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• Emerging disease


  A disease that has appeared in a population for the first time, or that may have existed previously but is rapidly increasing in incidence or geographic range
• Re-emerging disease


  A disease whose incidence has increased in a defined time period and location
• What is NOT a re-emerging disease is an outbreak or seasonal variation
• Some key terminology


  • Transmission: The mechanism in which a disease is spread i.e. faeco-oral, vector borne, etc.
  • Incubation period: The time between infection and symptom onset.
  • Carrier: A person or animal without apparent disease who harbours a specific infectious agent and is capable of transmitting it to others.
  • Infectivity: The proportion of persons exposed to a causative agent who become infected by an infectious disease.
  • Reservoir: The habitat in which an infectious agent normally lives, grows and multiplies; can include human reservoirs, animals reservoirs, and environmental reservoirs.
  • Zoonoses: An infectious disease that is transmissible under from animals to humans.
  • Endemic: A disease which is constantly present in a population or geographical area.
  • Epidemic: The occurrence of more cases of disease than expected in a given area or population over a particular period of time.
  • Pandemic: Worldwide epidemic, effecting a large, widespread population simultaneously
• Lyme Disease


  • Family: Spirochaetaceae
  • Species: Borrelia burgdorferi
  • Structure: spirochete (coiled, double membrane)
  • Growth: microaerophilic
  • Transmission: zoonotic reservoir, vector borne transmission - bite of infected black legged tick
  • Virulence Factor: flagella; motile; exploiting immune system; OspC lipoprotein expression
  • Risk Factors: white; male; age 5-14 or 50-70
  • Dangerousness Score: 10/12
• Lyme disease emerged in the 1960s and is continuing to expand
• Lyme Disease: transmission cycle


  1. Blacklegged ticks have a 2-to-3-year life cycle going through egg, larva, nymph and adult female stages

  2. Larva and nymph each must take a blood meal to develop to the next life stage, and the female needs blood to

  3. Many species secrete a cement-like substance that keeps them firmly attached during the meal

  4. The feeding tube can have barbs which help keep the tick in place

  5. Ticks also can secrete small amounts of saliva with anaesthetic properties so that the animal or person can't feel that the tick has attached itself

  6. Contract when feeding on an infected wildlife host

  7. Nymphs or adult females can then spread the bacteria during their next blood meal

  8. A tick must be attached for 36 to 48 hours or more before the Lyme disease bacterium can be transmitted

  9. If you remove a tick quickly chances of getting Lyme disease is reduced

  10. Nymphal ticks pose a particularly high risk due to their abundance and small size

  11. Adult female ticks also can transmit the bacteria but because of their larger size
• Lyme Disease: virulence factors


  • B. burgdorferi expresses Outer Surface protein A (OspA) used for attachment to tick mid-gut
  • B. burgdorferi expresses OspC due to nutrients in gut, detaches and becomes motile, secreted in tick saliva
  • B. burgdorferi enters vertebrate host epithelium & migrates into tissue & joints
• Lyme disease: treatment and prevention


  • No human vaccine
  • Reduce exposure to tick bites
  • Personal protection, deer and land management, acaricides, education
  • Can be treated with doxycycline if caught early
  • Need improved treatment for chronic symptoms
  • Improved diagnostics needed for early treatment
• Cholera


  • Causative agent: Vibrio cholerae 01 El Tor
  • Characteristics: Gram negative, Facultative anaerobe, comma shaped rod, Flagellated
  • Transmission: contaminated water (and food)
  • Virulence factor: cholera enterotoxin; Adherence factors (Hemagglutinins)
  • Dangerousness Score: 11
• Cholera: pathology


  • Causes sudden and dramatic 'rice water' diarrhoea, due to the effect of the toxin
  • Cholera toxin causes Cl- ions to be excreted from cells of the intestine and reduces the re-absorption of NaCl
  • Osmotic pressure draws water into the lumen of the gut which manifests as watery diarrhoea
  • Death can occur due to excretion of 0.5 to 1l/h of diarrhoea, leading rapidly to tachycardia, hypotension, and vascular collapse due to dehydration
• Cholera is endemic in many countries and has led to 6 global pandemics, killing millions
• Cholera re-emergence linked to increasing size of vulnerable populations living in unsanitary conditions
• Cholera: Haiti epidemic in 2010


  • Natural disaster - earthquake
  • Plot shows outbreak over 3 different areas following arrival of Nepalese government forces on Oct 9th (Nepal outbreak began 23rd Sept)
  • Leading to epidemic in Haiti
• Cholera: treatment and prevention


  • Preventable with safe water and sanitation
  • Cholera vaccine: Vaxchora®, Dukoral, Shancho
  • Rehydration therapy: Oral or intravenous; salts and mineral replacement
  • Antibiotic treatment
  • Zinc treatment
  • Surveillance and rapid responses to outbreaks needed
• Shigella spp.


  • Family: Enterobacteriaceae
  • Characteristics: Gram negative, Facultative anaerobe, Non-motile
  • Transmission: food, water, reduced hygiene
  • Virulence factors: invasion of epithelial cells, shiga (vero) toxin production
  • Dangerousness Score: 7
• Shigellosis represents a major burden of disease, especially in developing countries, estimated to affect at least 80 million persons, predominantly children, each year
• Disease may be caused by any of the 4 Shigella species: S. dysenteriae, S. flexneri, S. boydii and S. sonnei
• Ratio of S. sonnei to S. flexneri is increasing
• Multidrug resistant (MDR) isolates detected in 83.8% of S. sonnei, 78.5% of S. flexneri, 60.6% of S. dysenteriae, and 64% of S. boydii isolates
• Most recent resistance is to ciprofloxacin, with resistant isolates found from 2008
• Emerging and re-emerging bacterial diseases are a national and international concern
• Epidemiology is crucial to spotting trends
• Multi-Drug Resistance (MDR) is included in the category of emerging diseases
• Key things to learn for the exams: