Lecture 7: Emerging and re-emerging bacterial disease Flashcards
Tuesday 28th January 2025
What is an emerging disease?
“An emerging disease is one 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.” (WHO, 2015)
What type of factors are attributed to the emergence of infectious disease?
- Human activity and habitat encroachment
- Environmental change (human drivers)
- Microbe change (human drivers)
What is a re-emerging disease?
“A re-emerging infectious disease is a disease whose incidence has increased in a defined time period and location” [after a significant period of decline].
What disease was re-emerging and on the increase up tp 2012?
Tuberculosis
What is a Multidrug-resistant (MDR) pathogen?
resistant to three or more classes of antibiotics
What is an Extensively drug-resistant (XDR) pathogen?
esistant to at least one agent in all but one or two antimicrobial classes.
What is NOT a re-emerging disease?
an outbreak or seasonal variation. e.g when there are peaks in flu cases in the winter months. A re-emerging disease has to be sustained.
Define Transmission
The mechanism in which a disease is spread i.e. faeco-oral, vector borne, etc.
Define Incubation period
The time between infection and symptom onset.
Define carrier
A person or animal without apparent disease who harbours a specific infectious agent and is capable of transmitting it to others.
Define Infectivity
The proportion of persons exposed to a causative agent who become infected by an infectious disease.
Define reservoir
The habitat in which an infectious agent normally lives, grows and multiplies; can include human reservoirs, animals reservoirs, and environmental reservoirs.
Define zoonoses
An infectious disease that is transmissible from animals to humans.
Define endemic
A disease which is constantly present in a population or geographical area.
Define Epidemic
The occurrence of more cases of disease than expected in a given area or population over a particular period of time.
Define Pandemic
Worldwide epidemic, affecting a large, widespread population simultaneously
Is lyme disease an example of an emerging infectious disease?
Yes
WHat family does lyme disease belong to ?
Spirochaetaceae
What species does lyme disease belong to?
Borrelia burgdorferi
What is the structure of the lyme disease bacteria?
spirochete (coiled, double membrane)
What is the growth of lyme disease?
microaerophilic
How is lyme disease transmitted?
vector borne transmission (black legged tick) with a zoonotic reservoir.
What are the virulence factors of lyme disease?
flagella;
motile;
exploiting immune system;
OspC lipoprotein expression.
What is the danger risk of lyme disease?
Danger: High – debilitating life-long disease.
Describe the pathogenesis of lyme disease
- Erythema Migrans (EM) rash
- Arthritis
- Facial palsy
- Radiculoneuropathy
- Meningitis
- Carditis
Is it true that B. burgdorferi enters vertebrate host epithelium & migrates into tissue & joints ?
Yes
How does B. burgdorferi attach to the tick?
By expressing Outer surface Protein A (OspA)
Describe the 3 host tick cycle of lyme disease
Check facts!
- Tick’s go through Malt stages and as they grow, they change the type of animals that they feed on.
- When they’e adults, they continue to feed on larger vertebrates and lay eggs that will last over the winter.
- They will then feed on smaller vertebrates, who will pick up the infection again.
Is it hard to remove the lyme ticks once bitten?
Yes, as they bite and then remain stuck in place in situ
Is there a human vaccine for lyme disease?
No
How can people reduce their exposure to tick bites?
- Personal protection
- deer and land management
- acaricides
- education
What can lyme disease be treated with if caught early?
doxycycline
At wha ttime of the year are there the most cases of lyme disease?
The summer, when people typically go on long tick-infested walks
What type of people are at a higher risk of contracting lyme disease?
The young, the elderly, men
Are TB and HIV co-infections?
Yes, and they’re prevalence has been increasing simultaneously
What is the causative agent of cholera?
Vibrio cholerae O1 or O139 toxigenic strains.
What are the characteristics of cholera?
Gram negative, facultative anaerobe, comma shaped rod, flagellated.
How is cholera transmitted?
faeco-oral from contaminated water (or food).
What are the virulence factors of cholera?
cholera enterotoxin; adherence factors (Hemagglutinins)
What is the danger of cholera?
Danger: Very high – highly contagious, extreme dehydration within hours if untreated.
is cholera an emerging or a re-emerging disease?
Re-emerging
How does the cholera endotoxin cause sudden and dramatic ‘rice water’ diarrhoea?
- 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
What results in death from cholera?
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.
Is it true that cholera is endemic in many countries?
Yes
How many global pandemics did cholera lead to?
Led to 6 global pandemics, killing millions.
How many cases of cholera are there annually worldwide?
1.3-4.0 million cases annually worldwide (but only 140,000 reported).
What can high cholera cases in a particular area be an indicator of?
Can be an indicator of lack of socio-eco development and sanitation.
What is the reemergence of cholera linked to ?
Re-emergence linked to increasing size of vulnerable populations living in unsanitary conditions (Displaced persons
; Infrastructure breakdown
)
What can help to prevent cholera?
Safe water and sanitation, and the cholera vaccine
What can be used to treat cholera once it’s contracted?
- Rehydration therapy (Oral or intravenous; salts and mineral replacement).
- Antibiotic treatment
- Zinc treatment
-
Are surveillance and rapid responses to outbreaks required to prevent the mass transmission of cholera?
Yes
Does the world health organisation give out cholera outbreak response kits?
Yes
Describe the Haiti cholera epidemic of 2010
- Case fatality rate = ~5%, which is high for a preventable and treatable disease.
- Had an earthquake and response team from Nepal spread cholera to Haiti.
- Impacts of the disease weer worsened by the fact that the earthquake had disrupted and weakened the healthcare system.
Is shigella an emerging or reemerging disease?
Shigella is a re-emerging disease
What family does shigella come from?
Family: Enterobacteriaceae
What are the characteristics of shigella?
Gram negative, facultative anaerobe, non-motile.
How can shigella be transmitted?
faeco-oral, (sexually transmitted).
What are the virulence factors of shigella?
invasion of epithelial cells, shiga (vero) toxin production.
What is the danger level of shigella?
Danger: Moderate – self limiting infection in most cases, life threatening for vulnerable (young, old, immunocompromised).
Is shigella an invasive intestinal infection that induces a mass inflammatory response ?
Yes
What types of inflammatory responses are induced by shigella?
watery or bloody diarrhoea
What type of person does shigella mostly target?
Children
How many deaths does shigella cause annually?
Causes 200,000 deaths annually.
Shigella may be caused by any of the 4 Shigella species, which are….
S. dysenteriae, S. boydii, S. sonnei and S. flexneri.
Why is shigella difficult to treat with antibiotics?
Because all the species are highly multi-drug resistant, most recently to ciprofloxacin
