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Source: Health Canada

 Know before you go!
Infectious diseases not necessarily common in Canada can occur and may even be widespread in other countries. Standards of hygiene and medical care may differ from those at home. Before departure, you should learn about the health conditions in the country or countries you plan to visit, your own risk of disease and the steps you can take to prevent illness.

The risk is yours
Your risk of acquiring a disease depends on several factors. They include your age, gender, immunization status and current state of health; your itinerary, duration and style of travel (e.g., first class, adventure) and anticipated travel activities (e.g., animal contact, exposure to fresh water, sexual contact); as well as the local disease situation.

Risk assessment consultation
Health Canada strongly recommends that your travel plans include contacting a travel medicine clinic or physician 6 to 8 weeks before departure. Based on your individual risk assessment, a health care professional can determine your need for immunizations and/or preventive medication (prophylaxis) and advise you on precautions to avoid disease. We can help you locate a travel medicine clinic closest to your home.

Some facts from the experts
The information below has been developed and is updated in consultation with Health Canada's Committee to Advise on Tropical Medicine and Travel (CATMAT). The recommendations are intended as general advice about the prevention of cholera for Canadians travelling internationally.

Disease profile
Cholera is an acute intestinal infection caused by the bacterium Vibrio cholerae. The bacteria produces a toxin that causes an infected person to dehydrate through vomiting and profuse watery diarrhea. Two strains of cholera are now associated with infection: V. cholerae serogroup O1 and V. cholerae serogroup O139.

Cholera infection is associated with poor sanitation, often due to inadequate sewage and water treatment facilities in non-industrial countries. Infection is generally acquired from contaminated water or food, particularly undercooked or raw shellfish and fish.

Transmission
Cholera is acquired directly through contaminated water or food, or indirectly from exposure to the feces or vomit of an infected person. Indirect exposure, or person-to-person exposure, is unlikely when good hygiene practices (e.g., hand washing) are in place. Undercooked or raw shellfish, such as crabs, fish, shrimp, mussels and oysters, and unpeeled fruits and vegetables have been associated with infection. Cholera outbreaks are usually caused by contaminated water, where sewage and drinking water supplies have not been adequately treated.

Geographic distribution and incidence trends
Cholera is found in many tropical countries around the world where outbreaks are common. New outbreaks can occur sporadically in any part of the world where water supplies, sanitation, food safety and hygiene are inadequate. The greatest risk of cholera occurs in overpopulated communities and refugee settings characterized by poor sanitation and unsafe drinking water. Historically until 1992, only serogroup O1 caused epidemic cholera.

V. cholera O1 caused epidemic cholera in South-East Asia in the 1960s. It then appeared in West Africa in the 1970s, where it had not occurred previously for over 100 years. The disease is now endemic to most of Africa. In 1991, cholera struck Latin America, after an absence of more than a century. Within one year, it had spread to 11 countries and, subsequently, throughout the continent.

In 1992, a new serogroup (V. cholera O139) was identified during a large outbreak of cholera in India and Bangladesh. Since then, 11 countries in South-East Asia have reported V. cholera O139 cases.

For more details on countries reporting cholera cases, see Table 1: Reported Cholera Activity, by Area & Country, 1999.

Cholera in Latin America

Many countries in the Region of Americas are experiencing unexpected outbreaks of cholera associated with extreme weather conditions brought by the arrival of the El Niño phenomenon. During 1998, the following countries have already reported cholera outbreaks: Bolivia (mainly in La Paz Department) 165 cases and 5 deaths; Honduras (La Mosquitia, Gracias a Dios Department) 280 cases and 13 deaths; Ecuador (mainly in Loja Province) 76 cases and 1 death; Peru (various departments) 16,705 cases and 146 deaths; Nicaragua (border area with Honduras) 336 cases and 16 deaths. It is expected that other countries in the Region will report increased cholera incidence in the coming months.

Preventive and control measures are being taken by the ministries of health of the affected countries. However, as the epidemic in Latin America enters its eighth year and with the added impact of E1 Niño, cholera will continue to challenge governments and health agencies; additional international resources for emergency preparedness and control measures will be needed this year. WHO/PAHO is working closely with countries in the Region to reactivate cholera preparedness and response plans.

Source: WHO Weekly Epidemological Record, Vol 73, No 15, 1998.

Symptoms
The incubation period for cholera ranges from less than 1 day to 5 days. Most persons infected with cholera do not become ill, although the bacterium is present in their feces for 7-14 days. When illness does occur, infection causes only mild or moderate diarrhea in roughly 90% of individuals. In 5-10% of cases, infected individuals develop severe, watery diarrhea and vomiting. The resulting loss of fluids in an infected individual can rapidly lead to severe dehydration. If not treated, death can occur within hours.

Treatment
The most important treatment is rehydration, which consists of prompt replacement of water and salts lost through diarrhea and vomiting. Patients who have become severely dehydrated may be given intravenous fluids, while oral rehydration with glucose-electrolyte solutions may be adequate for mild cases. In serious cases, an effective antibiotic can be used to reduce diarrhea.

Prevention and personal precautions
Most travellers visiting an area where cholera occurs are at very low risk of acquiring infection. The estimated risk of cholera in European or North American travellers to endemic areas is 1 or 2 cases per 1 million trips. Taking food and water precautions (see recommendations below) is the best means of preventing cholera infection.

Vaccination
An oral, live, attenuated cholera vaccine - CVD 103-HgR (Mutachol®) - is licenced in Canada and is partially effective against cholera; that is, against serogroup O1 only. The vaccine is administered as a single dose and is approved for adults and children over 2 years of age.

Vaccination is not recommended for the prevention of cholera in the majority of travellers to endemic areas for the following reasons:

• the risk of acquiring cholera for travellers is generally low;
• vaccine efficacy, while very good for serogroup O1, affords no protection against serogroup O139, which is currently found in 11 countries in South-East Asia;
• the vaccine is of a relative high cost given the low risk of cholera infection.

However, travellers who may be at increased risk for acquiring cholera --for example, health professionals working in endemic areas, aid workers in refugee camps, travellers to remote cholera areas without access to safe water supplies -- may wish to consider receiving the vaccine. Travellers should seek a detailed, individual risk assessment to determine their need for vaccination.

Safety

Randomized controlled studies have been carried out in several thousand subjects in a number of cholera-endemic and non-endemic areas, and have demonstrated good safety of the vaccine^(1-5).

Immunogenicity

Several studies have shown a good immune response with seroconversion rates > 90% following a single oral dose of the vaccine^(1-7). Seroconversion occurred as early as 8 days after administration of the vaccine and lasted for 6 months.  

Protective efficacy of the vaccine was tested in volunteers challenged with pathogenic V. cholerae of both biotypes and serotypes. Complete protection against the classical biotype was demonstrated in 82% to 100% of subjects, and in 62% to 67% of subjects exposed to the El Tor biotype. However, even when the vaccine did not provide complete protection, no volunteer lost > 1 L diarrheal fluid/24 hours.

No cholera vaccine currently available has been shown to be protective against the O139 Bengal strain that emerged in south Asia starting in 1992.

Adverse reactions

The side-effect profile for the vaccine group was similar to the control (placebo) group. Adverse reactions were mild in nature and of short duration. They included nausea, abdominal cramps, and diarrhea^(1-5).

Booster dose

An optimal booster dose or interval has not yet been established⁽⁷⁾. However, the manufacturer recommends that a repeat dose be given every 6 months if indicated.

Recommendations
Because cholera is spread through contaminated food and water, Health Canada strongly recommends that travellers exercise general food and water precautions to minimize their risk of exposure. The key principles to remember are: boil it, cook it, peel it or leave it!

• Eat only food that has been well-cooked and is still hot when served.
• Drink only purified water that has been boiled or disinfected with chlorine or iodine, or commercially bottled water in sealed containers.
• Drinking carbonated drinks without ice, including beer, is usually safe.
• Avoid ice, unless it has been made with purified water.
• Boil unpasteurized milk.
• Avoid unpasteurized dairy products and ice cream.
• Avoid uncooked foods -- especially shellfish -- and salads. Fruit and vegetables that can be peeled are usually safe.
• Avoid food from street vendors.
• Wash hands before eating or drinking.

Health Canada does not recommend the use of antibiotics as a preventive measure. However, following an individual risk assessment, antibiotics may be prescribed by a physician for use should diarrhea develop.

Some things to think about...
By taking a few food and water precautions and emphasizing personal hygiene while travelling, you can protect yourself against cholera. Remember: boil it, cook it, peel it, or forget it!

If you should develop nausea, stomach cramps, diarrhea or vomiting during travel to a cholera-endemic area or after returning, seek medical attention and report your recent travel history.

For more information...

• For more information on cholera worldwide, visit the World Health Organization's Communicable Disease Surveillance and Response page on cholera at: http://www.who.int/emc/diseases/cholera/
• For more Know before you go! information, click here.

• For travel medicine professionals, visit the Committee to Advise on Tropical Medicine and Travel (CATMAT) "Statement on Oral Cholera Vaccination".

Source: Weekly Epidemiological Record (WER), No. 31 (4 August, 2000), World Health Organization

WHO Weekly Epidemological Record, Vol 73, No 15, 1998. 

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