Module 1: Answers to Activity Questions

Answers to Questions in Module 1.1

Here are the answers to the questions in Module 1.1:

  1. There is a lot of under-reporting of cholera cases (Ali et al 2015, Hegde et al 2024). In the MSF video, they say it is estimated that only 5-10% of cholera cases are reported to the WHO each year.

  2. The MSF video says that in endemic areas, healthy carriers far exceed the percent of people who show symptoms (upon infection with the current pandemic lineage of V. cholerae, ie. the 7PET lineage). That it, it is estimated that most people who are infected with the 7PET lineage are asymptomatic (Nelson et al 2009). The percent of people who develop symptoms (e.g. acute watery diarrhoea) probably varies a lot between populations, as populations that have suffered recent outbreaks caused by 7PET likely have greater immunity (Bencić & Sinha 1972, Nelson et al 2009). Asymptomatic carriage is likely responsible for considerable regional and global transmission of the 7PET lineage (King et al 2008, Islam et al 2017).

  3. The video by the IAQ video Network says that there have been outbreaks of diarrhoeal illness caused by eating shellfish (containing non-epidemic V. cholerae) from the Gulf of Mexico region of the USA. For example, Haley et al 2014 described a small outbreak of 11 cases of diarrhoeal illness caused by consumption of oysters (containing non-epidemic V. cholerae) from the Gulf of Mexico region of the USA. Several different lineages of non-epidemic V. cholerae have been identified in the coastal waters of the Gulf of Mexico; one of these lineages was even named ‘Gulf Coast’ because it was first isolated from the Gulf of Mexico (see Figure 6 in Module 1.1; Kaper et al 1982, Domman et al 2017).

  4. The length of protection after infection with cholera is a subject of ongoing scientific research; it may depend on the severity of the previous infection, and on how similar the V. cholerae causing new infection is to the V. cholerae that caused the previous infection in its genes for key antigens (Leung & Matrajt 2021, Harris 2018). In the interview with Dr Qadri, she says that a person who suffers from severe cholera is protected from reinfection for approximately 7-10 years. Harris 2018 says there is strongest evidence for protection for the first 3 years after a cholera infection, and that the length of protection may depend on whether the V. cholerae causing new infection is the same or different in its genes for key antigens compared to the V. cholerae that caused the previous infection.

  5. In the interview with Dr Qadri, she says that the current oral cholera vaccines are 60-70% efficacious.

Answers to Questions in Module 1.2

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Answers to Questions in Module 1.3

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Answers to Questions in Module 1.4

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Vibriowatch

In later modules of this course, you will learn how to carry out bioinformatics analyses using Vibriowatch, as well as other bioinformatics tools. If you already have cholera genomic data to analyse, and want to get going quickly, you may also be interested in our Vibriowatch tutorial.

Contact

I will be grateful if you will send me (Avril Coghlan) corrections or suggestions for improvements to my email address alc@sanger.ac.uk

Acknowledgements

Contributors to this course: Avril Coghlan, Matt Dorman, Ismail Bashir, Anne Bishop, Amber Barton, Stephanie McGimpsey, Jolynne Mokaya, Nisha Singh, Nick Thomson.