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Selected Diesease in Humans. Bacterial Diseases Viral Diseases Fungal Diseases Protozoan Diseases. Bacterial Diseases. Pathogenic bacteria typically enter through a specific portal of entry and begin as a localized infection; some bacteria have more than one portal

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Selected Diesease in Humans

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Selected diesease in humans l.jpg

Selected Diesease in Humans

  • Bacterial Diseases

  • Viral Diseases

  • Fungal Diseases

  • Protozoan Diseases


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Bacterial Diseases

  • Pathogenic bacteria typically enter through a specific portal of entry and begin as a localized infection; some bacteria have more than one portal

  • Many bacterial pathogens can spread from the initial site to other areas of the body

  • Many bacterial infections have been effectively treated with antibiotics; evolution of drug resistance in some strains have made them difficult to treat

  • Several important pathogens are curtailed through the use of vaccines


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Bacterial Diseases

  • Selected airborne bacterial pathogens

    • Streptococcus pyogenes

      • Gram + cocci, Lancefield serological group “A”, catalase negative, beta hemolytic

      • Associated with streptococcal pharyngitis, scarlet fever (with erythrogenic toxin-producing strains), systemic infections, immune-related complications such as rheumatic fever and glomerulonephritis, and a skin infection called erysipelas


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Bacterial Diseases

  • Selected airborne bacterial pathogens

    • Neisseria meningitidis

      • Gram negative diplococcus; fastidious; cultured on chocolate agar

      • Highly contagious

      • Generally begins as an upper respiratory tract infection; may spread into bloodstream and then to the meninges

      • Symptoms of meningitis: “stiff neck,” headache, dizziness, disorientation, seizures, coma, death


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Bacterial Diseases

  • Selected airborne bacterial pathogens

    • Mycobacterium tuberculosis

      • Acid-fast rods, grows very slowly in culture

      • Detected by acid-fast stains of sputum, lung x-ray, culture

      • Tuberculin skin test determines if someone has been exposed to M. tuberculosis, but doesn’t necessarily mean the person has tuberculosis

      • Symptoms: Cough; destruction of lung tissue; tubercle formation in lungs; spread to other areas of the body with tissue damage


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Bacterial Diseases

  • Selected airborne bacterial pathogens

    • Legionella pneumophila

      • Gram negative aerobic rods; natural habitat is highly aerated aquatic environments such as streams

      • May contaminate bulding ventilation systems, water faucets, or other moist surface and is transmitted to humans who come into aerosols created from these sources

      • Symptoms: Mild to severe pneumonia (lung infection with fluid buildup in the lungs)


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Bacterial Diseases

  • Selected foodborne bacterial pathogens

    • Clostridium botulinum

      • Gram + anaerobic rods; forms spores; found in soil

      • Can contaminate raw or underprocessed foods; toxin forms in food before it is consumed, so it is a foodborne intoxication

      • Secretes botulinum toxin, a deadly neurotoxin that blocks nerve impulses at motor neuron end plate synapses and causes flaccid paralysis

      • Symptoms begin as soon as the toxin begins to be absorbed in the stomach

      • Death is due to respiratory and cardiac failure


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Bacterial Diseases

  • Selected foodborne bacterial pathogens

    • Staphylococcus aureus food poisoning

      • Gram + cocci; catalase and coagulase positive; common skin flora

      • Some strains of Staph. Aureus produce an enterotoxin that can be secreted in contaminated food; toxin forms in food before it is consumed, so it is a foodborne intoxication

      • The toxin causes mild to moderate cramping and diarrhea; symptoms appear a few hours after consuming the food and usually last only a few hours


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Bacterial Diseases

  • Selected foodborne bacterial pathogens

    • Salmonella species

      • Gram negative rods; facultatively anaerobic; a member of Enterobacteriaceae

      • Transmitted in contaminated foods, especially meat, poultry, & dairy products

      • A foodborne infection: Bacteria must colonize the intestinal tract to cause symptoms

      • Cramping, nausea, diarrhea

      • Salmonella typhi causes typhoid fever: intestinal ulceration, invasiveness, rose-colored rash on abdomen, less diarrhea but very high fever


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Bacterial Diseases

  • Selected foodborne bacterial pathogens

    • Helicobacter pylori

      • Gram negative microaerophilic spirillum

      • Groes underneath the mucous layer in the stomach

      • A major cause of stomach ulcers


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Bacterial Diseases

  • Selected soilborne bacterial pathogens

    • Bacillus anthracis

      • Gram + facultatively anaerobic rods; forms spores

      • Found in contaminated soil or animals (livestock)

      • May either be transmitted through skin contact (cutaneous anthrax), oral ingestion (intestinal anthrax), or inhalation (pulmonary anthrax)

      • Lesions & tissue destruction occur at the affected sites

      • Pulmonary anthrax has close to a 100% fatality rate


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Bacterial Diseases

  • Selected soilborne bacterial pathogens

    • Clostridium tetani

      • Gram + anaerobic rods; forms spores; found in soil

      • May grow in contaminated wounds or cuts, where it produces the toxin tetanospasmin; a neurotoxin that acts as a cholinesterase inhibitor; mainly effects the central nervous system

      • Nerve synapses remain closed because cholinesterase fails to break down the neurotransmitter acetylcholine; this causes rigid paralysis


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Bacterial Diseases

  • Selected arthropodborne bacterial pathogens

    • Borrelia burgdorferi

      • Gram negative spirochaete; causative agent of Lyme disease

      • Transmitted through the bite of an infected deer tick (Ixodes)

      • Initial symptoms include fever, congestion, lymph node swelling, “flu-like” symptoms and the developemnt of a large, spreading rash (erythyma chronicum migrans) at the site of the tick bite

      • If untreated, inflammation & damage to joints, arthitis-like symptoms, and damage to the cardiovasular system can result


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Bacterial Diseases

  • Selected arthropodborne bacterial pathogens

    • Rickettsia rickettsiae

      • Gram negative rickettsia; a small, irregularly-shaped bacterium that is an obligately intracellular parasite

      • Causative agent of Rocky Mountain Spotted Fever

      • Transmitted through tick bites

      • Symptoms include high fever, a rash that begins as pinpoint spots at the extremities and spreads to the trunk of the body (macropapipular rash), seizures and coma


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Bacterial Diseases

  • Selected arthropodborne bacterial pathogens

    • Rickettsia prowasekii

      • Gram negative rickettsia; a small, irregularly-shaped bacterium that is an obligately intracellular parasite

      • Causative agent of epidemic typhus

      • Transmitted through human lice; predominately spread via body lice, not head lice or crab lice

      • Symptoms include high fever, a rash that begins as pinpoint spots on the trunk of the body and spreads to the extremities (macropapipular rash), seizures and coma; has a very high fatality rate

      • Easily spread under conditions of reduced sanitation where lice are likely to spread


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Bacterial Diseases

  • Selected bacterial STDs

    • Treponema pallidum

      • Gram negative spirochaete; transmitted via sexual contact or congenitally

      • Initial symptom (primary syphilis) is usually the appearance of a crusted, purple, painless lesion called a hard chancre at the site of infection; lesion usually disappears on its own after a few weeks but the infection remains in the blood

      • Later symptoms include fever, rash, & flu-like symptoms (secondary syphilis) and the formation of lesions called gummae throughout the body (tertiary syphilis), with neurological, cardiovascular, & other damage.


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Bacterial Diseases

  • Selected bacterial STDs

    • Neisseria gonorrhoeae

      • Gram negative diplococcus; fastidious; cultured on chocolate agar

      • Transmitted via sexual contact or congenitally

      • Urinary tract symptoms: Urethritis with painful urination & pus discharge; cystitis; kidney infection

      • Male reproductive symptoms: Prostatitis; epididymitis

      • Female reproductive symptoms: Infections of the vagina, cervix, uterus, Fallopian tubes; pelvic inflammatory disease

      • Eye infections (trachoma)


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Bacterial Diseases

  • Selected miscellaneous bacterial infections

    • Pseudomonas aeruginosa

      • Gram negative aerobic rod; commonly found in soil or aquatic environments

      • Can contaminate aerated moist surfaces such as faucets, respiratory equipment, etc.

      • A common cause of hospital-acquired (nosocomial) infections

      • Respiratory tract infections, urinary tract infections, and severe infections in burn patients


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Bacterial Diseases

  • Selected miscellaneous bacterial infections

    • Staphylococcus aureus infections

      • Gram + cocci; catalase and coagulase positive; common skin flora

      • Infections associated with Staph. aureus include pimples, boils, abscesses, carbuncles, septicemia, scalded skin syndrome in infants, toxic shock syndrome


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Viral Diseases

  • Viruses are classified based on

    • nucleic acid structure (DNA or RNA; single- or double-stranded; segmented or nonsegmented)

    • capsid structure (helical, icosahedral, or complex)

    • envelope structure (enveloped or nonenveloped)

    • host (animal, plant, or bacteria)

    • mechanism of replication

    • site of infection (pneumotrophic, dermatotrophic, viscerotrophic, neurotrophic)


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Viral Diseases

  • Influenza

    • Member of Orthomyxovirus family

    • Segmented (8 segments), single-stranded, negative-sense RNA that encode 11 proteins

    • RNA is packaged into helical nucleocapsids and surrounded by an envelope

    • Two envelope proteins: hemagluttinin (H) and neuraminidase (N)

    • Three major types: Influenza A, Influenza B, & Influenza C; of which Influenza A strains are the most virulent in humans


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Viral Diseases

  • Influenza

    • Influenza can be transmitted via human-human airborne contact, or from contact with contaminated birds, swine, or other animals

    • Symptoms

      • in mild cases include fever, lymph node swelling, congestion, fatigue, primary & secondary pneumonia

      • Highly virulent strains may exhibit hemorrhaging from nose & mouth, ears, eyes, intestine, internal organs

      • Other complications include Guillian-Barre & Reyes syndrome

    • Antigenic variation and genetic recombination in the H & N proteins can lead to new strains of influenza

    • Each year epidemiologists determine the best “combination” vaccine for the year’s prevalent strains


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Viral Diseases

  • Influenza

    • Some important pandemics of influenza

      • H1N1: 1918-1920 “Spanish flu;” estimates of deaths worldwide range from 30 - 100 million people

      • H2N2: 1957-1958 “Asian flu” with 1 - 1.5 million deaths

      • H3N1: 1968-1969 “Hong Kong flu” with about 1 million deaths

      • H5N1: Current “avian flu” threat

        • Genotype first observed in 1959, but evolved into the current highly pathological strain that was discovered in 2004

        • No human to human transmission seen yet; cases have been bird to human contact

        • If human to human transmission were to evolve in this strain, experts have estimated that perhaps 5 - 150 million people could die worldwide


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Fungal Diseases

  • Properties of Fungi

    • Eukaryotic

    • Fungal cell walls with cellulose & usually with chitin

    • Heterotrophic metabolisms

    • Many are saprophytes; a few species are parasitic

    • Morphology: single cells (yeasts) or filaments (hyphae)

    • Most species have both sexual & asexual mechanisms of reproduction


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Fungal Diseases

  • Candida albicans

    • Grows as a yeast or sometimes as short hyphae (pseudohyphae)

    • Common normal flora in the mouth, intestine, & vaginal tract

    • Competiton with bacterial flora helps keep Candida in check; conditions that reduce bacterial flora (e.g. antibiotic use) or weaken immune system (e.g. AIDS) can cause candidiasis infection to develop

    • Symptoms include oral candidiasis (thrush), intestinal candidiasis, and vaginal candidiasis


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Fungal Diseases

  • Dermatophytic fungal infections

    • Infections of the hair, skin, nails

    • Several genera of dernmatophytic fungi: Microsporum, Epidermophyton, Trichophyton

    • Symptoms: Scaly, red or raised rash on skin (“ringworm”), discolored and splitting nails, hair loss

    • Often described by the term “tinea” with the name of the area infected: tinea corporis (ringworm of the body); tinea pedis (“athlete’s foot”); tinea unguium (ringworm of the nails); tinea cruris (“jock itch”); tinea barbae (ringworm of the beard)


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Protozoan Diseases

  • Properties of Protozoa

    • A heterogeneous group of eukaryotic microbes

    • Generally characterized by lack of a cell wall and a heterotrophic metabolism (although one group, Euglena, is photosynthetic

    • Most are free-living; a few are parasitic

    • Classical classification based on mechanism of motility; rRNA data has shown the existance of more phyla than previously suspected

    • Motile by pseudopodia, flagella, cilia, or nonmotile

    • Most reproduce asexually; a few groups have complex sexual & asexual cycles


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Protozoan Diseases

  • Giardia lamblia

    • A flagellated parasite of humans and other mammals

    • Actively growing and reproducing form(trophozoite) grows in the intestinal tract of the host

    • In the intestine, trophozoites develop into cysts that are shed in the feces; the disease is transmitted when the next host ingests contaminated food or water and the cysts break open and develop into new trophozoites in the intestine

    • Symptoms: Profuse, foul-smelling diarrhea; dehydration; chronic recurrences

    • Often misdiagnosed; diagnosis requires microscopic or serological ID of trophozoites & cysts in stool or intestinal contents


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Protozoan Diseases

  • Toxoplasma gondii

    • Member of the phylum Apicomplexa, a group characterized as parasites with complex lifestyles having both sexual and asexual stages

    • The sexual stage develops only in members of the cat family, with sexual cysts (oocysts) shed in the feces

    • Oocysts are ingested by other animals (e.g. mice, cattle), where they travel to the muscle tissue & develop into asexual cysts (tissue cysts)

    • Cats acquire the parasite by ingesting the infected meat of prey such as mice

    • Humans acquire the parasite via the oral route, through contact with cat feces or ingestion of contaminated meat (often beef)


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Protozoan Diseases

  • Toxoplasma gondii (cont)

    • Infections in humans are often asymptomatic, except when the person is immunocommpromised, in which case encephalitis may develop

    • Pregnant women are at risk because the parasite can cross the placental barrier & infect the baby, with the possibility of birth defects or miscarriage

    • The parasite is very prevalent in humans, with estimates of 65% of people worldwide and 33% of people in the US over 12

    • Studies in mice suggest the parasite may actually alter its host’s behavior; e.g., mice exhibit riskier behavior such as less fear of cats. Some studies have suggested effects of the parasite on human behavior as well.


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