Selected Diesease in Humans

1. Selected Diesease in Humans • Bacterial Diseases • Viral Diseases • Fungal Diseases • Protozoan Diseases

2. 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

3. 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

4. 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

5. 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

6. 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)

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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.

17. 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)

18. 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

19. 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

20. 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)

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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)

27. 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

28. 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

29. 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)

30. 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.