Infectious diseases, also known as transmissible diseases or communicable diseases, comprise clinically evident illness (i.e., characteristic medical signs and/or symptoms of disease) resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism. In certain cases, infectious diseases may be asymptomatic for much or even all of their course in a given host. In the latter case, the disease may only be defined as a "disease" (which by definition means an illness) in hosts who secondarily become ill after contact with an asymptomatic carrier. An infection is not synonymous with an infectious disease, as some infections do not cause illness in a host.
Infectious pathogens include some viruses, bacteria, fungi, protozoa, multicellular parasites, and aberrant proteins known as prions. These pathogens are the cause of disease epidemics, in the sense that without the pathogen, no infectious epidemic occurs.
A tooth abscess or root abscess is pus enclosed in the tissues of the jaw bone at the apex of an infected tooth's root(s). Usually the abscess originates from a bacterial infection that has accumulated in the soft, often dead, pulp of the tooth. This can be caused by tooth decay, broken teeth or extensive periodontal disease (or combinations of these factors). A failed root canal treatment may also create a similar abscess.
Examples of types of dental abscess include:
Dental caries, also known as tooth decay or a cavity, is an infection, bacterial in origin, that causes demineralization and destruction of the hard tissues of the teeth (enamel, dentin and cementum). It is a result of the production of acid by bacterial fermentation of food debris accumulated on the tooth surface. If demineralization exceeds saliva and other remineralization factors such as from calcium and fluoridated toothpastes, these once hard tissues progressively break down, producing dental caries (cavities, holes in the teeth). Today, caries remain one of the most common diseases throughout the world. Cariology is the study of dental caries.
Depending on the extent of tooth destruction, various treatments can be used to restore teeth to proper form, function, and aesthetics, but there is no known method to regenerate large amounts of tooth structure. Instead, dental health organizations advocate preventive and prophylactic measures, such as regular oral hygiene and dietary modifications, to avoid dental caries.
Anaerobic infections are caused by anaerobic bacteria. Anaerobic bacteria do not grow on solid media in room air (0.04% carbon dioxide and 21% oxygen); facultative anaerobic bacteria can grow in the presence as well as in the absence of air. Microaerophilic bacteria do not grow at all aerobically or grow poorly, but grow better under 10% carbon dioxide or anaerobically. Anaerobic bacteria can be divided into strict anaerobes that can not grow in the presence of more than 0.5% oxygen and moderate anaerobic bacteria that are able of growing between 2 to 8% oxygen. Anaerobic bacteria usually do not possess catalase, but some can generate superoxide dismutase which protects them from oxygen.
The clinically important anaerobes in decreasing frequency are: 1. Six genera of Gram-negative rods (Bacteroides, Prevotella, Porphyromonas, Fusobacterium, Bilophila and Sutterella spp.); 2. Gram-positive cocci (primarily Peptostreptococcus spp.); 3. Gram-positive spore-forming (Clostridium spp.) and nonspore-forming bacilli (Actinomyces, Propionibacterium, Eubacterium, Lactobacillus and Biﬁdobacterium spp.); and 4. Gram-negative cocci (mainly Veillonella spp.) .
Lung abscess is necrosis of the pulmonary tissue and formation of cavities (more than 2 cm) containing necrotic debris or fluid caused by microbial infection.
This pus-filled cavity is often caused by aspiration, which may occur during altered consciousness. Alcoholism is the most common condition predisposing to lung abscesses.