infectious diseases
Cholera
Introduction
Cholera is an acute infection of the small bowel by the gram-negative bacteriumVibrio cholerae, which secretes a toxin that causes copious watery diarrhea, leading to dehydration, oliguria, and circulatory collapse. Infection is typically through contaminated water or shellfish. Diagnosis is by culture or serology. Treatment is vigorous rehydration and electrolyte replacement plusdoxycycline. The causative organism,V. choleraeserogroups O1 and O139, is a short, curved, motile, aerobic, gram-negative bacillus that produces enterotoxin, a protein that induces hypersecretion of an isotonic electrolyte solution by the small-bowel mucosa. Humans are the only known natural host forV. cholerae. After penetrating the mucus layer, these organisms colonize the epithelial lining of the gut and secrete cholera toxin. These organisms do not invade the intestinal wall; thus, few or no white blood cells are found in stool. Both the El Tor and classic biotypes ofV. choleraeO1 can cause severe disease. However, mild or asymptomatic infection is much more common with the currently predominant El Tor biotype and with non-O1 and non-O139 serogroups ofV. cholerae. Cholera is spread by ingestion of water, shellfish, or other foods contaminated by the excrement of people with symptomatic or asymptomatic infection. Household contacts of patients with cholera are at high risk of infection, which probably occurs through shared sources of contaminated food and water. Person-to-person transmission is less likely to occur because a large inoculum of organism is needed to transmit the infection. Cholera is endemic in portions of Asia, the Middle East, Africa, South and Central America, and the Gulf Coast of the US. In 2010, an outbreak started in Haiti and lasted until 2017. It later spread to the Dominican Republic and Cuba. During this outbreak, over 820,000 people became ill, and nearly 10,000 died. Cases transported into Europe, Japan, and Australia have caused localized outbreaks. An outbreak in Yemen started in 2016 and has not yet ended. This outbreak has had even greater devastating effects. Over 2.5 million people in Yemen have become ill, and almost 4,000 have died. It is thought to be the largest, fastest-spreading cholera outbreak in modern history. In endemic areas, outbreaks usually occur during warm months. The incidence is highest in children. In newly affected areas, epidemics may occur during any season, and all ages are equally susceptible. A milder form of gastroenteritis is caused by Noncholera Vibrio Infections strains O1 and O139, which do not produce cholera toxin. Susceptibility to infection varies and is greater for people with blood type O. Because vibrios are sensitive to gastric acid, hypochlorhydria and achlorhydria are predisposing factors. People living in endemic areas gradually acquire a natural immunity. 