Cholera (vibrio cholerae)

2021-08-19 06:15 PM

Cholera bacteria have oxidase, ferment without producing glucose, sucrose, D-mannitol, maltose, do not ferment arabinose. Positive indole reaction

The genus Vibrio belongs to the family Vibrionaceae. They are comma-shaped, slightly curved rods, Gram-negative, non-spore-forming, motile by cilia on one end, oxidase-positive... The genus Vibrio is divided into:

Vibrio cholerae O1: belongs to serogroup O1 capable of producing enterotoxins and causing cholera. Vibrio cholerae O1 includes the classical biotype and the El Tor biotype. These biotypes agglutinate with group 01 antisera. In this group, there are 3 serotypes, Ogawa, Inaba, and Hikojima.

Vibrio cholerae non-O1/non-O139: includes serogroups from O2 - O138 that are not capable of causing cholera. Has biochemical properties similar to V.cholerae O1 but does not agglutinate with antisera O1. The infections caused by this group are often related to the environment, they cause acute enteritis, but the mechanism of the disease is still unknown.

Vibrio cholerae O139: the causative agent of cholera was first discovered in 1992 in India and Bangladesh. Its virulence is enterotoxin and toxin co-regulated pili antigen (Toxin coregulated pili - TCP).

Others Vibrio: V. mimicus; V. parahaemolyticus; V.hollisae. V. fluvialis; V.furnissii; V.vulnificus; V.alginolyticus; V.damsela; V.cincinnatiensis; V.metschnikovii.

Biological characteristics

Shape

Cholera short rod, slightly curved arc or comma, Gram-negative, very motile by a hair on the tip, no shell, no sporophyte.

Culture properties

Cholera bacteria are very aerobic, growing on normal nutrient media, alkaline pH. Usually use peptone water pH 8.5, TCBS agar (thiosulfate - Citrate - Bile salt) pH 8.6, TTGA (Taurocholate - Tellurite - Gelatin Agar) pH 8.5 to culture isolates cholera bacteria.

Biochemical properties

Cholera bacteria have oxidase, ferment without producing glucose, sucrose, D-mannitol, maltose, do not ferment arabinose. The indole test is positive, the Voges-Proskauer reaction is negative for the classical type and positive for the El Tor type.

Antigen structure

Stem antigens are lipopolysaccharide in nature. It determines the immunogenicity of the classical cholera vaccine (dead cholera vaccine). It is distinguished into several “O” serogroups. V. cholerae gave birth to the classical type and to the El Tor type of serogroup O1. In group O1 there are 3 serotypes: Ogawa, Inaba, and Hikojima.

Hair antigen H: No practical value.

The enterotoxin antigen is essentially a protein, and the enterotoxin of V.cholerae 01 stimulates the body to produce antitoxin.

Resistance abilities

Cholera bacteria die at a temperature of 100oC or 80oC / 5 minutes and are destroyed by chemicals such as chloramine, cresyl, lime... Dryness and sunlight also make bacteria easy to die. In ice water, seawater, pond water, bacteria live for several days.

Possibility to cause disease

Pathophysiology

Cholera bacteria enter the body through the digestive tract, they have to cross the gastric acid barrier of the stomach with an acidic pH to enter the small intestine, where the pH is suitable for the growth of bacteria. The normal acidity of gastric juice is a great obstacle to the pathogenesis of cholera. Entering the small intestine, V. cholerae adheres to intestinal mucosal cells thanks to adhesion factors such as TCP antigen, mannose-sensitive red blood cell agglutination antigen..., bacteria multiply and secrete toxins gut factor. The bacteria did not penetrate the intestinal mucosal cells.

The enterotoxin of cholera bacteria is a protein consisting of 2 subunits A (Active) and B (Binding) with separate functions. Subunit A has two subunits A1 and A2, subunit B has 5 subunits B1, B2, B3, B4, and B5. The B subunit has the function of binding the enterotoxin to the ganglioside GM1 receptor on the membrane of intestinal mucosal cells, while the A subunit, mainly A1 penetrates the inside of the cell, activates the enzyme adenylate cyclase, increasing the concentration of the enzyme adenylate cyclase. The level of intracellular cyclic AMP causes intestinal mucosal cells to reduce Na + absorption, increase water and Cl- secretion, causing acute diarrhea. If left untreated, the patient will die from dehydration and loss of electrolytes.

Cholera toxin also induces cellular immunosuppression by acting directly on macrophages and T lymphocytes.

During the pathogenesis of cholera, cholera toxins and bacteria do not cause damage to the intestinal mucosa. Therefore, the mechanism of reabsorption of salt, water, and glucose remains intact. This is the physiological basis for rehydration oral solution containing electrolytes and glucose (oresol) works well (glucose here to facilitate reabsorbed Na higher, rather than to provide energy quantity).

Possibility to cause disease

Under normal natural conditions, V. cholerae only causes cholera in humans. Cholera is an acute infectious disease, very contagious, causing large epidemics. The incubation period is 2 to 5 days. Characteristic signs of the full-blown period of the disease are diarrhea and vomiting, loose and white stools like rice water. Patients lose water, lose salt very quickly, can lose 1 liter of water in 1 hour, so it only takes a few hours to appear acute dehydration syndrome, making the whole body lose very quickly and very badly. If left untreated, mortality is very high (50 to 60%).

Clinically, cholera has a wide variety of manifestations ranging from a mild, easily overlooked form to a severe form with typical cholera syndrome.

Immune

The humoral immune response in cholera results in the appearance of IgG in the blood and IgA secreted in the intestinal mucosa. These antibodies work against the bacterial cell wall, prevent bacteria from adhering to the mucosa, and against cholera toxin, prevent cholera toxin (subunit B) from attaching to the intestinal mucosal cell membrane.

Epidemiology

Cholera is transmitted by the gastrointestinal tract through contaminated food and water. The source of infection is sick and healthy people carrying cholera bacteria.

Since 1817, there have been 7 cholera epidemics in the world. The six cholera pandemics were all caused by the classical V. cholerae. The 7th cholera epidemic caused by V.cholerae born type El Tor, started in 1961 and continues to this day. V.cholerae El Tor is resistant to chemical agents, persists longer in humans, and lives longer in nature than classically subtyped V.cholerae. In addition, in El Tor cholera endemic areas, severe cases are often less and mild cases without symptoms are more.

Beginning in 1992, cholera epidemic occurred in Madras and many other parts of India and Bangladesh caused by Vibrio cholerae O139 with the same pathogenesis as Vibrio cholerae O1. Then cholera caused by strain O139 spread to other countries.

Microbiological diagnosis

Direct diagnosis

Cholera is an acute disease, so stool culture to isolate cholera is the best diagnostic method.

Specimens

Fecal collection early in the early stages of the disease before antibiotic treatment. Stool specimens should be brought to the laboratory within 2 hours. If sending samples away, they must be placed in Cary Blair's storage and transport environment and brought to the laboratory as soon as possible.

Microscopic examination

A fresh examination can show that cholera bacteria move very quickly. Gram stain showed many Gram-negative bacteria. Microscopic examination of the specimen has a preliminary diagnostic effect.

Viral Culture

Specimens are inoculated into selective and enriched media for bacterial isolation. Determination of biological and chemical properties. Do a slide agglutination reaction with polyvalent antisera O1 and with monovalent antisera specific to the type Inaba or Ogawa to confirm the diagnosis.

Quick diagnostic method

To quickly identify cholera bacteria can use techniques such as bacteria immobilization, direct fluorescent antibodies.

Indirect diagnosis

Serological methods are not helpful in diagnosing the disease. It can be used in epidemiological investigations.

Prevention and cure

Prevention

General room

Epidemiological surveillance proactively detects disease sources early, promptly isolates, surrounds and handles.

Clean up the living environment by measures such as treating garbage and wastewater in accordance with sanitary requirements; food hygiene inspection; eat cooked, drink hot and stay clean...

Specific disease prevention

Dead vaccines, administered intradermally, have low potency and a short duration of protection. Currently, many countries do not use this classic vaccine.

Live attenuated vaccines: create non-toxic mutant strains to make oral vaccines. Currently testing.

Dead or oral vaccine: This vaccine can be inactivated whole-cell alone or in combination with the B subunit of purified cholera toxin.

In Vietnam, a single oral cholera vaccine containing classical Vibrio cholerae O1 and El Tor cells is inactivated by heat and formalin. Currently testing inactivated cholera vaccines (Vaccine biv-WC) including Vibrio cholerae O1 and Vibrio cholerae O139.

Curing

Rehydration and electrolytes must be given early, quickly, and sufficiently for the patient. Use antibiotics Tetracycline, Doxycycline ...