and jaundice. People with leucopenia had a lower mortality than those who had a rise in the leukocyte count (Tariq A. Madan, 2000).

In the year 2007, the first outbreak of H5N1 occurred in Saudi Arabia and affected 19 poultry farms. Several diagnostic tests were conducted to confirm the infection including Rapid antigen-capture test and real-time RT-PCR. Once the infection was identified in a particular town in Saudi Arabia, the government immediately made a decision destroy the H5N1 affected fleet and the non-affected birds in a radius of 5 kilometers and ensure quarantine measures were followed in the region so that the infection could be prevented from spreading to other regions. Besides, other measures were being adopted including closing bird markets, greater surveillance, quarantine, etc. Within a period of three months from the first detected cases, the epidemic was totally under control. Further within a period of three months (April 2008), Saudi Arabia was declared as H5N1-free (Huaguang Lu, 2009).

In a study conducted by Abdulrahman A. Alrajhi (2004), the mode of transmission of HIV-1 was being studied. It was found that 46% were heterosexual transmission, 26% due to infected blood transfusion, 12% vertical transmission, 5% from homosexual activities and 2% due to use of contaminated syringes during IV drug usage. Most of the heterosexual men got infected from commercial sex workers, and about 65 women got infected from their husbands. In Saudi, the most rampant form of transmission of HIV-1 is heterosexual mode. The mean age of diagnosis of HIV in the 410 individuals who took part in the study was 27.8 years. The adult infection rate is about 0.01%. Women tend to get the infection from their spouses. The rate of infection was relative lower in homosexual men and IV Drug users (Abdulrahman A. Alrajhi, 2004).

Thus it can be seen that infectious diseases are a serious problems. Some of the infections that are common in Saudi Arabia include pneumonia, Fever of unknown origin, tuberculosis, meningitis, HIV, acute viral hepatitis, chronic viral hepatitis, malaria, etc. Besides, outbreaks of several emerging infections are becoming commoner in Saudi. These include the Rift Valley Fever of 2000, H5N1 outbreak of 2007, dengue fever, viral hemorrhagic fever, multi-drug resistant tuberculosis, etc. Many of the zoonotic infectious are getting transmitted to man by vectors such as ticks and mosquitoes (Tariq A. Madani, 2004). The mechanism of development and the transmission of such infections need to be studied.