Cholera

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Sari water filtration technique, designed by Rita Colwell. From: Downtoearth.org [1]
V. cholerae with flagellum. From: Uaidintl.org [2]

Etiology/Bacteriology

Taxonomy

Domain: Bacteria | Phylum: Proteobacteria | Class: Gammaproteobacteria | Family: Vibrionaceae | Order: Vibrionales | Genus: Vibrio | Species: V. cholerae

NCBI: Taxonomy Genome: Vibrio cholerae

Description

Pathogenesis

Transmission

The first recorded outbreak of cholera occurred in India in 1817, specifically near the mouth of the Ganges River [3]. Vibrio cholerae naturally attach to the chitinous exoskeleton of zooplankton in fresh, brackish rivers and coastal salt water. Because of this, cholera outbreaks often coincide with zooplankton blooms [4]. The transmission of V. cholerae is usually by water and food contaminated with zooplankton and/or fecal matter. Because the pathogen is ingested, it is also transmitted through oral-fecal transmission. The transmission of V. cholerae is often related to the inadequate sanitation and water treatment procedures of an area [5].”

Infectious dose, incubation, and colonization

V. cholerae lacks the acid resistance genes found in many other intestinal pathogens and therefore has a high infectious dose. One must ingest over one million microbes in order to contract cholera because many of the bacteria will die in the stomach due to its highly acidic environment. The incubation period is dependent upon how many organisms successfully passed through the stomach into the small intestine where V. cholerae can colonize. Therefore, the incubation period before showing symptoms ranges from a few hours to five days, typically taking two days before causing symptoms. Once in the small intestine, studies show that some of the bacteria use their flagella to swim towards the epithelial cells and adhere in the crypts of the intestine using their toxin-coregulated pilus to keep from being flushed out [6].

Epidemiology

As Cholera occurs when one comes in contact with contaminated fecal matter, outbreaks typically occur in areas with inadequate sanitation. Poorer areas without access to proper sanitation or water sources are at higher risk of infection. Cholera also becomes in issue in displacement camps, slums, and disaster zones when few sources of water are available. Water can often be contaminated with Vibrio cholerae after a natural disasters such as a flood, so cholera epidemic can be a concern during a recovery period [7].

Epidemiological studies of cholera typically focus on determining the common contaminated water source. John Snow first established this method of evaluation when studying London neighborhood water sources after an outbreak in 1854. In fact, much of what we now know about cholera came from John Snow's study on the communication of cholera [8] Often referred to as the first epidemiological study, Snow visited the infected neighborhoods, asking people about their habits, and marking infected homes on a map. From his conversations and speculation as to the transmission of the infection, Snow deduced the site of initial contamination to be a well located on Broad Street, a common water source for the infected neighborhoods. [9]

Virulence factors

The virulence factors of V. cholerae include type IV pilli, toxin co-regulated pillus, cholera toxin, and motility.

Motility

V. cholerae have flagella, which make them motile. This flagella allows the bacteria to swim through the lumen of the small intestine in search of nutrient rich cells areas and places to adhere to the epithelial cells that make up the lining of the small intestine, specifically the crypts of the small intestine. This motility could also be an important factor in the bacteria breaking through the mucosal layer that coats the inside of the small intestine [6].

Adherence

Toxin Mechanism

Clinical features

Symptoms

Morbidity and Mortality

Diagnosis

As the excrement of infection with V. cholerae is so distinct, diagnosis typically can be made upon obtaining and culturing a stool sample. Typical clinical manifestations, such as the "rice water" stool and vomiting, as well as recent consumption of a contaminated water or food source, can lead to investigation into cholera by the physician. A rectal swab or fecal sample when cultured will correctly indicate the source of the infection [10]. Cholera diarrhea is typically self-limiting, as the species is not native to human microbiota and will be expelled after several days [3].

Treatment

Prevention

Immune Response

Host Response

The human mucosal immune system is thought to act against cholera infection by the development of immunological memory to the pathogen. In studies of vaccination of humans with a strain of V. cholerae, localized and peripheral immune responses differed from initial infection, suggesting memory of the adaptive immune response induces a response to reinfection. Vaccination proved to invoke antibody responses in the intestine, as well as stimulate mucosal immunological memory. IgA antibodies were found in the highest proportion locally, suggesting IgA as the dominant isotype in intestinal tissue. In addition, in the research subjects who were not vaccinated yet were exposed a second time to V. cholerae, IFN-y secretion dramatically increased. The same was found in all but one individual in the vaccination group after a second round of vaccination, thus determining the vaccine stimulated a similar response [11].

Typically, antibody responses to infection may require large amounts of the bacteria, and the response can be short-lived. With cholera, however, the toxin is so potent that it seems to stimulate a stronger antibody response. Thus, protection from disease return in cholera can last for several years, compared to the few months associated with other infections with coproantibody stimulation [11].

Bacterial Evasion

References

1 "Stopping cholera with a sari". Down to Earth - Science and Environment Online. 2013, July 12.
2 " Kogan, Nicole. "Exploring World Involvement in Haiti". United Against Infectious Diseases. 2013, July 12.
3 Despommier D, Chen S. "Cholera". Medical Ecology. 2004.
4 News-Medical "Cholera Transmission". 2013.
5 Centers for Disease Control and Prevention (CDC). Cholera - Vibrio cholerae infection. General Information. "Where is Cholera Found". 2013, July 9.
6 Spagnuolo AM, DiRita V, Kirschner D. "A model for Vibrio cholerae colonization of the human intestine.". J Theor Biol. 2011, November 21; 289; pp. 247-258.
7 World Health Organization (WHO). Cholera - Fact sheet. 2012, July.
8 Snow, John. On the Mode of Communication of Cholera. Wilson and Ogilvy, London, 1849.
9 Summers, Judith. Soho - A History of London's Most Colourful Neighborhood, Bloomsbury, London, 1989, pp. 113-117.
10 Centers for Disease Control and Prevention (CDC). Cholera - Vibrio cholerae infection. "Diagnosis and detection". 2013, July 12.
11 The Journal of Clinical Investigation (JCI). "Intestinal immune responses in humans. Oral cholera vaccination induces strong intestinal antibody responses and interferon-gamma production and evokes local immunological memory." 1991, July. 88(1). pp. 143-148.

Created by Bhumi Patel, Dehra McGuire, and Gracen Conway, students of Tyrrell Conway at the University of Oklahoma.