Cholera: The Peculiarities Of Infectious Disease

Cholera is a disease characterized by extreme bouts of diarrhea (Somboonwit, Menezes, Holt, Sinnott, and Shapshak, 2017). In the 19th century, Cholera was believed to be a disease caused by breathing “bad air”, however researcher John Snow showed that cases of the disease were clustered around a public well (Symington, 2016). Upon inspecting the water from the well, John Snow discovered the presence of white particles floating giving weight to his theory that the disease was caused by waterborne bacterium (Symington, 2016). We now know the disease is caused by Vibrio cholerae, a gram-negative bacterium (Harris, LaRocque, Qadri, Ryan, and Calderwood, 2012). Under microscope the bacterium appears as a comma with a single flagellum for propulsion (Somboonwit et. al., 2017). Though there are hundreds of V. cholerae serogroups, only two, O1 and O139 serogroups, cause disease in humans (Harris et. al., 2012).

Prevalence

In the updated report by Ali, Nelson, Lopez, and Sack (2015), countries in Africa and southern Asia have the highest incidence rates of Cholera. Since Cholera is highly under reported due to a variety of factors such as social, economic and environmental circumstances, the exact numbers for incidence and case fatality rates are unknown (Ali et. al., 2015). However, current estimates put 1.4 billion people at risk of Cholera, and 2.9 million of those at-risk populations develop the disease (Ali, Nelson, Lopez, and Sack, 2015). Previously, the World Health Organization reported that the case fatality rates ranged from 0.0% to 15.8% in 2016 (Cholera case fatality rate, 2017). Since then, the World Health Organization (2017) reported that the case fatality rate is typically below 1% as reported by the most impacted countries. Children are the most vulnerable and comprise an estimated 50% of all Cholera cases and deaths (World Health Organization, 2017).

Chain of infection

V. cholerae’s natural reservoir is typically slightly salty waters (Almagro-Moreno and Taylor, 2013). V. cholerae is greatly affected by environmental factors like temperature, salt, pH and available nutrients (Almagro-Moreno and Taylor, 2013). In fact, V. cholerae experience optimal growth in waters with 0.2-3% salinity, 30-40ºC and with a pH of 8 (Vezzulli, Pruzzo, Huq, and Colwell, 2009). Within and around aquatic environments, fish, bivalves, lake flies and birds are some of the known hosts of Cholerae (Vezzulli et. al, 2009).

The route of transmission of Cholera is the faecal-oral route (World Health Organization, 2017). Humans are a natural host of V. cholerae and can contract the bacterium by consuming water or food that has been contaminated (Somboonwit et. al., 2017). Although the infectious dose needed to cause disease in humans is high (, it may be lowered if an individual’s stomach acid is altered (Hussain, Fazil, and Singh, 2011). If enough bacteria survive and pass from the stomach, they then begin to colonize the small intestine (Nelson, Harris, Morris, Calderwood and Camilli, 2009). Once in the small intestine, V. cholerae have two main virulence factors; 1) cholera toxin and 2) toxin-coregulated pilus (Nelson et. al., 2009). Cholera toxin is the substance responsible for the diseases staple characteristic secretory diarrhea (Wernick, Chinnapen, Cho, and Lencer, 2010). The toxin-coregulated pilus allow the V. cholerae cells to bind together and hold a position in the intestinal lumen (Nelson et. al., 2009). V. cholerae has an incubation period ranging between 2 hours to 5 days (Somboonwit et. al., 2017). According to Somboonwit et. al. (2017) most Cholera hosts are asymptomatic. However, asymptomatic hosts still shed high numbers of the bacteria through feces contributing further contamination (Nelson et. al., 2009).

As noted previously, the mainstay symptom of Cholera is secretory diarrhea (Somboonwit et. al., 2017). The diarrhea can be described as similar to that of rice water, with a pungent, fishy smell (Somboonwit et. al., 2017). If left untreated, symptomatic individuals may succumb to dehydration as fluid loss has been known to be as much as one litre every hour (Hussain et. al., 2011). Patients experiencing dehydration may be lethargic, have a fast but weak pulse and altered skin turgor as demonstrated by a pinch test (Somboonwit et. al., 2017). Further, symptoms resulting from loss of electrolytes may manifest as muscle weakness, fatigue, cramps and confusion (Somboonwit et. al., 2017).

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Currently the test for cholera is to sample faecal contents of those suspected to be infected by the bacteria (World Health Organization, 2017). However, this method of testing is time-consuming and expensive, requiring the samples to be transported to laboratories with equipment necessary for testing as well as trained individuals to operate (World Health Organization, 2017). Polymerase chain reaction tests are also available providing a more accurate result, however they also require lab facilities and equipment (World Health Organization, 2017). Perhaps more preferably, rapid diagnostic tests can be performed in the field allowing for quick diagnosis and do not need to be performed by someone with extensive training (World Health Organization, 2017).

Rehydration therapy is the primary treatment of symptomatic cholera reducing the fatality rate significantly (Harris et. al., 2012). Antibiotic medications are available but are only an adjunct to rehydration therapy and to increase recovery rate (World Health Organization, 2017).

Community Context – Small Cities and Towns in Africa

Cholera is most prevalent in developing countries and effects the poorest of the population (World Health Organization, 2017). Many of the social determinants of health contribute to the persistence of the disease such as income and social status; social support networks, education, physical environment and personal health practices, just to name a few (Olago, Marshall, and Wandiga, 2007). The rest of this paper will focus on the impact of economic stability and environment as well as discuss methods of prevention.

The most effected by Cholera are the poorest in developing countries (Olago et. al., 2007). The majority of individuals effected are living on little income due to being self-employed, or being farmers who primarily eat what they grow (Olago et. al., 2007). In these areas government medical support can be scarce, and as such the private sector has become a large contributor of medical supplies, increasing the gap for low income individuals (Olago et. al., 2007). It is also difficult for individuals to protect themselves even through one of the simplest ways, boiling water; this is due to the price of wood being a common concern, as wood is required to start a fire to then boil the water (Olago et. al., 2007). Economics is not just an individual or community issue as Cholera outbreaks put a financial strain on governments as well (Olago et. al., 2007). However, Non-Government Organizations have been available to help communities set up methods of prevention like digging wells and building latrines (Olago et. al., 2007).

Cholera outbreaks have been tightly associated with climate, meaning that the environment one lives in is an important factor (Olago et. al., 2007); for example, Cholera outbreaks have been strongly associated with rainfall and temperature (Rebaudet, Sudre, Faucher, and Piarroux, 2013).

Disease Prevention and Management

Prevention of Cholera can be increased by improving access to clean water, building latrines in safe locations to eliminate the risk of further contamination, and educating the public on proper hygiene (World Health Organization, 2017; Rebaudet et. al., 2013; Somboonwit et. al., 2017). At the local level, increasing the access to clean water and creating ways to clean water is a simple prevention method that could be implemented; for example, the use of seri cloths to filter water has been shown to reduce Cholera infection (Almagro-Moreno and Taylor, 2013). However, more effective household water treatments are available, such as liquid chlorine and chlorine tablets, solar radiation, and boiling (Lantagne, and Yates, 2018). The Global Task Force on Cholera Control is also committing to prevent the disease by increasing surveillance and decreasing response time to implement support (Somboonwit et. al., 2017).

References

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