Vibrio cholerae

Causes cholera, a severe diarrheal illness that is transmitted with the fecal-oral route (food or water), and specifically associated with improper sanitation

Microbiology

Curved, motile Gram-negative bacillus
Serogroups O1 and O139 cause epidemic cholera, others cause mild gastroenteritis

Can grow in salt water with organic material
Human are only known hosts
Ingestion of contaminated water leads to small intestine colonization mediated by TCP (toxin coregulated pili)
- Vibrio is non-invasive
Severe secratory diarrhea cause by cholera toxin (CT)
- CT causes severe secretory diarrhea
- It enters epithelial cells by binding to a glycosphingolipid, GM1
- Inside the cell, it increases activity of adenylyl cyclase, causing an increase in cAMP, which causes chloride ion secretion
- CT is encoded by ctxAB genes, which were added to TCP-positive V. cholera by a bacteriophage

3-5 million people affected annually
100-120,000 deaths annually, but likely underestimated
Typically in poor countries with poor sanitation
Seven pandemics described since 1817
- The seventh and current pandemic started in Indonesia in 1961, and is currently still circulating
  - The current strain is called El Tor

6h to 5d onset requiring very low innoculum
Profuse painless watery diarrhea with rice-water stools
- Up to 1 L/h
Abdo cramping and nausea
Only rarely associated with fever, as it is non-invasive
- More likely to be hypothermic from severe dehydration

Severe, life threatening dehydration occurs in 10-20%
- Profuse diarrhea, leading to shock from profound fluid losses, and, eventually, death
Signs are those of severe dehydration:
- Lethargy or loss of consciousness
- Sunken eyes
- Low skin turgor
- Low blood pressure and weak pulse
- Unable to drink

90% of colonized patients are asymptomatic but still infectious [CITATION NEEDED]
Among those who are symptomatic, they can shed it for months after illness (though most stop 2-3 days after symptom resolution)

Usually clinical diagnosis in low-resource settings
Stool culture
- Helpful for determining resistance during outbreaks, but not routinely done
Rapid stool tests, requiring dark field microscopy to see "shooting star" appearance of vibrios
Serology, sometimes

Isolation
Rehydration is the main way to reduce mortality
- Mild: alert with normal exam
  - Oral rehydration at home, guided by thirst
  - Should be observed until they are reliably replacing their losses, then can be discharged home
- Moderate: alert to restless, with some abnormalities on exam to suggest dehydration
  - Oral or IV rehydration in hospital
  - Bolus 75 mL/kg over 3-4 hours
  - Replace losses
  - Observe until signs of dehydration resolves and patient peeing
- Severe: cholera gravis, as described above
  - Aggressive IV rehydration in hospital
  - Bolus >100 mL/kg as rapidly as possible until circulation is restored, then the remainder over 3 hours
  - Replace losses
Replace electrolytes as needed, but laboratory assistance is not required in most cases
Antibiotics decrease duration and volume of diarrhea, and are indicated in cases of moderate or severe cholera
- Doxycycline 300 mg po once, avoided in pregnant women and children <8 years
- Azithromycin 1 g po once
- Ciprofloxcin used previously, but increasing resistance
Avoid antiemetics and antimotility agents
Consider zinc supplementation in children 10-30 mg daily x5-7 days
Can use a cholera cot

D5/lactated Ringer's (D5LR) is the preferred IV fluid, though D5-NS can be used if D5LR is not available
- "Dhaka solution" has more potassium, bicarbonate, and glucose, and is optimal
NS can be used for circulatory support
Oral rehydration solutions (ORS) have salt and glucose
- In an emergency, can add 1/2 tsp salt with 6 tsp sugar in 1 L of clean water

Dukoral and Shanchol are both killed Vibrio vaccines
Immunity lasts 6 months to a few years, not approved in children
- Boosters every 2 years
Both vaccines are well-tolerated but only 60-80% effective
During outbreaks, they have about 80% effectiveness