Cholera

Vibrio cholerae

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Changed on: 08.04.2019
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Vibrio cholerae is a Gram-negative, motile, comma-shaped bacterium and a member of the Vibrionaceae family, which produces the so-called cholera toxin. It is categorised in different serotypes using its surface antigens (O antigen). Groups O1 and O139 (synonym: Bengal) can cause cholera outbreaks. Serotype O1 has two biotypes: classic and El Tor. The remaining serotypes – more than 200 – are referred to as non-O1/non-O139 V. cholera and could occasionally result in enteritis and various extraintestinal manifestations, such as ear or wound infections.

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Vibrio cholerae is a Gram-negative, motile, comma-shaped bacterium and a member of the Vibrionaceae family, which produces the so-called cholera toxin. It is categorised in different serotypes using its surface antigens (O antigen). Groups O1 and O139 (synonym: Bengal) can cause cholera outbreaks. Serotype O1 has two biotypes: classic and El Tor. The remaining serotypes – more than 200 – are referred to as non-O1/non-O139 V. cholera and could occasionally result in enteritis and various extraintestinal manifestations, such as ear or wound infections.

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Transmission

V. cholerae is mainly transmitted by the ingestion of drinking water or food contaminated with faeces or vomit. Given the fact that Vibrio cholera reacts very sensitively to gastric acid, the infection dose is relatively high and vehicle-dependent: 103 -106 (water) or 102 -104 (food). The dose required for infection is proportionately smaller for humans who produce less gastric acid (e.g. because of taking proton pump inhibitors).

In most cases, the agents are excreted for a few more days after the symptoms have ceased. In asymptomatic cases, the pathogens can be detected for 14 days. There have only been a few cases in which the pathogen has been excreted for several months. Direct transmission from human-to-human is rare.

Ecological niches also serve as reservoirs for V. cholerae and other species of Vibrio, in addition to the human body. Given the appropriate temperature, electrolyte and nutrient levels, Vibrio bacteria can survive in water for years. Not only can drinking contaminated water play a role in transmission, but direct contact with wounds can lead to infections, too.

Symptoms

The incubation period (time between infection and manifestation of symptoms) ranges from a few hours to five days; on average it is two to three days.

Cholera (caused by toxin producing V. cholerae O1 or O139) starts with watery diarrhoea that can be accompanied by nausea and vomiting. In serious cases, patients suffer from painless, watery diarrhoea (rice water stool) and a liquid loss of up to 20 l/day. They also suffer from severe calf cramps and increased loss of water and electrolytes. Without fluid and electrolyte substitution, this can result in kidney failure and circulatory collapse and, eventually, death. If substitution therapy is started in time, the prognosis is positive (mortality 1 %).

Asymptomatic progression or mild symptoms, which are accompanied by the excretion of the agent are very common (manifestation rate below 2 %).

In addition to gastrointestinal infections, infections with V. Cholerae non-o1/non-O139 or other Vibrio sp. could also cause infections of the ear and soft tissue and even result in sepsis and, subsequently, death in severe cases.

Therapy

The most important measure in Cholera therapy is the timely and sufficient balance of the body’s electrolyte and water levels. This can be achieved orally, if possible, with 20g glucose + 1.5g KCl + 2.5g NaCl + 3.5g Na-bicarbonate. In severe cases, IV drips must be used. Administering antibiotics to patients plays a minor role. They reduce the duration and intensity of diarrhoea in severe cases. Erythromycine, Tetracycline, Doxycycline and Ciprofloxacine are recommended antibiotics.

A therapy using antibiotics should be definitely considered for extraintestinal Vibrio infections.

Hygiene Measures

Hands must be cleaned thoroughly (washing hands with soap is sufficient!) after each visit to the toilet and before handling food (including drinking water). Moreover, all items and surfaces that have likely come/have visibly come into contact with the patient’s excrement should be disinfected.

Prevention, Immunity

An inactive, oral vaccine has been available in Austria since 2003. An oral vaccine administered twice (at an interval from 1-6 weeks) protects for about six months up to a maximum of two years. The protection level is 90%.

Patients who have suffered an infection can only expect incomplete immunity afterwards.

Non-Cholera Vibrio

Two hundred additional non-toxin producing serotypes (Vibrio cholerae non O1 and non O139) are known, in addition to the toxin-producing Vibrio cholerae strains O1 and O139. They lack the ability to produce the Cholera toxin. As a result, they are referred to as non-cholera vibrio species, to distinguish them clearly from the Cholera agents. Non-cholera vibrio species can also cause infections, although these infections are usually far less severe than a Cholera infection.

Incidence

Non-cholera vibrio species are spread around the globe and are found predominantly in water. Some species require salt -- i.e. they are found in seawater, lagoons, brackish water (mixture of saltwater and freshwater, e.g. in estuaries) in particular -- but also in landlocked lakes with increased levels of salt. They reproduce excessively at water temperatures over 20° Celsius.

Pathology 

Non-cholera vibrio species may cause diarrhoea, wound infections, middle ear infections (otitis media), the inflammation of subcutaneous tissue and, subsequently, blood poisoning. The incubation period -- i.e. the interval between infection and outbreak -- is between 12 to 24 hours. The therapy applied is based on the type of infection and would consist of antibiotic treatment, but could also require surgery and intensive medical care.

Typical risk groups, according to medical literature, are older people and individuals with weak immune systems. People with a clinical history of liver infections, diabetes mellitus, cancer/chemotherapy and severe heart conditions face a higher risk of suffering severe infections.

Incidence in Austria

Two outbreaks caused by non-cholera vibrio infections were reported in Austria in summer 2015. One of the affected patients, an 80 year-old individual with a medical history died at the end of 2015.

The increased occurrence of non-cholera vibrio in Austrian lakes could be linked to the extreme heat wave and the unusual lack of precipitation last summer. Additional tests carried out by AGES in summer 2015 found non-cholera vibrio in seven more freshwater lakes in Lower Austria and Burgenland. Migrating birds and water birds are believed to be potential sources. The levels of the classic indicator germs enterococcus and E. coli, which are used as indicators for higher levels of risk as part of the EU’s routine bathing water monitoring programme, did not increase during the examination of non-cholera vibrio species. Thus, the EU bathing waters examined conformed to all legal requirements.

The Austrian Federal Ministry of Health (BMG) has commissioned a scientific assessment at the European Centre for Disease Prevention and Control (ECDC) for this – for Austria rather new – topic.

ECDC: Monitoring programme for the Baltic Sea

Heat waves, such as the one last summer, and resulting warmer water temperatures could occur more frequently as part of global warming. This could also increase the likeliness of non-cholera vibrio in our lakes and rivers. To date, the Baltic Sea has been the only region with a potentially increased incidence.

The ECDC has put a monitoring system in place for the Baltic region, which calculates and predicts the probable occurrence of non-cholera vibrio, using the water temperature as a basis.


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