Selected Diseases - Part 1
I Types of Diseases
II Most Common Infectious Diseases
III Diseases of the Respiratory System - General
IV Staph and Strep
A) Staphylococcus aureus B) Strep Throat
C) Scarlet Fever
D) Flesh Eating Bacteria
E) Streptococcus pneumoniae
V Tuberculosis and mycobacteria
VI Diseases of the Oral Cavity
A Bacterial Diseases of the Oral Cavity 1. The Mouth as an Environment
2. Plaque and Dental Caries
3. Periodontal Disease
B Viral and Fungal Diseases of the Oral Cavity
I Types of Disease
You can classify diseases in several ways.
From the microbiologist’s viewpoint:
Infectious disease = disease due to infectious agents (includes: viruses, bacteria, protozoa, worms and other microscopic parasites, etc)
Non-Infectious disease = all other diseases
From the genetics viewpoint:
Inherited disease = due to mutation passed on from one generation to the next via the reproductive cells (germ-line cells).
Cancer (Neoplastic disease) is also a genetic disease. But the mutations are in the somatic cells of the body and are NOT passed on to the next generation.
A few cancers (about 10%) are due to infection with cancer causing viruses.
Congenital disease = present at birth. Not necessarily inherited. Any condition you are born with is technically congenital.
Other ways of viewing disease:
Immunological disease = due to problems with the immune system.
Over-reaction causes allergies etc
Auto-immune diseases are when the immune system attacks the bodies own proteins.
Immuno-deficiency is when the immune system is defective and fails to respond to infection.
Note that some immuno-deficiencies are inherited and others are due to infection.
Iatrogenic disease = due to medical procedure.
Nosocomial infection is an infection acquired in hospital or by some other medical treatment.
Mental disease = disease that affects mental ability and/or behavior. Many different causes. Sometimes hereditary, sometimes due to stress or other environmental factors, sometimes due to injury and occasionally due to infection.
II Most Common Infectious Diseases
In the world today the three infections responsible for most deaths are AIDS (virus), tuberculosis (bacterium) and malaria (eukaryote). All three are unusual diseases. This is because most of the normal diseases have been brought under control and so the strange and difficult ones are left.
Malaria and tuberculosis are ancient diseases but AIDS is an emerging disease and has only existed for about 50 years. Historically, bubonic plague (black death) caused by the bacterium Yersinia pestis has probably killed the most people.
AIDS is caused by HIV (human immunodeficiency virus) a retrovirus that converts its RNA into a DNA copy and then inserts this into the human chromosome. HIV invades the T cells of the immune system. AIDS patients die of opportunistic infections that get out of control. Most virus diseases are controlled by vaccination. There is no vaccine for HIV because the virus mutates too fast.
Tuberculosis is caused by the bacterium Mycobacterium tuberculosis. This has an unusually resistant envelope layer containing unique lipids. It is difficult to treat. Not only is it resistant to many antibiotics but it grows slowly and buries itself in tissues where antibiotics penetrate slowly.
Malaria is a eukaryotic parasite mostly found in the tropics and spread by mosquitoes. It has a complicated life cycle, invades red blood cells in humans and may also infect the liver where it can hibernate and reappear several years later. It contains strange sub-cellular structures, including one related to the chloroplast of plants.
The top 10 most common reported infectious diseases in the US are:
SOURCE: Centers for Disease Control and Prevention
* Chlamydia, 477,638 cases
* Gonorrhea, 392,848 cases
* AIDS, 71,547 cases
* Salmonellosis, 45,970 cases
* Hepatitis A, 31,582 cases
* Shigellosis, 32,080 cases
* Tuberculosis, 22,860 cases
* Primary and Secondary Syphilis, 16,500 cases
* Lyme disease, 11,700 cases
* Hepatitis B, 10,805 cases
But remember that these are diseases that are serious enough to require official reporting. Colds, flu, staph and strep infections etc are far more frequent overall but rarely fatal.
III Diseases of the Respiratory System - General
Respiratory infections are common &emdash; probably the most common infections. Many different infectious agents are involved. Most infections are mild and last a few days. Some, perhaps most, are due to viruses, but many are bacterial and a few are due to fungus. Infections of the upper respiratory tract are more common than those that penetrate to the lungs (= lower respiratory tract).
Terminology:
Strictly speaking "-itis" means inflammation of, not merely infection of. In practice, both infection and inflammation usually occur together.
Upper Respiratory Tract:
Pharyngitis = inflammation of the pharynx or sore throat
Laryngitis = inflammation of the larynx
Epiglottitis = inflammation of the epiglottis
Sinuisitis, tonsilitis = inflammation of the sinuses or tonsils
Lower Respiratory Tract:
Pneumonia = inflammation of lung tissue, caused by infection. Can be viral, even fungal, but is mostly bacterial. Exact symptoms and treatment depend on the organism involved. The air sacs (alveoli) usually fill with pus or fluid and this leads to respiratory problems. Can affect the lobes of the lungs (lobar pneumonia) or the bronchi (bronchial pneumonia).
Bronchitis = inflammation of the bronchi (the branching tubes carrying air deeper into the lungs).
The classic bacterial infections of the lungs are tuberculosis and pneumonia. Pneumonia is caused by a variety of organisms, most of which can now be treated effectively.
Ear infections are linked to upper respiratory infections because the Eustachian tube connects the pharynx with the middle ear. A variety of bacteria can cause ear infections.
Most of the time, especially if treated, we recover from these infections without permanent harm. But occasionally an infection will be more serious, even life-threatening. Anything that blocks the airways may be hazardous. Sometimes chronic infections cause permanent tissue damage.
Factors that predispose to respiratory infections: smoking, breathing particle-laden air such as coal dust, lint, air pollution etc.
IV Staph and Strep
Talaro, Chapter 18 pages 547-566
Staphylococcus aureus and its relatives and Streptococcus pyogenes and its relatives are very common and cause large numbers of infections. Both are gram positive cocci. Staph are found in clusters and Strep in chains.
Staph infections are mostly on the body surface whereas Strep is famous for strep throat &emdash; a respiratory infection &emdash; see below.
A) Staphylococcus aureus
Pyogenic (pus-eliciting) and produces purulent (pus-filled) lesions called abscesses
Mainly an extra cellular pathogen that invades surface tissues
UNLESS it gets into wounds when it may cause serious internal infections
Causes quite a few nosocomial infections in hospitals
Found in the nose, on the mucous membranes and on the skin of about 30% of the population &emdash; much more common on hospital staff.
Source of infection - your own microflora or from hospital staff
Survives well on inanimate objects (lab coats, gloves, bedding).
Makes several toxins (varies from strain to strain)
Toxic shock syndrome and tampons
Staphylococcus aureus growing on ultra-absorbent tampons. Local infection occurs. Makes toxic shock syndrome toxin-1 (TSST-1). About 15% of Staph aureus make this toxin. Fever, nausea, vomiting, diarrhea, rash, sometimes harms kidneys, liver etc. Occasionally fatal (approx 2%).
Penicillins and MRSA
Most strains of S aureus are resistant to penicillin because of beta-lactamase production. Standard treatment is methicillin and related penicillins (oxacillin, cloxacillin), which are not degraded by S. aureus beta-lactamase.
MRSA = Methicillin resistant Staphylococcus aureus is a major emerging problem. MRSA can be treated with vancomycin. Unless they are also resistant to vancomycin.
B) Strep Throat
The most familiar bacterial infection of the upper respiratory tract is strep throat due to Streptococcus pyogenes, a beta hemolytic organism. Most often seen in children but adults get it too. Very red very sore throat can develops very fast. Although a child with strep throat feels terrible, the main problem with S. pyogenes infections is the potential for rheumatic fever and glomerulonephritis, which can follow the streptococcal infection.
[Beta-hemolytic streptococci have a clear zone around the colonies on blood agar plates due to lysis of the red blood cells. Alpha-hemolytic bacteria have a green color and a partial lysis around the colonies.]
Both complications are due to cross-reacting antibodies that attack the host tissue (heart or kidneys). This is due to surface proteins of the strep being similar to those of the body’s own cells. So antibodies made against the invading strep damage the body’s own tissues. Rheumatic fever damages heart valves and predisposes you to infections and inflammation of the heart - bacterial endocarditis. Individuals with a history of rheumatic fever may receive antibiotics before invasive dental procedures that are likely to produce bacteremia (bacteria in the blood). For most of us transient bacteremia is not a problem, but for someone with a damaged heart valve it could start a serious infection.
Previously, diagnosis was by culturing the organism, but now faster immunological methods are used. Strep antigens are extracted from a throat swab and antibody coated latex particles are mixed with the extract. Takes about 10 minutes.
C) Scarlet Fever
Scarlet fever is due to S. pyogenes that has an extra toxin (erythrogenic toxin) that causes a rash. The toxin gene is carried on a prophage (a bacterial virus that has integrated its DNA into the bacterial chromosome).
Scarlet fever is usually spread person to person nowadays. In earlier times non-pasteurized milk used to be the major vehicle. Scarlet fever can still be spread by contaminated food, usually if someone who is infected is handling the food.
D) Flesh Eating Bacteria
Flesh eating disease = necrotizing fasciitis. It is a rare complication that is due to rare unusually virulent strains of S. pyogenes with extra toxins that have managed to get into cuts on the skin.
Rarely drug resistant and easy to treat if diagnosed early.
E) Streptococcus pneumoniae
The most common bacterial pneumonia is caused by S. pneumoniae. These are alpha-hemolytic strep. From 40% - 70% of adults carry S. pneumoniae but become ill only if the immune system is not functioning well. The fatality rate before antibiotics was 25%-30%, now it is closer to 5% (down to 1% for younger patients treated early). There are over 80 different serological subtypes of S. pneumoniae as determined by the capsule, which is the outer layer and the main target of the immune response. It is possible to get one subtype, recover and then get another.
V Tuberculosis and Mycobacteria
Talaro Chapter19 pages 591-600
Mycobacteria
Mycobacteria are slow growing strict aerobes. Two most serious diseases are tuberculosis (TB) and leprosy. They are acid fast due to their characteristic waxy lipids (mycolic acids) in the cell walls. These give them extra protection. They can survive drying are acid resistant and remain viable for long periods of time, especially in sputum, pus, blood, etc. They are very resistant to phagocytosis and will continue to live inside phagocytes.
Tuberculosis is caused by Mycobacterium tuberculosis, although a few other mycobacteria are occasionally responsible. Tuberculosis is normally transmitted by inhalation of airborne particles. Tuberculosis infects the lungs and causes a severe form of pneumonia that may be eventually fatal if not treated. However, there are many complications and variations of tuberculosis.
Mycobacterium tuberculosis is a long thin rod that tends to associate into masses or strands. No toxins or destructive enzymes.
Mycobacterium bovis is found in cattle and can be transmitted to man. This causes "bovine tuberculosis" which is similar but usually less severe than human tuberculosis due to Mycobacterium tuberculosis. It used to be transmitted by way of contaminated milk but better conditions in dairies and testing of cattle have decreased this dramatically.
Treatment
Use a cocktail of three antibiotics to avoid resistance
Isoniazid plus rifampin plus pyrazinamide is the best modern combination of drugs
Several antibiotics only used against mycobacteria include: Isoniazid (INH = isonicotinic hydrazide), pyrazinamide, ethambutol, thioacetozone, PAS (para-aminosalicylic acid).
Other antibiotics used against mycobacteria as well as normal bacteria: rifampin and streptomycin. Historically streptomycin was most widely used but today rifampin is favored.
Long and tedious 6 to 24 months
Must continue to end or a few bacteria hidden deep in tissue will survive and the infection will start up again
DOT = directly observed therapy = the nurse watches you to make sure you don’t skip the medicine
Vaccination
BCG (Bacillus Calmet-Guerin) is an attenuated strain of tuberculosis used as a vaccine in countries where TB is common. Not especially effective (protects maybe 80% of children but only half or less of adults). Not in use in USA or most other industrial nations where TB is rare.
Occurrence and History
Tuberculosis was extremely common during the 1800s and early 1900s. It was a major health problem in the US until the introduction of streptomycin in the 50's, when the frequency began to decline. From 1985 to 1995 the frequency went up and then down again, however the fatality rate has continued to decline. Tuberculosis is re-emerging in the Third World and the inner cities. It is a particular problem among individuals with AIDS, the homeless and others living in crowded unhygienic conditions in inner cities or Third World nations. About 2-3 million deaths per year, mostly in Third World nations.
Most cases occur among American Indians, Blacks, Asians, and Hispanics, particularly in some immigrant groups. Also in the elderly &emdash; decline of immune system with age. Genetic factors affect susceptibility. Also poor nutrition, unsanitary conditions and crowding. Recently in the US there has been a significant increase in tuberculosis in the 25-44 age group that is associated with AIDS and drug abuse. Tuberculosis has been around for a long while - found in mummies from Egypt and Peru and even in Stone Age burials.
In the 1800s tuberculosis was even considered a fashionable way to die. Mimi the heroine in the opera La Boheme dies of tuberculosis in the last act, so weak she can hardly walk. Nonetheless, she collapses still singing well enough to be heard in the highest balcony. Real people who died of tuberculosis: Frederic Chopin, John Keats, Elizabeth Barrett Browing, Robert Louis Stevenson. Some people even believed tuberculosis would give you exceptional creative powers and genius.
VI Diseases of the Oral Cavity
Talaro Chapter 21 pages 654-659
A Bacterial Diseases of the Oral Cavity
1. The Mouth as an Environment
Our mouth is a small ecosystem, with a number of different ecological niches and an environment that changes. It is inhabited by a large variety of microorganisms. Different ones live in different places.
The ecological niches: tongue, cheeks, palate, teeth and gingival crevices. Even around teeth there are different conditions - the backside is frequently in contact with the tongue, some surfaces are smoother than others. The amount of oxygen available is different in different places so microorganisms range from aerobes to micro-aerophiles to anaerobes.
Saliva constantly coats the surfaces of the mouth, including the teeth. Somewhere about one liter a day of saliva is produced. From time to time food is brought in, providing all the nutrients needed for a wide variety of microorganisms. This includes sugars, which are catabolized to some products of interest.
The microorganisms: how many different kinds depends on who you believe. Estimates range form 300 to 1000 different species. Although this includes a large number of bacteria, there are also viruses, fungi and protozoans present. But we will concentrate on the bacteria.
2. Plaque and Dental Caries
How does plaque form and what happens if it is not removed? Start with an absolutely clean tooth. Immediately it is coated with saliva, which has proteins in it, some of which stick to the tooth. The first bacteria to stick to the protein coating on the tooth are Streptococci [G+ cocci] and Actinomycetes [filamentous]. When sucrose is taken in Streptococcus mutans and to a lesser extent other organisms, produce a gummy polysaccharide. This gives other organisms a place to attach to and holds everything together - salivary proteins, bacteria and their extracellular products. This is dental plaque.
Other bacteria that attach include Lactobacillus [G+ rods], Bacteriodes, Fusobacterium, and Treponema. Several of the species present, mostly streptococci and lactobacilli, will metabolize sugars to lactic acid. If the plaque is not removed the acid will eventually lower the pH within the plaque and when it gets below 5 the Ca PO4 in the enamel will begin to dissolve. The result is a cavity (dental caries). If not treated this lesion will progress to the interior of the tooth and become more serious so that the tooth might be lost.
Vaccines against oral microorganisms? We don't want to kill all our normal flora because then the mouth would open to colonization by all kinds of pathogens. However, a vaccine against Strep mutans might protect against caries.
Things we can do: limit intake of sucrose and other sugars, brush and floss to remove the build-up of plaque before it becomes impossible to remove at home (calculus). See dental hygienist regularly. Public health measures - fluoride in drinking water helps prevent dental caries.
3. Periodontal Disease
Dental caries are a disease of the hard tissues and are most common in children and adolescents. But in older individuals the most common problems are in the soft tissues, which can also become diseased.
Gingivitis - the least serious condition. Plaque, or calculus, including a variety of microorganisms accumulates near the gums and in the gingival crevice between the gums and the tooth. The gums become irritated and inflammation results. The bacteria in the crevice are mostly G- anaerobic rods such as Veillonella, Bacteroides, Fusobacterium, Eikenella, and Eubacterium together with some streptococci and spirochetes.
Symptoms of gingivitis include bleeding of the gums when the teeth are brushed, redness, and swelling. Nearly everybody has some degree of gingivitis at some time.
If gingivitis progresses more serious disease results with more virulent bacteria becoming more prominent. Inflammation spreads and finally the area involved can be great enough to affect the bone.
Acute necrotizing ulcerative gingivitis (ANUG) has been called trench mouth or Vincent's disease. It is characterized by the presence of many anaerobic organisms including Treponema vincentii and an assortment of other spirochetes plus fusobacteria and actinomycetes.
Symptoms: bleeding, enough pain to make chewing difficult. This condition, unlike the others, can be treated with antibiotics. It seems to be associated with stress. The name trench mouth came from it being frequent in wartime in men in battle - a high stress environment where good dental hygiene was not a high priority.
B Viral and Fungal Diseases of the Oral Cavity
1. Mumps - a paramyxovirus. It replicates first in the upper respiratory tract, then is carried by the circulatory system all over, but it mainly infects the parotid glands. So an individual with mumps will have painfully swollen glands for several days to a week.
Mumps is now preventable by vaccine and the incidence in the US has decreased dramatically. Besides the discomfort there are some serious side effects that occasionally occur - encephalitis, infection of eye, ear, testes, ovaries, and other organs. These are more serious in adults than children and can cause sterility in adult males.
The other fairly common viral infection of the mouth is Herpes simplex virus, type 1, causing cold sores.
2. Candida albicans (a yeast type fungus) infection of the mouth is called thrush. Sometimes appears following long-term treatment with antibiotics that has reduced the normal bacterial flora.