Person-to-Person Microbial Diseases

1. Chapter 26 Person-to-Person Microbial Diseases

2. Airborne Pathogens Air is not a suitable medium for growth of microorganisms; organisms found in the air are derived from the soil, water, plants, animals, people, etc. Some species can survive travel by air, ex. species found in the upper respiratory tract, even pathogenic species of Staphylococcus and Streptococcus. Avg. human breathes ~500 million liters of air in a lifetime, much of it containing microorganism-laden dust, which can cause respiratory infections. Respiratory pathogens include streptcoccal diseases, diphtheria, whooping cough, tuberculosis, meningitis, and viral infections (cold, flu, etc.)

3. Streptococcal Diseases Nonsporulating, aerotolerant or anaerobic, gram+ cocci. Potent human pathogens = S. pyogenes and S. pneumoniae.

4. Streptococcus pyogenes S. pyogenes ? strep throat, although it can exist as normal flora Can also cause tonsilitis, ear infections, etc. ?-hemolytic on BA. Treatable with antibiotics. Some strains can cause scarlet fever due to a phage-encoded exotoxin. Some strains can also cause rheumatic fever ? tissue destruction of organs, joints, etc., causes autoimmune reaction. Diagnosed using rapid antigen detection (Ag) ? surface Ag�s from throat swab extracted and reacted with Ab�s.

5. Streptococcus pneumoniae Encapsulated Causes lung infections that often occur as secondary infections Cells invade lower respiratory tract Has fatality rate of 30% Can also cause other types of infections

6. Corynebacterium ? Diphtheria Causes diphtheria = severe respiratory disease, usually infects children. Previous infection or immunization provides complete resistance to infection. Forms pseudomembrane on throat that can block the passage of air. Diphtheria toxin can cause systemic damage to major organs.

7. Bordetella ? Whooping Cough Bordetella pertussis ? pertussis exotoxin and an endotoxin. Highly infective respiratory disease often occurring in young children. Violent �whooping� cough can last 6 weeks. Diagnosed by culturing or fluorescent Ab test. Vaccination available to children at specific intervals, and not completely effective.

8. Mycobacterium ? Tuberculosis Acid-fast bacillus transmitted by respiratory route. Results in primary and post-primary infection. Causes delayed type hypersensitivity resulting in the formation of tubercles (aggregates of activated macrophages) visible in the lungs by chest x-ray after chronic infection. Tested for by tuberculin test: protein fraction from the organism is injected under the skin and elicits a localized immune reaction in + individuals within 3 days. Treatment lasts for 9 months.

9. Mycobacterium leprae ? leprosy (Hansen�s disease) The only Mycobacterium species that has not been grown on artificial media. Forms bulblike lesions on the skin, which contain up to 109 bacterial cells/gram of tissue. Lesions can be disfiguring and cause neural damage. Treatment lasts for 1 yr.

10. Mycobacterium bovis Pathogenic in humans and animals. Enters humans via intestinal tract from raw milk. Causes symptoms similar to tuberculosis. Pasteurization of milk and eradication of diseases cattle have eliminated transmission of the disease from cattle to humans.

11. Neisseria meningitidis ? meningitis Meningitis = inflammation of meninges = membranes lining the CNS. = normal flora for up to 30% of individuals. Affects populations in close quarters, ex. military, college dorms. Cultured on Modified Thayer-Martin medium. Causes rapid onset of life-threatening symptoms. Immunization is available. Staphylococcus, Streptococcus, or Haemophilus influenzae also cause meningitis.

12. Viruses ? Respiratory Infections Viral infections = more difficult to treat, treatments often harm host as well. Most viral infections are acute and self-limiting, but some are more serious, ex. smallpox, rabies, measles, mumps, rubella, chickenpox ? all are transmitted by respiratory route and vaccines are available.

13. Measles, Mumps, Rubella, Chickenpox Measles is caused by paramyxovirus ? characteristic rash + other symptoms. Can cause neurological disorders. Mumps is caused by another paramyxovirus. Can cause encephalitis and sterility. Rubella (German measles) is caused by ssRNA togavirus. Symptoms similar to measles, but milder. Can infect fetus of infected mother, causing serious abnormalities. Chickenpox and shingles are caused by varicella virus. Highly contagious, can cause disfiguring marks, remains dormant in nerve cells for years and can erupt later as painful shingles.

14. Colds Colds and flu = most common infectious diseases. Estimates suggest that each person averages more than 3 colds per year over a lifetime! Colds are caused by ssRNA rhinovirus. Symptoms: rhinitis (inflammation of nasal region), nasal obstruction, watery nasal discharges, general malaise, usually without fever ? treat with antihistamine, decongestant, and pain reliever.

15. Influenza Flu is caused by ssRNA influenza virus. Undergoes reassortment of genes called antigen shift and antigenic drift due to mutations. Symptoms: low-grade fever for 3-7 days, chills, fatigue, headache and body aches. Flu vaccines are a combination of antigens from strains that are predicted to predominant during a given flu season. Can result in secondary bacterial infections. Treatment with antiviral agents is available at the beginning of the infection.

16. Staphylococcus Can exist as normal flora and can cause life-threatening disease. Cause common infections of skin and wounds. Gram-pos. cocci. 2 potential pathogens: S. aureus and S. epidermidis, which can inhabit the skin and upper respiratory tract. Transmitted by direct contact. Many diseases are suppurative = pus-forming. Can produce hemolysins, coagulase, leukocidin. Strains of S. aureus can cause TSS (what�s this?) due to exotoxin production. S. epidermidis can cause food poisoning. Staphylococci often cause nosocomial infections (what are these?), including drug-resistant infections.

17. Helicobacter pylori ? Gastric Ulcers Gram-neg., motile, able to withstand pH 2 of stomach, causing ulcers. Mode of transmission not established but suspected to occur through direct contact or contaminated food/water. Ab�s do not protect or prevent colonization. Usually results in chronic infection, but can be treated with antibiotics (long-term treatment is required).

18. Hepatitis Viruses Hepatitis = liver inflammation causes by infectious agent ? destruction of liver = cirrhosis ? liver cancer. Symptoms = fever, jaundice, liver enlargement, abnormal levels of liver enzymes, cirrhosis. Hepatitis A virus: transmitted person-to-person or through contaminated food/water, vaccine available. Hepatitis B virus: transmitted by parenteral route (what�s this?), vaccine available. Hepatitis C virus: also transmitted parenterally, up to 85% of individuals develop chronic hepatitis. There is also a Hepatitis D, E, and G.

19. Gonorrhea STD, caused by Neisseria gonorrhoeae. Gram-neg. diplococcus, sensitive to drying, and transmitted only by person-to-person contact. Symptoms can vary in males and females and may be so mild that they are mistaken for other types of infections. Causes eye infections in newborns, so all newborns are treated prophylactically. Can be treated with antibiotics, though many strains resistant to penicillin. Incidence remains high because: 1. Acquired immunity does not exist, so repeated infection is possible, 2. Oral contraceptives causes females to be more easily colonized, 3. Symptoms in female can be so mild that they are unrecognizable.

20. Syphilis Caused by a spirochete, Treponema pallidum, which is very sensitive to drying and can be viewed by darkfield microscopy. Can be passed from mother to fetus, causing congenital syphilis. Primary lesion = chancre, formed within 2 weeks to 2 months. Disease can enter secondary and even tertiary stages ? fatal infections of cardivascular system or CNS. Penicillin = effective treatment.

21. Chlamydia Caused by Chlamydia trachomatis ? most prevalent cause of venereal disease. Can be transmitted to newborn from infected mother. Causes PID in females ? can cause infertility.

22. Herpes Caused by herpes simplex viruses, which cause painful blisters: HSV-1 ? infects epithelial cells of mouth and lips ? cold sores and fever blisters. HIV-2 ? associated with genital region ? incurable, can cause cervical cancer, blisters may be controlled by acyclovir.

23. Trichomoniasis Caused by protozoan Trichomonas vaginalis. Transmitted by primarily by sexual contact, but can also be transmitted by contaminated toilet seats, sauna benches, and paper towels. Infects males (asymptomatic) and females (vaginal discharge, vaginitis, painful urination). Up to 50% of sexually active females infected, but only ~5% of males are infected. Treatable by antiprotozoal drug.

24. HIV ? AIDS Recognized in 1981. Since then 800,000+ cases reported in U.S. and 400,000 deaths. Worldwide: 50 million infected, 16 million have died. 2 types: HIV-1 (99%+ of cases) and HIV-2 (West African strain). Caused by human immunodeficiency virus = retrovirus (ssRNA). Definition of AIDS: 1. CD4 T cell # less than 200 /mm3 (normal is 600 min.) or less than 14% of all lymphocytes, or 2. Have any one of a # of secondary infections characteristic of AIDS patients, ex. Kaposi�s sarcoma, Pneumoncystis carinii pneumonia � most common, etc.

25. HIV/AIDS (cont.) Cell Interactions: HIV infects cells with CD4 surface protein, which can include B cells, certain brain and intestinal cells, but most commonly macrophages and T helper cells. HIV also needs CCR5 receptor to cause infection and AIDS; people without this receptor don�t get HIV infection/AIDS (this is extremely rare!). HIV ends up causing the systematic destruction of macrophages and T cells (CD4 = 70% of total), leading to a catastrophic breakdown of immunity. Infection: Following reverse transcription, the viral cDNA integrates into the host chromosomal DNA where it exists as a provirus, remaining latent for long periods. T cells producing HIV no longer divide and eventually die. Eventually all other lymphocyte production is shut down and the immune system is destroyed. AIDS patients die of opportunistic infections.

26. HIV/AIDS (cont.) Treatments: treat HIV-specific proteins: reserve transcriptase inhibitors, protease inhibitors. Diagnosis/Detection: usually detect Ab to HIV, not virus itself to see if someone is HIV + or -. Need 2 tests to confirm initial neg. result since Ab take time to be produced. False pos. results and/or lab mixups have also occurred. Can also detect actual viral load with RT-PCR Immunization: Genetic variability of HIV has hampered the development of an AIDS vaccine. Possible vaccines include subunit vaccines, killed intact HIV, or live attenuated virus.