gchCH6 - Chapter 6: Chapter The Spread of The Infectious...

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Unformatted text preview: Chapter 6: Chapter The Spread of The Infectious Diseases Infectious Modes of Transmission Modes Direct (person-to-person) transmission – – – – Contact with blood or body fluids Sexual contact IDU (injecting drug use) Fecal-oral spread Airborne Vector-borne: spread by an insect or other animal Vehicle-borne: spread by inanimate objects Vehicle-borne: (fomites) (fomites) – Food- or water-borne Mother-to-child (MTC) / vertical Examples for each… Reservoir Reservoir Where in the ‘environment’ is the infection Where found? found? Soil Water Humans (anthroponosis) Animals (zoonosis) Examples for each… Cycle of Infection Cycle Human – human – human Vertebrate – vertebrate – human Insect - human – insect – human Complex cycles Examples for each… Infection & Disease Infection Infection: agent reproduces inside a agent person person Not all exposures cause an infection. – Infectivity: # iinfected / # exposed (and nfected susceptible at time of exposure) susceptible Not all infections cause disease Not (symptoms). (symptoms). – Pathogenicity: # ill (symptomatic) / # infected Natural History of Disease Infection occurs time Disease could be detected through testing Pre-clinical phase Symptoms of disease develop Symptoms resolve or the infected person dies Clinical phase (incubation period) The infected person may become contagious before the onset of symptoms Natural History Natural Acute: short-term Chronic: long-term Some chronic infections cause cancer: – HPV cervical cancer HPV – Hepatitis C liver cancer Hepatitis – Schistosomaisis bladder cancer Schistosomaisis Infection Outcomes Infection Susceptible Infected Recovery Susceptible Death Immune An infection that has a high case fatality rate is said to have high virulence (# dead / # sick). Agent – Host- Environment Triad Agent Agent Agent What makes an infectious agent unique? – Type (strain) – Mode of transmission, reservoir, etc. – Drug resistance Infectious Agents Infectious Bacteria Viruses Fungi Parasites – Protozoa – Helminths (worms) – Others Bacteria Bacteria Shapes: rods (bacilli), spheres (cocci), Shapes: spirals (spirochetes, vibrios, spirilla) spirals Gram-positive vs. gram-negative based on Gram-positive peptidoglycan in cell walls peptidoglycan Found everywhere from arctic to hot Found springs in ocean springs Helpful: decomposition, nitrogen fixation in Helpful: plants, making cheese & yogurt & alcohol, aiding digestion aiding Bacterial Diarrhea Bacterial E. coli Cholera (Vibrio cholerae) Typhoid (Salmonella typhi) Other Salmonella Other Salmonella Shigella Campylobacteria Typhus Typhus Typhus – Transmission: rodent fleas – Symptoms: Fever, rash, and high mortality Symptoms: rate rate – Not typhoid (diarrhea)! Plague Plague Transmission: rodent flea Symptoms: Symptoms: – Bubonic plague: swollen lymph nodes Bubonic (“bubos”) (“bubos”) – Pneumonic plague: severe pneumonia Lyme Disease Lyme Transmission: bite of deer tick Symptoms: bulls-eye rash (in some cases) Symptoms: arthritis and neurologic symptoms if untreated untreated Brucellosis Brucellosis a.k.a. Undulant fever, Malta fever Transmission: unpasteurized dairy Transmission: products products Symptoms: Chronic fevers Bacterial STIs (Sexually Transmitted Infections) (Sexually Chlamydia Gonorrhea – Often asymptomatic but can cause scarring Often and pain in women (PID: pelvic inflammatory disease) disease) Syphilis – 3 stages: (1) rash or chancre (2) rash stages: (3) weak arteries and nervous system impairment impairment Trachoma Trachoma Caused by a type of chlamydia infection #1 cause of infectious blindness Prevention: wash face daily TB and Hansen’s disease TB Both caused by Mycobacterium Both Mycobacterium TB (M. tuberculosis): usually affects lungs Hansen’s disease / leprosy (M. leprae): ): can cause disfigurement because of nerve damage damage Antibiotics taken for months to years will Antibiotics cure infection cure “Childhood” Bacterial Illnesses Pertussis (whooping cough) Tetanus (lockjaw) Antibiotic Resistance Antibiotic MRSA (methicillin-resistant Staph aureus) MRSA Staph MDR-TB (multidrug-resistant TB) Only take antibiotics (antimicrobials) when Only you have an infection that can be cured by them them Finish all pills as prescribed Viruses Viruses Technically not alive – take over your cells Technically and use them to replicate and Common examples: colds, influenza “Childhood” Viral Illnesses Measles Mumps Polio (infantile paralysis) Rubella (German measles): can cause Rubella birth defects if pregnant women become infected during 1st trimester infected Viral STIs Viral HIV Herpes Hepatitis C virus: can cause liver cirrhosis Hepatitis and increases risk of liver cancer and – No vaccines; interferon may suppress No interferon infection but will not cure it not Human papillomavirus (HPV): causes Human warts and can cause cervical cancer warts – Vaccine now available Rabies Rabies Transmission: mammal bites (saliva) Symptoms: nervous system impairment Symptoms: hydrophobia and death hydrophobia Without PEP (post-exposure prophylaxis) Without PEP rabies is 100% fatal rabies Yellow Fever Yellow Transmission: Aedes aegypti mosquitoes Transmission: Aedes Symptoms: jaundice (yellow skin because Symptoms: of liver problems) of Mandatory vaccine for travel to many Mandatory countries countries Dengue Fever Dengue Transmission: mosquitoes 4 serotypes (strains) Infection with 1st serotype – severe headache & fever headache Infection with 2nd serotype – may cause DHF (dengue hemorrhagic fever) DHF Vaccine must be effective against all 4 Vaccine serotypes serotypes Emerging Infections Emerging FYI: more on HIV/AIDS, malaria, and TB FYI: in chapter 7 in FYI: more on emerging infections & FYI: bioterrorism in chapter 8 bioterrorism – Anthrax – Hantavirus – Influenza – Marburg virus – West Nile virus Protozoa Protozoa Single-celled organisms that live in water Examples: Paramecium and Amoeba Examples: Paramecium Amoeba Protozoan-Diarrhea Protozoan-Diarrhea “Epidemic diarrhea” Amoebic dysentery Cryptosporidiosis (“crypto”) – 1993 Milwaukee outbreak Giardia Malaria Malaria 4 types of Plasmodium parasites types Plasmodium Transmitted by female Anopheles Transmitted mosquitoes mosquitoes More in chapter 8 Trypanosomiasis Trypanosomiasis Trypanosomiasis (African sleeping Trypanosomiasis sickness) sickness) – Spread by tsetse fly bites – Chronic fevers paralysis and death Chronic – Fatal without treatment – 50,000+ cases each year Trypanosomiasis Trypanosomiasis Chagas disease (American sleeping Chagas sickness) sickness) – Spread by feces of “kissing bugs” that enter Spread bite wounds, often near eye bite – 1/3 of infected develop chronic infection that 1/3 damages heart and digestive tract damages Leishmaniasis (“leish”) Leishmaniasis Spread by sand fly bites Cutaneous (skin) form causes lesions that Cutaneous may lead to disfigurement may Visceral form, called “kala azar,” causes Visceral chronic disease swelling of spleen and liver death within a few years if untreated untreated Parasites Parasites Ectoparasites: llice, mites (that cause ice, scabies), and animals that live outside the outside body body Endoparasites: iintestinal worms, blood ntestinal and liver flukes, and other animals that live inside the body inside – May live nearly anywhere in the body – Contracted through soil (STH: soil-transmitted STH: helminth), food, water, contact with feces, etc. helminth Intestinal Worm Infections Intestinal Examples: – Pinworms – Tapeworms – Trichinosis – Flatworms (“flukes”) – Roundworms (STH) - Ascariasis – Whipworms (STH) - Trichuriasis – Hookworms (STH) Soil Transmitted Helminths Soil Public Health Problem Transmission Occurs Hookworm Hookworm Contracted by walking barefoot in soil Hook into intestine bleeding Hook anemia anemia Dracunculiasis (Guinea worm) Dracunculiasis Caused by drinking water that contains Caused larva-infected water fleas larva-infected Worm grows to about 3 feet then slowly & Worm painfully emerges (1cm/day) painfully Prevent by filtering water and keeping Prevent infected people away from water sources infected Onchocerciasis (“Oncho”) – River Blindness River Transmitted by black flies Adult worms form nodules under skin Nodules near eyes cause blindness Treat with drug (ivermectin) Lymphatic filariasis (LF) Lymphatic Spread by mosquito bites Causes swelling of body parts (often arm, Causes leg, or scrotum) when worms block flow of lymph (fluid from tissues) lymph “Elephantiasis” >100 million people worldwide infected Schistosomiasis (“Schisto”, Bilharzia) (“Schisto”, Worm enters body through skin causes Worm bladder or intestinal damage & increased risk of cancer risk Worms cycle between snails and humans Worms (“snail fever”) (“snail Prevention: molluscicides Treatment: drug (praziquantel) Increased prevalence with dam-building Fungi Fungi Molds and yeasts May be helpful: bread, wine, cheese Fungal infections often develop when Fungal normal balance of helpful microflora disturbed by antibiotic use or immunosuppression immunosuppression Candidiasis – too much Candida albicans Candidiasis Candida causes thrush, diaper rash, yeast infections infections Ringworm (Athlete’s foot, jock itch, tinea) Host Host Age Sex Genetic makeup Biology: immune status, pregnancy, co- morbidities, stress, nutrition SES Behavior: drug / alcohol use, diet, physical Behavior: activity, sexual practices, hygiene, use of health resources health Environment Environment Natural environment: geography, climate, Natural weather, plants / animals, etc. weather, Community / occupational environment: Community water, waste, chemicals, pollutants, noise, etc. etc. Social, political, economic environment: Social, access to transportation, communication, education, health services, institutions, etc. etc. Agent – Host- Environment-Vector Triad Agent Measuring Disease in Populations Measuring Incidence = # new cases / people at risk new – Often used for acute and infectious diseases Often or injuries or Prevalence = # total cases / all people in total the population the – Often used for chronic and noncommunicable diseases December 31, 2004 December 31, 2005 At the end of 2004, there were 100 adult residents of Villagetown and 20 of them had HIV infection. At the start of 2005 there were 80 susceptible adults in Villagetown. During 2005, 8 became newly infected with HIV. The prevalence of HIV infection was 20/100 = 20%. The one-year incidence rate of HIV infection was 8/80 = 1/10. One in 10 susceptible adults became infected. Assuming that all of the adults survived to the end of 2005, there were 100 adult residents of Villagetown and 28 of them had HIV infection. The prevalence of HIV infection was 28/100 = 28%. Epidemics Epidemics Endemic: always present Epidemic: more cases than normal Pandemic: global epidemic Surveillance: tracking infectious disease tracking reports to catch outbreaks early reports – Often look for clusters in time or space Often clusters Immunity Immunity Active immunity from past infection or vaccination “memory” immune cells form and provide long-term protection form Passive immunity from breastmilk or Ig (immunoglobulin) shot temporary protection (a few months) protection Herd immunity: not everyone in a not population has to be vaccinated to protect “the herd” “the Disease Control Disease Control: limit infection within an area Elimination: no new cases of the infection no in the area in Eradication: no new cases anywhere in no the world the – Smallpox (1979) – Next: Polio? Dracunculiasis? Dracunculiasis Incidence Dracunculiasis 500000 400000 300000 200000 Number of Cases 100000 0 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Ye a r Nearing eradication ...
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This note was uploaded on 09/23/2011 for the course GCH 100 taught by Professor Corso during the Fall '11 term at George Mason.

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