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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.

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infectious disease

Infectious Disease

AS Supplement

infectious disease1
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.
pathogen transmission
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
some definitions
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
some definitions page 2
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
cholera overview
Cholera (Overview)
  • Caused by the bacterium Vibriocholerae
  • 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)
cholera overview 2
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)
cholera pathology
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
cholera cause transmission
Cholera: Cause & Transmission
  • VibrioCholerae (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
cholera is a top 10 cause of death why
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
cholera is a social issue
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.
  • 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
measles page 2
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
measles prevalence
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
  • 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
mosquito vector
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.
mosquito vector page 2
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.
  • 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?
prevention of malaria
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).

current issues in malaria treatment
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.
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?

-- 2 copies of ssRNA = viral genome -- Glycoprotein 120 and 41 in envelope

-- Has reverse transcriptase (Why?) -- p24 in the conical capsid

-- Proteases for exiting cells

hiv aids pathology
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
hiv disease
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
  • 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 – pneumocystisCarnii pneumonia (40%)
    • Esophageal Candidiasis, wasting disease
    • Viral induced cancers (Kaposi’s sarcoma)
  • 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%)
social issues
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.
  • 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.
  • 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.
  • 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.
transmission method
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.
tb due to bovine
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
  • 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.
tb resistance
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)
current issues
Current Issues
  • Frontline “TB Silent Killer” in Swaziland
  • NDM-1 plasmid gene
    • NDM-1 was first detected in a Klebsiellapneumoniaeisolate in 2008. It was later detected in India, Pakistan, the UK, US, Canada, and Japan
    • Escherichia coli and Klebsiellapneumoniae, but the gene for NDM-1 can spread from one strain of bacteria to another by horizontal gene transfer.