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TRANSCRIPT
Infectious diseases
• Pathogens – bacteria, viruses, protozoans, fungi, and other parasites capable of causing change that dirsrupts homeostasis in the body
• Infectious diseases - Any disease caused by the presence of pathogens in the body
• main sources of pathogens:– soil
– contaminated water
– infected animals/people
Infectious diseases
• Not all microorganisms are pathogenic
• body is host to billions of microorganisms (mostly bacteria)
• have a symbiotic relationship with the body helping to keep harmful bacteria and other microorganisms from growing
Normal microflora
Normal Micro flora & its importance
1. Prevent the growth of pathogens
2. Stimulate the immune system to produce antibodies that cross-react with invading pathogens
3. Aid in digestion of cellulose in ruminants
4. Produce essential nutrients
Koch’s Postulates
1. same pathogen must be present in every case of the disease
2. The pathogen must be isolated from the diseased host and grown in pure culture
3. The pathogen from the pure culture must cause the disease when introduced into a healthy but susceptible organism
4. The pathogen must be isolated from the inoculated animal and be shown to be the original organism.
Koch’s Postulates: modifications
1. Some infectious agents cannot be cultured e.g. prions
2. Some pathogens have non-virulent strains whose presence does not link them to a disease. E.g. non encapsulated Diplococcuspneumoniae
Types of Pathogens
1. Bacteria
a. Gram positive (S. aureus, S. pneumoniae)
b. Gram negative (Y. pestis, Salmonella typhi)
Types of Pathogens
2. Parasites (Eukaryotic Pathogen)
a. Fungi
e.g. Candida, Aspergillus
b. Protozoa
e.g. Plasmodium, Schistosoma
c. Worms
e.g. Ascaris, Taenia
Candida
Plasmodium
Ascaris
Types of Pathogens
3. Viruses
• Are pieces of DNA or RNA surrounded by protein coat.
• Encapsulated e.g. HIV, HBV, measles, mumps, influenza, rabies
• Non-encapsulated e.g. adenoviruses, HPV, Polio
rabies
polio
Modes of transmission
• Direct contact – touching, handshaking, or sexual
intercourse
• Indirect contact – food, water or droplets in air;
• Animal vectors– insect bites in malaria, plague and,
dog bite in rabies
Reservoirs of pathogens
Humans
• carriers are a significant reservoir of infectious disease
• communicate the disease before experiencing symptoms
Animals
• other main reservoir for pathogens, making the eradication of certain pathogens almost impossible
Pathogenesis
Sequence of activities
1. Transmission of causative
agent to susceptible host
2. Adherence of the agent to a
target tissue
3. Colonization and invasion
4. Damage to host by toxins or
other mechanisms
• Pathogenicity - the potential capacity of certain species of microbes to cause a disease (ability to cause disease)
• Virulence - degree of pathogenicity within a group or species of parasites as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host
Virulence factors - molecules expressed and secreted by pathogens (bacteria, viruses, fungi and protozoa) that allow them to:
• colonize of a niche in the host (this includes adhesion to cells) for example
• evade the host's immune response (Immunoevasion)
• inhibit the host's immune response (Immunosuppression)
• obtain nutrition from the host
Pathogenicity of an organism is determined by its virulence factors
Virulence factors
factors that confer pathogenicity include
• Pili that facilitate attachment
• Capsules that interfere with phagocytosis
• Exotoxins
• Endotoxins
• Proteases that break down antibodies
• Ability to vary antigens to evade antibodies
Endotoxin Exotoxin
• Lipopolysaccharide
• Gram (-)
• Can’t act as enzymes
• part of the outer membrane of cell wall
• less toxic
• Heat stable
• Poor antigens
• Soluble protein
• Gram (+) and (-)
• Can act as enzymes
• are extracellular component
• More toxic
• Not heat stable
• antigenic
Malaria
1. Causative Agent: Plasmodium (4 species)
2. Symptoms (Clinical features): fever, chills, anaemia, headache, nausea, shivering, convulsions (esp. in under 5 yrolds) enlarged spleen.
3. Pathogenesis: site of action of pathogen include: liver, RBC, brain.
4. vector, female Anopheles mosquito, transfer pathogen during feeding
5. Epidemiology: Endemic in 91 tropical and subtropical countries. Invade the liver 1st and move to reproduce in RBCs resulting in their rupture and the associated chills.
6. Incubation Period: 1 – 2 weeks.
7. Lab diagnosis: Microscopy.
Malaria
Infected RBCs
• Reduce the number of mosquitoes; destruction of larvae and adult mosquitoes by biological and chemical control methods
• Avoid being bitten; protective clothing and creams, treated bed nets
• Use of drugs to prevent infection; chemoprophylaxis
• Combination therapy: Artesunate Amodiaquine
Malaria prevention
Emerging infectious diseases
Newly identified & previously unknown infectious agents that cause public health problems either locally or internationally
Re-emerging infectious disease
Infectious agents that have been known for some time, had fallen to such low levels that they were no longer considered public health problems & are now showing upward trends in incidence or prevalence worldwide
Factors contributing to emergence
Infectious agent
• Evolution of pathogenic infectious agents
(microbial adaptation & change)
• Development of resistance to drugs
• Resistance of vectors to pesticides
Factors contributing to emergence
Host
• Human demographic change (inhabiting new areas)
• Human behavior (sexual & drug use)
• Human susceptibility to infection (Immunosuppression)
• Poverty & social inequality
Factors contributing to emergence
Environment
• Climate & changing
ecosystems
• Economic development &
Land use (urbanization,
deforestation)
• Technology & industry (food
processing & handling)
• International travel &
commerce
• Breakdown of public health
measure (war, unrest,
overcrowding)
• Deterioration in surveillance
systems (lack of political will)
Animals to Humans transmission
• More than 75% emerging infections originate from animals-wild & domestic
• Emerging Influenza infections in Humans associated with Geese, Chickens & Pigs
• Animal displacement in search of food after deforestation (Yellow fever, Malaria)
Poverty, Neglect & Weak Health Infrastructure
• Poor populations- major reservoir & source of continued transmission
• Poverty- Malnutrition- Severe infectious disease cycle
• Lack of funding, Poor prioritization of health funds, curative vs. preventive infrastructure
• Failure to develop adequate health delivery systems
Dr. KANUPRIYA CHATURVEDI
Uncontrolled Urbanization & Population Displacement
• Growth of densely populated cities- substandard housing, unsafe water, poor sanitation, overcrowding, indoor air pollution (>10% preventable ill health)
• Problem of refugees & displaced persons
• Diarrheal & Intestinal parasitic diseases
Dr. KANUPRIYA CHATURVEDI
• Unsafe sexual practices (HIV, Gonorrhoea, Syphilis)
• Changes in agricultural & food production patterns- food-borne infectious agents (E. coli)
• Increased international travel (Influenza)
• Outdoor activity
Human behavior
Dr. KANUPRIYA CHATURVEDI
Causes:
• Wrong prescribing practices
• non-adherence by patients
• Counterfeit drugs
• Use of anti-infective drugs in animals & plants
Antimicrobial drug resistance
Dr. KANUPRIYA CHATURVEDI
Consequences
• Prolonged hospital admissions
• Higher death rates from infections
• Requires more expensive, more toxic drugs
• Higher health care costs
Antimicrobial drug resistance
Dr. KANUPRIYA CHATURVEDI
Examples of recent emerging diseases
Source: NATURE; Vol 430; July 2004; www.nature.com/nature
Dr. KANUPRIYA CHATURVEDI
Dealing with emerging diseases
• Surveillance at national, regional, global level• epidemiological
• laboratory
• ecological
• Anthropological
• Investigation and early control measures
• Implement prevention measures• behavioural, political, environmental
• Monitoring, evaluation
Dr. KANUPRIYA CHATURVEDI
Public health surveillance & response systems
• Rapidly detect unusual, unexpected, unexplained disease patterns
• Track & exchange information in real time
• Response effort that can quickly become global
• Contain transmission swiftly & decisively
Proposed solutions
Dr. KANUPRIYA CHATURVEDI
• Internet-based information technologies– Improve disease reporting
– Facilitate emergency communications &
– Dissemination of information
• Human Genome Project– Role of human genetics in disease susceptibility,
progression & host response
Dealing with emerging diseases
Dr. KANUPRIYA CHATURVEDI
• Microbial genetics– Methods for disease detection, control & prevention
• Improved diagnostic techniques & new vaccines
• Geographic Imaging Systems– Monitor environmental changes that influence
disease emergence & transmission
Dealing with emerging diseases
Dr. KANUPRIYA CHATURVEDI
• Coordinated, well-prepared, well-equipped PH systems
• Partnerships- clinicians, laboritarians & PH agencies
• Improved methods for detection & surveillance
Dealing with emerging diseases
Dr. KANUPRIYA CHATURVEDI
• Effective preventive & therapeutic technologies
• Strengthened response capacity
• Political commitment & adequate resources to address
• underlying socio-economic factors
• International collaboration & communication
Dealing with emerging diseases
Zombies: 28 Weeks Later
Zombie infection: group activity (wine making)
• From the film 28 Weeks Later characterize
• Causative agent• symptoms• Mode of transmission/pathogenesis• Vector• Incubation period• Virulent factors• Epidemiology• Diagnosis method
• What real life infectious agent/s does the one in the movie resemble?
• How would you prevent spread of infection?
• How would you eradicate the causative agent?
Infectious Disease Terms
1. Epidemiology
2. Epidemic
3. Endemic
4. Pandemic
5. Pathogen
6. Opportunist
7. Nosocomial
8. virulence
Yersinia pestis
• Gram-negative rod-shaped coccobacillus
• facultative anaerobe that can infect humans and other animals
• Vector: fleas• Proteins from the bacteria form a biofilm in the proventriculus of
the flea• biofilm contains aggregated bacteria and blood clot• Biofilm prevents the fleas from feeding: ingested blood dislodges
the bacteria in the esophagus and regurgitated into bitten animal (rodents)
• Reservoir host/carriers: rodents
Yersinia pestis
• Fleas to human: bites of fleas carrying Y. pestis allow the bacteria to overcome the skin barrier
• virulence factors are anti-phagocytic in nature
• Has the ability to suppress and avoid normal immune system responses such as phagocytosis and antibody production
• proliferates inside lymph nodes where it is able to avoid destruction by cells of the immune system
Scanning electron micrograph of a phagocyte (yellow, right) engulfing anthrax bacilli (orange, left)
cholera
1. Causative Agent: Vibrio cholerae
2. Symptoms: severe diarrhoea up to 20 liters a day of “rice water stool”, vomiting, muscle cramps caused by loss fluid and electrolytes.
3. Pathogenesis: Vibrio adheres to the small intestinal lining, multiply and produce the enterotoxin choleragen which causes the accumulation of cAMP. An increased secretion of water and electrolyte from the cells results
Cholera
4. Epidemiology: Feacally contaminated
water, crabs and vegetables fertilized
with human faeces. Has been eradicated
most developed countries but a new
strain discovered in 1992 is threatening
another pandemic.
Cholera
5. Incubation period: 12-48 hours
6. Lab diagnosis: Microscopy, culture of
sample from faeces or vomit.
7. Prevention: Purification of water, washing
of hands.
8. Treatment: administration of solution of
glucose and electrolyte orally or
intravenously; tetracycline antibiotic orally
Tuberculosis
1. Pathogen: M. tuberculosis (pulmonary TB);
M. bovis(GI TB)
2. Transmission: airborne droplets (NB MTB is
dessication resistant and survives in dried
sputum); unpasteurized milk.
3. Clinical features: prolonged coughing
sometimes with bloody sputum, shortness of
breath, fever, sweating , weight loss
Tuberculosis
4. No toxin production. Pathogenicty is by invasiveness that produce characteristic lesions in the lungs.
5. Epidemiology: pathogen triggers acute inflammatory response + forms tubercle –giant cells containing MTB and surrounded by epithelial cells. Tubercles heals by fibrosis and calcification. Can desseminate via bloodstream to other internal organs