What is Cholera? How to Use the Cholera Rapid Test Kit?
Despite being largely predictable and preventable, cholera remains an important global threat to public health. Since its initial transmission from its original reservoir in the Ganges delta during the 19th century, cholera has caused six subsequent pandemics that have killed millions of people across all continents. The seventh cholera pandemic started in South Asia in 1961, spread to Africa in 1971, reached the Americas in 1991, and retains an epidemic or endemic presence in many countries to this day. Today, cholera remains a major indicator of inequality in access to the bare necessities required for human well-being. However, the development of an effective cholera vaccine and rapid point-of-care test kits may assist in the mitigation of the burden of cholera in cholera-endemic countries and in areas at risk for cholera outbreaks. Read along to learn more about cholera, its epidemiology, and its symptoms, along with the Cholera Rapid Test Kit is used to assist in its detection.
What causes Cholera?
Cholera is an acute diarrheal illness caused by infection of the small intestine with toxigenic bacteria of the species Vibrio cholerae. Vibrio cholerae is a species of gram-negative, highly mobile, facultative anaerobe bacteria with a comma-like shape. Two serogroups of Vibrio cholerae, O1, and O139, are responsible for cholera outbreaks in human populations. Since the bacteria naturally inhabit brackish or saltwater sources and often attach themselves to the shells of different shellfish species, cholera spreads primarily through the fecal-oral route as a result of the consumption of contaminated water or undercooked seafood. However, human-to-human transmission of the infection can also occur through direct contact with contaminated human feces.
Once it enters the host body, Vibrio cholerae invades the intestinal mucosa and colonizes the small intestine with the help of cholera toxin (CT) and the toxin coregulated pilus (TCP). Cholera toxin (CT) is a protein that enables the attachment of bacteria to the intestinal epithelial cells of the host. On the other hand, the toxin coregulated pilus (TCP) is a long, thin, flexible, filamentous component on the surface of bacterial cells that assists with intestinal colonization. Together, the cholera toxin (CT) and the toxin coregulated pilus (TCP) are decisive for the activity and pathogenicity of Vibrio cholerae.
How common is Cholera?
According to the World Health Organization (WHO), an overall number of 323,369 cholera cases and 857 deaths were reported from 24 countries in 2020. However, the actual burden of cholera is estimated to be much higher given the prevalence of asymptomatic cases, limitations in surveillance systems, and fear of the impact on trade or tourism. In fact, the agency estimates that cholera affects 1.3 to 4.0 million people worldwide, with 21 thousand to 143 thousand of deaths each year. Today, cholera disproportionately affects regions with poor sanitation, crowding, war, and famine across Asia, Africa, Latin America, India, and the Middle East. Especially areas with inadequate water treatment, poor sanitation, inadequate hygiene, limited safe water or nutrition resources, and lack of access to healthcare are at higher risk for the emergence and circulation of cholera.
What are the symptoms of Cholera?
Although the estimations of the ratio of asymptomatic to symptomatic infections demonstrate significant variance, many people infected with cholera may not experience any symptoms. However, asymptomatic individuals can still shed the bacteria back into the environment through their feces and infect other people. The majority of symptomatic individuals present with mild to moderate symptoms that may develop suddenly within 12 hours to 5 days following the initial ingestion of contaminated water or food. The most common symptom of cholera is profuse watery diarrhea or vomiting of clear fluid. The diarrhea is often described to resemble “rice water” and may have a fishy odor. In a minority of infected cases, severe acute watery diarrhea may lead to severe dehydration and electrolyte imbalance, which may lead to the death of the patient in a few hours if left untreated. While fever is rare, patients may experience secondary symptoms such as lethargy, sunken eyes, dry mouth, cold or clammy skin, wrinkled hands or feet, labored breathing, blood pressure drops, rapid peripheral blood pressure, rapid peripheral pulse, and decreased urine output. Particularly in children, the infection may also lead to muscle cramps, muscle weakness, impaired consciousness, seizures, or coma. Severe dehydration may also cause the patients’ skin to turn bluish-gray in color, leading to cholera being named “the blue death.” Although antibiotic treatment and supportive therapy are highly effective for the prevention of death, severe cases of cholera are estimated to kill around 50% of the affected patients without medical intervention.
How To Use the Cholera Rapid Test Kit?
Since many different pathogens may cause acute watery diarrhea, diagnosing a patient with cholera is almost impossible based solely on clinical presentation. Thus, stool culture and rapid diagnostic testing (RDT) are essential for the confirmation of cholera in patients upon clinical suspicion. Although laboratory testing based on the culture of stool specimens remains the gold standard for the diagnosis of cholera and the identification of the responsible serogroups, rapid antigen tests (RDTs) are recommended in cholera-epidemic regions and in the case of outbreaks to strengthen disease surveillance, improve national preparedness, enhance accessibility, and facilitate immediate intervention.
Rapid test kits for detecting cholera are lateral flow immunochromatographic assays intended to detect antigens unique to the O1 and O139 serogroups of Vibrio cholerae in solid, semisolid, viscous, or liquid stool specimens. These kits typically include swabs for the collection of solid specimens and disposable droppers for the collection of liquid specimens. Following the collection of the stool specimen with the specified tool, the collected specimen is mixed thoroughly with the extraction buffer to ensure its transfer from the swab or dropper to the solution in the extraction tube. Next, the test cassette is removed from its foil pouch and placed on a flat surface. Then, a few drops of the solution containing the processed sample is added to the assigned well on the test cassette, and a timer is started. The test kit provides qualitative results indicated by the appearance of the test line (T) and incorporates internal controls confirmed by the appearance of the control line (C) on the test cassette. In order to ensure their validity, the results should be read within the period specified in the instructions manual.
REFERENCES
Weil, A. A., & LaRocque, R. C. (2020). Cholera and Other Vibrios. Elsevier EBooks, 486–491. https://doi.org/10.1016/b978-0-323-55512-8.00047-8
