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Infectious Disease AS Supplement Infectious Disease An infectious disease is a transmissible disease resulting from the presence of pathogens including prions, viruses, bacteria, fungi, protozoa and multicellular parasites. These pathogens are able to cause disease in animals and/or plants. Slide 2 of 52 Pathogen Transmission Transmission can be Direct contact – directly from person to person Fluid transfer (HIV) Pathogen cannot survive outside of host Vector borne Malaria – Anopheles mosquitoes Water borne Cholera MattDamon Bourne Slide 3 of 52 Some Definitions Transmission cycle is the way in which a pathogen passes from one host to another. Control methods attempt to break the transmission cycle Major control methods Vaccination Barriers Sterilization of instruments Disinfecting or antiseptic procedures Slide 4 of 52 Some Definitions (Page 2) Incidence – Number of NEW cases in a time period Prevalence – TOTAL number of infected individuals Endemic – When the disease is always found in a population Prevalence may be high or low Epidemic – Sudden or dramatic increase in the incidence of a disease in an area or country Pandemic – Worldwide epidemic Slide 5 of 52 WHO (World Health Org.) Data Slide 6 of 52 Comparison by Income Slide 7 of 52 Pathogen Class & Disease Bacterial Viral TB (Tuberculosis) HIV / AIDS Protist Malaria Cholera Smallpox Measles Slide 8 of 52 Cholera (Overview) Caused by the bacterium Vibrio cholerae 3% death rate Water-borne Infection occurs by ingestion of fecal contaminated fluids or food Profuse diarrhea and vomiting Due to enterotoxin production (3 to 5 US gal) of diarrhea a day. High bacteria load in diarrhea (rice water) Slide 9 of 52 Cholera (Overview 2) Endemic in Africa and areas without access to If treated, recovery is quick If untreated, mortality > 50% Treatment Oral rehydration therapy (ORT) In severe cases Potassium replenishment due to acidosis Antibiotic therapy Doxycycline (Vibramycin) Slide 10 of 52 Cholera: Pathology The bacteria lodge in the small intestine & multiply Produce an enterotoxin called choleragen Disrupts epithelium functions by inhibiting a G-Protein This leads to excess salt exiting the epithelium into the intestinal lumen Now the intestinal lumen is hypertonic, so Excess water is secreted into the intestinal lumen from the epithelial linings AND the patient loses copious amounts of water via diarrhoea Can be fatal if untreated for 24 hours Slide 11 of 52 Cholera: Cause & Transmission Vibrio Cholerae (bacterium) is ingested Fecal contaminated of water or food Usually unclean water supply Especially in poor nations Sometimes oysters or shellfish If living in waters infected with human sewage Mainly found in wealthy nations Slide 12 of 52 Cholera is a top 10 cause of death, WHY? Very rare in the US Nearly all domestic cases (0-5 per year) are attributed to exposure abroad Common in recently industrialized countries Africa has the highest case fatality rate Large population migrations into urban centers in developing countries strain existing water and sanitation infrastructure and increasing disease risk. Cholera epidemics are a marker for poverty and lack of basic sanitation. An ongoing global pandemic in Asia, Africa and Latin America for the last four decades. 2010 Haiti outbreak following earthquake = 303 deaths Slide 13 of 52 Cholera is a social issue No sewage treatment or clean water in growing populations of developing countries No financial resources to tackle large municipal projects such as providing drainage system and clean water supply. Inadequate cooking or washing in contaminated water. Slide 14 of 52 Slide 15 of 52 Measles Highly contagious respiratory disease Measles virus = pathogen AND measles = disease Death Rate = 1-2 /1,000 7-10 day course of infection Rash throughout body and flu-like symptoms Children may spike high fevers Characterized by frequent complications & highly contagious nature Slide 16 of 52 Measles (Page 2) Transmitted via breathing, coughing or sneezing. CDC: “It is so contagious that any child who is exposed to it and is not immune will probably get the disease.” Easily prevented by a common childhood vaccine that is recommended for all children Slide 17 of 52 Measles Prevalence Prior to vaccine availability, almost every child in the US (and parts of Europe) contracted measles. Now, only sporadic cases remain in the US and other Americas. But deaths do occur in India and Asia 2010 Worldwide: 20 mil. cases AND 164,000 deaths Anti-vaccine movement Slide 18 of 52 Slide 19 of 52 Slide 20 of 52 Malaria Malaria is caused by the protoctist (protist) Plasmodium It is an Anopheles mosquito-borne infectious disease Anopheles is considered a vector (transmits the pathogen) Confined to tropical areas Slide 21 of 52 Mosquito Vector The female Anopheles mosquitoes feed on human blood to obtain protein Plasmodium may be present in Anopheles’ saliva, so a bitten by an infected Anopheles, may take up some of the plasmodium. The female is only sucking blood, so how does the plasmodium get injected into the human? Once in the blood, the plasmodium parasites travel to the liver to mature and reproduce. Slide 22 of 52 Mosquito Vector (Page 2) The infective stages of the Plasmodium enter the red blood cells, where they multiply. When the infected mosquito feeds again, it injects an anti-coagulant into the blood meal so that it flows out from the host into the mosquito. Slide 23 of 52 Clarification… How does a vector differ from a pathogen? Can you get infected from a mosquito bite, when the mosquito does not harbor the plasmodium parasite? Can you get infected from a male mosquito bite, when the mosquito has the plasmodium parasite? Slide 24 of 52 Slide 25 of 52 Slide 26 of 52 Prevention of Malaria The three main ways to control malaria: 1. Reduce the number of mosquitoes (destruction of breeding ground, stagnant water, the use of insecticides) 2. Avoid mosquitoes bites (using fly screens, mosquito repellents) 3. Use prophylactic drugs to prevent infection (chloroquine and quinine, proguanil, mefloquine). Slide 27 of 52 Current Issues in Malaria Treatment An increase in drug-resistance forms of Plasmodium. An increase in proportion of cases caused by Plasmodium falciparum (more lethal form) Difficulties in developing a vaccine An increase in the number of epidemics because of climatic and environmental changes that favours the spread of mosquitoes (Global Warming is bad?) the migration of people as a result of civil unrest and war. Slide 28 of 52 Slide 29 of 52 HIV / AIDS AIDS = Acquired Immune Deficiency Syndrome (NOT Disease) Due to a collection of opportunistic infections Caused by the retrovirus HIV (Human Immunodeficiency Virus) HIV Disease is caused by HIV pathogen HIV infects Helper T-cells CD4 cells Involved in which acquired immunity? So how is it pathological? Slide 30 of 52 -- 2 copies of ssRNA = viral genome -- Has reverse transcriptase (Why?) -- Proteases for exiting cells -- Glycoprotein 120 and 41 in envelope -- p24 in the conical capsid Slide 31 of 52 Slide 32 of 52 HIV / AIDS Pathology HIV infection results in the gradual destruction of the immune system by destroying the CD4 cells and macrophages Since the immune system is compromised, patients are susceptible to Opportunistic Infections (OIs) Patients cannot defend against OIs, and die ultimately of the OI, but really died due to the loss of immune system functionality Slide 33 of 52 Slide 34 of 52 HIV Disease Infection is characterized by a brief flu-like disease Called Acute HIV syndrome 2-4 weeks following exposure Clinical Latency Patient will be asymptomatic for multiple years 3-20 years after exposure Progressive appearance of symptoms People may not know they are HIV carriers Slide 35 of 52 AIDS Following the progressive degeneration of the immune system, eventually the patient runs out of T-cells Diagnosis: T-cell (CD4) count < 200 Coincides with the appearance of an OI End stage of HIV disease PCP – pneumocystis Carnii pneumonia (40%) Esophageal Candidiasis, wasting disease Viral induced cancers (Kaposi’s sarcoma) Slide 36 of 52 Transmission Unprotected sexual intercourse Primarily anal (0.03-3.00% risk) and vaginal (0.05-0.30%) Risk varies dramatically between high risk (low income countries) and lower risk (high income countries) Exposure to bodily fluids or tissues (blood to blood) Birth (25% risk) Risk can be reduced to 1% with Anti-Retroviral Therapy Intravenous drug usage (0.67%) Inappropriate syringe usage in sub-Saharan Africa Blood transfusions (90%) Slide 37 of 52 Social Issues HIV infection weakens the immune system thus people are more vulnerable to malnutrition, TB and malaria. AIDS cause an adverse effect on the economic development of countries Purchase of expensive drugs drains government funds AIDS has reversed 10-15 years of economic growth for some African states. Slide 38 of 52 Treatment No cure and no vaccine for HIV Drug therapy can slow down the onset of AIDS The drugs have side effects and are expensive. Two or more drugs (combination therapy) can prevent the replication of the virus inside the host cells. Delays progression of the disease May lead to atherosclerosis and cardiomegalopathy The pattern and timing of medication through the day must be strictly followed. Slide 39 of 52 Slide 40 of 52 Global Distribution of HIV Slide 41 of 52 Tuberculosis Tubercle Bacillus (TB) Tubercle is a round nodule or wart-like structure Mycobacterium = pathogen Airborne An invasive disease - it starts with a primary infection in the lungs and quickly spreads to the lymph nodes, bones and gut. It often strikes HIV-positive people when their immune system begins to weaken. Slide 42 of 52 Slide 43 of 52 Characteristics Most commonly affects the lungs (pulmonary TB) but can also affect the CNS, lymphatic system, and even skin. Some people become infected and develop TB quite quickly, whilst in others the bacteria remain inactive for many years. People with this inactive infection do not spread the disease to others. But the bacteria become active when these people are weaken by other diseases, suffer from malnutrition or become infected with HIV. Slide 44 of 52 Transmission Method Generally, it is spread via airborne droplets, and is particularly prevalent in overcrowded areas, and people suffering malnutrition are more susceptible. TB is spread when infected people with the active form of the illness cough or sneeze The bacteria are carried in the air in tiny droplets of liquid. Slide 45 of 52 Slide 46 of 52 TB due to Bovine? M. Bovis also causes tuberculosis and occurs in cattle, it can be spread via their meat and milk, but both bacterium infections have fallen now because of vaccine introduction in the 1950s. People can also contract TB from cattle through airborne droplets Pasteurization has made this virtually irrelevant Slide 47 of 52 Treatment Diagnosis - sputum sample is searched by microscope for identification of the tuberculosis bacteria Treatment always involves patient isolation Treatment involves multiple antibiotics to ensure that all bacteria are killed, especially the drug resistant strain of the bacterium. Long course of treatment (9 months to a year) Incomplete treatment course may lead to infecting others with drug-resistant forms (evolved) of TB. Slide 48 of 52 TB Resistance Tuberculosis is unfortunately showing a comeback, and this is thought to be due to a variety of factors. These include; Breakdown in the vaccination and control program Poor housing causing overcrowding The AIDS epidemic weakening immune systems and allowing it to be more prevalent Some strains are now resistant to antibiotics Multiple Drug Resistant (MDR-TB) & Extremely Drug Resistant (XDR-TB) Slide 49 of 52 TB Prevalence Slide 50 of 52 TB Mortality Slide 51 of 52 Current Issues Frontline “TB Silent Killer” in Swaziland NDM-1 plasmid gene NDM-1 was first detected in a Klebsiella pneumoniae isolate in 2008. It was later detected in India, Pakistan, the UK, US, Canada, and Japan Escherichia coli and Klebsiella pneumoniae, but the gene for NDM-1 can spread from one strain of bacteria to another by horizontal gene transfer. Slide 52 of 52