Cholera And Other Vibrios

VIBRIO CHOLERAE(SEROGROUPS O1 AND O139)

Identification• An acute bacterial enteric disease characterized in its severe form by

sudden onset, profuse painless watery stools (rice-water stool), nausea and profuse vomiting early in the course of illness. In untreated cases, rapid dehydration, acidosis, circulatory collapse, hypoglycaemia in children, and renal failure can rapidly lead to death.

• In severe dehydrated cases , death may occur within a few hours, and the case-fatality rate may exceed 50%.

• With proper and timely rehydration, this can be less than 1%.

Diagnosis • is confirmed by isolating Vibrio cholerae of the serogroup O1

or O139 from feces.

• V. cholerae grows well on standard culture media, the most widely used of which is TCBS agar.

• The strains are further characterized by O1 and O139 specific antisera.

• If laboratory facilities are not nearby or immediately available, Cary Blair transport medium can be used to transport or store a fecal or rectal swab

• For epidemiological purposes, a one-step dipstick test for rapid detection of V. cholerae O1 and O139 has been developed and should soon be available on the market to improve application of effective public health interventions.

• In epidemics, once laboratory confirmation and antibiotic sensitivity have been established, it becomes unnecessary to confirm all subsequent cases. Shift should be made to using primarily the clinical case definition proposed by WHO as follows:

• Disease unknown in area: severe dehydration or death from acute watery diarrhea in a patient aged 5 or more

• Endemic cholera: acute watery diarrhea with or without vomiting in a patient aged 5 or more

• Epidemic cholera: acute watery diarrhea with or without vomiting in any patient.

Infectious agent• Only Vibrio cholerae serogroups O1 and O139 are associated

with the epidemiological characteristics and clinical picture of cholera.

• Serogroup O1 occurs as two biotypes– classical and El Tor.

• each of which occurs as 3 serotypes (Inaba, Ogawa and rarely Hikojima).

• In any single epidemic, one particular serogroup and biotype tends to be dominant

Occurrence

• Cholera is one of the oldest and best understood epidemic diseases.

• Epidemics and pandemics are strongly linked to the consumption of unsafe water, poor hygiene, poor sanitation and crowded living conditions.

• Man-made or natural disasters such as complex emergencies and floods resulting in population movements as well as overcrowded refugee camps are conducive to explosive outbreaks with high case fatality rates.

ReservoirThe main reservoir is humans.

Incubation periodFrom a few hours to 5 days, usually 23 days.

Mode of transmission• Cholera is acquired through ingestion of an infective dose

of contaminated food or water and can be transmitted through many mechanisms.

• Water usually is contaminated by feces of infected individuals and can itself contaminate, directly or through the contamination of food.

• Outbreaks or epidemics as well as sporadic cases are often attributed to raw or undercooked seafood.

Period of communicability

• As long as stools are positive, usually only a few days after recovery.

• Occasionally the carrier state may persist for several months.

Susceptibility

• Variable; gastric achlorhydria increases the risk of illness, and breastfed infants are protected.

• Cholera occurs significantly more often among persons with blood group O.

• Infection with either V. cholerae O1 or O139 results in a rise in agglutinating and antitoxic antibodies, and increased resistance to reinfection.

VIBRIO CHOLERAESEROGROUPS OTHER THAN

O1 AND O139• Organisms of V. cholerae serogroups other than O1 and O139

have been associated with sporadic cases of foodborne outbreaks of gastroenteritis, but have not spread in epidemic form.

• They have been associated with wound infection and also, rarely, isolated from patients (usually immunocompromised hosts) with septicemic disease.

• Non-O1/non-O139 V. cholerae strains are associated• with 2%–3% of cases (including travellers) of diarrheal illness

in tropical developing countries.

VIBRIO PARAHAEMOLYTICUSENTERITIS

• An intestinal disorder characterized by watery diarrhoea and abdominal cramps in nearly all cases, usually with nausea, vomiting, fever and headache.

• About one quarter of patients experience a dysentery-like illness with bloody or mucoid stools, high fever and high WBC count.

• Typically, it is a disease of moderate severity lasting 1–7 days; systemic infection and death rarely occur.

• Diagnosis is confirmed by isolating Vibrio parahaemolyticus from the patient’s stool on appropriate media (typically TCBS media).

• or identifying 105 or more organisms per gram of an epidemiologically incriminated food (usually seafood).

Methods of control

Preventive measures• Traditional injectable cholera vaccines based on killed

whole cell microorganisms provide only partial protection (50% efficacy) of short duration (3–6 months) they do not prevent asymptomatic infection and are associated with adverse effects. Their use has never been recommended by WHO.

Control of patient, contacts and the immediate environment

• Isolation: Hospitalization with enteric precautions is desirable for severely ill patients; strict isolation is not necessary.Less severe cases can be managed on an outpatient basis with oral rehydration and an appropriate antimicrobial agent to prevent spread.

• Concurrent disinfection: Of feces and vomit and of linens and articles used by patients, using heat and disinfectant.

• Management of contacts: Surveillance of persons who shared food and drink with a cholera patient for 5 days from last exposure

Epidemic measures• Adopt emergency measures to ensure a safe water

supply. Chlorinate public water supplies, even if the source water appears to be uncontaminated.

• Initiate a thorough investigation designed to find the vehicle of infection and circumstances (time, place, person) of transmission, and plan control measures accordingly.

• Provide appropriate safe facilities for sewage disposal.