Chapter 14

1. Chapter 14 Principles of Diseases and Epidemiology

2. Terms and definitions • Pathology: the study of diseases of (1) how diseases occur (etiology), (2) how diseases develop (pathogenesis), (3) and the outcome of a specific disease. • The processes: Exposed, (arrival of the pathogen), infected (colonization of the pathogen) and disease (decrease in the host’s state of health).

3. Not every creature is a killer: The normal flora • Many microbes forms symbionts in various parts of our body. They are usually harmless. Some of them stay permanently, others are transients.These organisms are important because they are antagonistic to those real pathogens. • Most of the normal flora microbes benefited by our body and they don’t caused harm (commensalism), others do return some benefits (mutualism) to the host.

4. The diseases-causing bugs Most of them are parasites offering no helps to the host. The opportunistic pathogens are normal habitat of our body. They rebel when the body’s condition changes or when they get into the wrong place of our body.

5. The cause of disease: Etiology Kock’s postulates: • Same pathogen is found in all the diseased hosts. • The pathogen can be grown in pure culture • The cultured pathogen causes disease in healthy tested animals. • The pathogen can be isolated from the diseased tested animals.

6. Exceptions • Sometimes pathogens cannot be cultured. • Sometimes pathogens indirectly cause the disease. • Mixed infection can occur. • Helper strains are needed.

7. Description of diseases • Symptoms are non-quantifiable feeling described by the patient.(patients’s feeling.) • Signs are quantifiable descriptions of a disease. (Doctor’s observation.) • Syndromes: A group of symptoms and signs that collectively indicate or characterize a disease, a psychological disorder, or another abnormal condition.

8. Occurrences of disease • Sporadic disease: occurs periodically but occasionally. • Endemic disease: occurs consistently within a certain population/place. • Epidemic disease: can spread from places to places. • Pandemic disease: disease spread worldwide.

9. Duration of disease • Acute disease onset rapidly. • Chronic disease develops slowly. • Subacute disease develops in weeks. • Latent disease develops after a prolong period.

10. Development of disease • Local infection: the infective agent did not migrate to other parts of the body. • Systemic (generalized infection): the infection agents spread thought out the body. Systemic infection is typified by the presence of foreign substances in the blood (bacteremia /viremia/ toxemia.) Septicemia is a serious problem when pathogens start growing in the blood.

11. Development of Disease (cont) • Primary infection is the infection that causes the initial illness. • Secondary infection is one cause by opportunistic pathogen after the host was damaged by the initial illness.

12. Factors affecting the onset of disease Predisposing factors (include physical and chemicals factors) such as • Age • Gender • Location • Climate and weather • Nutrition

13. Development of Disease • Incubation period • Prodromal period • Period of illness • Period of decline • Period of Convalescence

14. Spread of disease • Communicable diseases can spread form one host to the other. • Some pathogens are especially easy to transmitted to the others. They are called contagious disease. • Noncommunicable diseases cannot transmitted to other host.

15. Infection Reservoirs Carriers as human reservoirs: A story about a woman we called her Typhoid Mary. The sad story of Mary Mallon is also about a world of strict class divisions and prejudice against immigrants and women. She was an Irish immigrant cook. Between 1900 and 1907, she infected twenty-two New Yorkers with typhoid fever through her puddings and cakes; one of them died. Tracked down through epidemiological detective work, she was finally apprehended as she hid behind a barricade of trashcans. To protect the public's health, authorities isolated her on Manhattan's North Brother Island, where she died some thirty years later. Strangely, other male typhoid carriers were let go in a few days.

16. Some occasional thoughts To what degree are we willing to sacrifice our individual liberty to protect the society? How far should we go in the age of AIDS, drug-resistant tuberculosis to accept the side effects of massive immunization? For anyone who is concerned about the threats and quandaries posed by new epidemics, Typhoid Mary is a vivid reminder of the human side of disease and disease control.

17. Animal Reservoirs Zoonosis is a disease of animals, such as rabies or psittacosis, that can be transmitted to human beings.

18. Nonliving Reservoirs Contaminated soils and waters

19. Disease transmission • Contact transmission. • Direct contact through physical contact such as kissing, sexually transmitted, etc. • Indirect contact through inanimate object (fomite). • Airborne and droplet.

20. Vehicle Transmission • By air, by food, and by water. • By vectors such as arthropod. mechanical transmission- the legs of the fly, vector does not directly involved. Biological transmission:vector was part of the life cycle of the pathogen.

21. Portal of Exit -Knowing the routs of pathogens getting out of the body is very important to control diseases. Respiratory and gastrointestinal tract. Urogenital tract. Cuts and wound. Blood, needles and syringes.

22. Nosocomial diseases Disease acquired during hospital stay. The hospital environment select the resistant bacteria. The people are usually compromised, The chain of transmission from person to person, from person to fomite, is easy, if unchecked.

23. Control and Prevention of Nosocomial infections • Monitor aseptic techniques and handling contaminated materials. • Established a active infection control committee that involved the epidemiologists, physicians, nurses, and the cleaning staffs to review daily reports.

24. Emerging diseases Reasons for increase EID; • New diagnostic techniques recognize previously unknown illness. • Rare diseases became common. • Increase in life span of human population. • Resistance. • New infectious rout of pathogens.

25. Bacterial EID examples Lyme Disease. First identified in 1975; now the most common vector-borne disease in the U.S. • Caused by the spirochete Borellia bergdorferi.in the deer ticks. • A vaccine is now available for persons at high risk of exposure; Clinical Features: Similar to syphilis and has three distinct stages: • Stage 1 : Erythema migraine (EM) at site of tick bite. • Stage 2 (Within days or weeks of Stage 1): Secondary annular skin lesions. Fever, chills, arthralgias, myalgias, stiffness, palpitations, headache, extreme fatigue. • Stage 3 : Acrodermatitis chronica, primarily lower arms and legs. Subtle encephalopathy (memory and mood disturbance) and/or polyneuropathy, recurrent relatively brief attacks of acute poly- or oligoarticular arthritis involving large joints, most often knees. • Diagnostic Testing: Serum: ELISA.

26. Plague Key Facts: Increasing incidence in 13 western states; Transmission to humans occurs through the bite of an infected rodent flea, contact with the blood or tissues of an infected rodent, or by inhalation of organisms aerosolized by an infected rodent or human. Incubation period is 1-3 days Mortality rates are 50-60% for untreated bubonic and 100% for untreated pneumonic plague; early antibiotic treatment is effective. Clinical Features: Three forms: bubonic, septicemic, and pneumonic; Signs and symptoms tend to be mild at first. Enlarged, tender lymph nodes; often absent in septicemic and pneumonic forms Skin mottling (esp. chest, abdomen, face); Fever is not universal; WBC may be elevated or depressed Rapid development of septic shock. Diagnostic Testing: Gram stain; fluorescent antibody (FA); and culture on blood agar; Treatment: Antibiotics are effective if started early enough. Effective agents include.

27. Human Ehrlichiosis Key Facts: First case worldwide 1954 in Japan; First documented U.S. case in 1986 in Arkansas; Highest reported incidence is in men 60-69 years old; occurs at all ages/ both genders; Responsible organism is Ehrlichia chaffeensis (after Fort Chaffee, Arkansas), an obligate intracellular cocco-bacillus resembling rickettsia. Populations at Risk: Anyone at risk for tick bites Clinical Features: Fever, rigors, headache, arthralgias, myalgias, nausea, vomiting, malaise, fatigue Leukopenia, thrombocytopenia; slowly progressive anemia; Mild hepatitis; Rash in 36%; variable appearance, most often on trunk, legs, and/or arms Complications include: DIC, renal failure, seizures, coma (generally 7-10 days into illness) Serologic tests: Acute and convalescent sera for antibody testing;

28. Viral: Hepatitis C Key Facts: Most common reason for liver transplantation in U.S. adults; Responsible for 40% of chronic liver disease in U.S. Populations at risk: 1.Recipients of blood, organ or bone marrow transplants before 1992. 2.IV drug abusers. 3.People with high risk sexual practices and multiple sex partners. 4. Clinical workers and public safety workers exposed to blood, needles, by accident. 5.Infants of HCV infected mothers. 6.Long-term sexual partners (e.g. spouses) of HCV positive patients. Clinical Features: Initial infection asymptomatic; 85% of infections become chronic; fatigue is common;10-20% of chronic infections result in cirrhosis and 1-5% in hepatocellular carcinoma. Screening: EIA-2 (2nd generation enzyme immunoassay) for antibodies to HCV.

29. a strain of Streptococcus pyogenes (Group A streptococcus), a bacteria that, in severe cases, can destroy tissue as fast as surgeons can cut it out. claims the lives of up to 25% of its victims. In 1990, it was also responsible for the death of the famous puppeteer and creator of the Muppets, Jim Henson. Streptococcus pyogenes is responsible for a number of different diseases including: Streptococcal pharyngitis (Streptococcal sore throat). Scarlet fever. Skin infections Necrotising fasciitis or Streptococcal gangrene, the flesh-eating disease. Streptococcal toxic shock syndrome (STSS). Flesh eating bugs a strain of Streptococcus pyogenes (Group A streptococcus), in severe cases, can destroy tissue as fast as surgeons can cut it out. This organism claims the lives of up to 25% of its victims. In 1990, it was also responsible for the death of the famous puppeteer and creator of the Muppets, Jim Henson. Streptococcus pyogenes is responsible for a number of different diseases including: Streptococcal pharyngitis (Streptococcal sore throat). Scarlet fever. Skin infections Necrotising fasciitis or Streptococcal gangrene, the flesh-eating disease. Streptococcal toxic shock syndrome (STSS).

30. Other bacterial • Escherichia coli O157:H7: hemorrhagic diarrhea • Staphylococcus aureus/ S. pyogenes: toxic shock syndrome • Vibrio cholerae O-139:

31. Hantavirus Pulmonary Syndrome (Sin Nombre virus) Key Facts: First cases in the U.S. in New Mexico and Arizona in 1993; 205 confirmed cases in 29 states as of January 1999; Fatality rate is 45% by inhalation of aerosolized virus; Virus present in feces, urine, and saliva of asymptomatic rodents. Transmission by rodent bite possible; person to person transmission very unlikely Populations at Risk: 1.People living in rural and semi-rural areas. 2.People who have cleaned or otherwise disturbed rodent-inhabited barns, sheds, vehicles, or abandoned dwellings. 3.People who work in enclosed areas inhabited by rodents. 4.Hikers and campers who have disturbed rodent nests/burrows. Clinical Features: 3-6 day flu-like illness; rapid progression to hypoxia from non-cardiac pulmonary edema (ARDS) Diagnostic Testing: IgM ELISA test for antibodies to SNV

32. Fungal: PCP Pneumocystis carinii pneumonia, or PCP, is a severe illness found in people with HIV. It is caused by a germ called Pneumocystis carinii. People with HIV are less likely to get PCP today than in earlier years. However, PCP is still the most common serious infection among people with AIDS in the United States.

33. Epidemiology The study of when and where diseases occur and how they are transmitted in population

34. Types of Epidemiology Studies • Descriptive: Collections of data that describe the occurrence of the disease. • Analytical: usually done with a control method; data were statistically analyzed (base on genetic, environmental etc). • Experimental: based on a hypothesis about a particular disease; with a tested group and a control group.

35. Reporting the Notifiable diseases • Local clinicscity hospitals  State Health Department  Federal Health  World health organization. • Centers for Disease Control and Prevention (CDC) is the source of epidemiological information in the U.S. • Description of Morbidity rate (# of affected) and Mortality rate (# of death) due to a particular disease.

36. Example of Epidemiology study: Mapping bovine tuberculosis in Great Britain using environmental data