Foodborne Infection by Shigella- Shigellosis Food Poisoning
Shigella infection, also known as shigellosis, is a bacterial infection that affects the digestive system. It is caused by a group of bacteria called Shigella, which belong to the family of Enterobacteriaceae. Shigella bacteria can cause diarrhea, fever, abdominal pain, and sometimes bloody stools. Shigella infection is one of the most common causes of bacillary dysentery, which is a severe form of diarrhea that can damage the lining of the intestines.
Shigella infection is mainly reported in poor underdeveloped, and developing countries where there is a lack of hygiene, sanitation, and healthcare facilities. The mortality rate of shigellosis is high, especially in children under 5 years with malnutrition. The person suffering from Shigella infection undergoes impaired nutrition due to the heavy loss of electrolytes and blood during diarrhea which may lead to death of a person.
Shigella species are classified into four serogroups, namely S. dysenteriae (serogroup A), S. flexneri (serogroup B), S. boydii (serogroup C), and S. sonnei (serogroup D). Among these, S. dysenteriae Type 1 is responsible for causing deadly epidemic outbreaks, whereas other serotype causes minimum and rare disease.
Shigella infection is very contagious and can spread easily from one person to another through the fecal-oral route or through direct contact with contaminated feces. Ingestion of water and food contaminated with human feces are the primary sources of Shigella infection. Children and infants are more prone to shigellosis, mainly in poor and developing countries, due to a lack of sanitary facilities and good hygienic practices.
Shigella infection can be diagnosed by stool culture, immunological assays, or molecular techniques. The treatment of shigellosis depends on the severity of the infection and may include antibiotics, oral rehydration, and intravenous fluid therapy. The prevention and control of shigellosis require appropriate sanitation, good personal hygiene, proper disposal of feces, washing fruits and vegetables with chlorinated water before consuming, and proper refrigeration of food products.
In this article, we will discuss the biological characteristics, sources, and transmission, epidemiology, diseases and symptoms, mechanism of toxicity, laboratory diagnosis, treatment and prevention, and control of Shigella infection. We will also answer some frequently asked questions about shigellosis.
Shigella are bacteria that belong to the family Enterobacteriaceae, which includes many other pathogens such as Escherichia coli, Salmonella, and Yersinia. Shigella are classified into four species based on their antigenic and biochemical properties: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei. These species are further divided into 43 serotypes according to their O (somatic) and K (capsular) antigens.
Shigella are gram-negative, meaning that they do not retain the purple stain in the Gram staining method. They are also facultative anaerobes, meaning that they can grow with or without oxygen. They are non-sporulating, meaning that they do not form resistant spores that can survive harsh conditions. They are non-motile, meaning that they do not have flagella or other structures that enable them to move.
Shigella are prokaryotic rods, meaning that they have a simple cellular structure without a nucleus or membrane-bound organelles. They are about 0.4 to 0.6 micrometers in diameter and 1 to 3 micrometers in length. They have an optimum temperature range of 7 to 46°C and can resist 5% NaCl and pH extremes. They can survive the harsh physical and chemical conditions of the stomach and the small intestine, but they are sensitive to pasteurization temperature.
Shigella have several virulence factors that enable them to cause infection and disease in humans. These include:
- The ability to invade and multiply within the epithelial cells of the colon, causing tissue damage and inflammation.
- The production of Shiga toxin by S. dysenteriae and some strains of S. flexneri, which inhibits protein synthesis and induces cell death in the host cells.
- The presence of a lipopolysaccharide (LPS) layer on the outer membrane, which acts as an endotoxin and triggers an immune response in the host.
- The possession of a large plasmid that encodes genes for invasion, cell-to-cell spread, and antibiotic resistance.
Shigella are closely related to E. coli genetically, but they differ in some phenotypic characteristics, such as lactose fermentation, indole production, and gas formation. Shigella can be distinguished from other enteric bacteria by using selective and differential media such as MacConkey agar, Salmonella-Shigella agar, and Xylose-Lysine Deoxycholate agar. Shigella can also be identified by using biochemical tests, serological tests, immunological assays, and molecular techniques.
Shigella infection is mainly transmitted through the fecal-oral route, which means that the bacteria can spread from the stool of an infected person to the mouth of another person. This can happen in various ways, such as:
- Eating food or drinking water that is contaminated with Shigella bacteria. This can occur when food handlers or preparers do not wash their hands properly after using the toilet or changing diapers or when food is washed or irrigated with contaminated water. Foods that are consumed raw, such as salads, fruits, and vegetables, are more likely to be contaminated with Shigella bacteria than cooked foods.
- Having direct contact with an infected person or their feces. This can include oral-anal sex, diaper changing, caring for a sick person, or touching surfaces that are contaminated with feces, such as toys, bathroom fixtures, changing tables, or diaper pails.
- Swallowing recreational water, such as lake or river water, that is contaminated with Shigella bacteria. This can happen when people swim or play in water that has been polluted by sewage or animal waste or when they accidentally ingest water while swimming.
The main reservoir of Shigella bacteria is the human intestinal tract. Shigella infection is rarely found in animals, although some cases have been reported in monkeys and guinea pigs.
Shigella bacteria are very infectious, and it only takes a small amount (10 to 100 cells) to make someone sick with shigellosis. People who are infected with Shigella bacteria can shed (get rid of) the bacteria in their stool for up to two weeks after their symptoms have gone away, even if they do not feel sick anymore. This means that they can still infect others during this period.
Some groups of people are more likely to get Shigella infection than others. These include:
- Young children, especially those under 5 years of age, are more exposed to fecal contamination and have less developed immune systems. Children can also spread the infection easily among themselves and to their family members and caregivers in settings such as childcare and school.
- Travelers to countries that do not have adequate sanitation, hygiene, and health care facilities. Travelers may get infected by eating or drinking contaminated food or water or by having contact with infected people or animals. They may also encounter strains of Shigella bacteria that are resistant to common antibiotics, making the infection harder to treat.
- Men who have sex with men (MSM), especially gay or bisexual men, are more likely to have oral-anal contact with an infected partner. Many outbreaks of shigellosis among MSM have been reported worldwide, and some strains of Shigella bacteria have been found to be resistant to antibiotics commonly used for treating sexually transmitted infections (STIs).
- People who have weakened immune systems due to illness (such as HIV) or medical treatment (such as chemotherapy for cancer) are more susceptible to severe complications from shigellosis, such as bloodstream infections or hemolytic uremic syndrome (HUS).
- Shigella infection is a major cause of morbidity and mortality worldwide, especially in resource-limited countries where there is a lack of hygiene, sanitation, and healthcare facilities.
- Shigella infection is mainly transmitted through the fecal-oral route, either by direct contact with an infected person or by ingestion of contaminated food or water.
- Shigella can survive to transit through the stomach since they are less susceptible to acid than other bacteria; for this reason, as few as 10 to 100 organisms can cause disease.
- Humans are the only natural reservoir for Shigella infection. Animals are rarely infected by Shigella.
- Shigella infection can occur in any age group, but children under 5 years of age are more susceptible and account for most of the cases and deaths.
- Shigella infection is more common in crowded settings, such as daycare centers, nursing homes, refugee camps, and prisons.
- Men who have sex with men (MSM) are also at increased risk of acquiring Shigella infection through oral-anal contact.
- Shigella species are classified into four serogroups: S. dysenteriae (serogroup A), S. flexneri (serogroup B), S. boydii (serogroup C), and S. sonnei (serogroup D).
- S. dysenteriae type 1 is the most virulent and causes severe epidemics of dysentery, especially in Africa and Asia. It produces a potent toxin called Shiga toxin that can damage the kidneys and the nervous system.
- S. sonnet is the most common cause of Shigella infection in high-income countries, such as the United States and Europe. It causes mild to moderate disease and rarely produces Shiga toxin.
- S. flexneri is the predominant cause of Shigella infection in low- and middle-income countries, where it causes moderate to severe disease. It can also produce Shiga toxin in some strains.
- S. boydii is the least common cause of Shigella infection globally and causes mild to moderate disease. It does not produce Shiga toxin.
- According to the World Health Organization (WHO), it is estimated that 165 million cases of shigellosis occur annually worldwide, with 55,000 associated deaths, mostly in children under 5 years of age.
- In the United States, about 500,000 cases of shigellosis are reported each year, with an estimated 70 deaths.
Shigella infection, or shigellosis, is a type of food poisoning that affects the digestive system. It causes inflammation and damage to the lining of the intestines, especially the colon. Shigellosis can range from mild to severe, depending on the type and amount of bacteria ingested.
The most common symptom of shigellosis is diarrhea, which can be watery, bloody, or contain mucus or pus. Diarrhea can lead to dehydration and electrolyte imbalance if not treated promptly. Other symptoms may include:
- Stomach pain or cramps
- Nausea or vomiting
- Loss of appetite
- Fatigue or malaise
- Tenesmus (feeling the need to pass stool even when the bowels are empty)
Symptoms usually begin within one to two days after contact with Shigella, but they can appear as early as 12 hours or as late as seven days after exposure. The duration of symptoms varies from person to person, but they typically last for five to seven days. However, some people may have no symptoms at all, while others may have chronic or recurrent diarrhea.
Shigellosis can also cause complications in some cases, such as:
- Post-infectious arthritis: a condition that causes joint pain and swelling after an infection
- Bloodstream infections: a serious complication that occurs when bacteria enter the blood and cause sepsis (a life-threatening response to infection)
- Hemolytic-uremic syndrome: a rare but potentially fatal condition that causes kidney failure and low red blood cell count due to damage to the blood vessels
- Seizures: abnormal electrical activity in the brain that can cause convulsions or loss of consciousness
- Toxic megacolon: a rare but life-threatening condition that causes the colon to become enlarged and paralyzed due to severe inflammation
Shigellosis is diagnosed by testing a stool sample for the presence of Shigella bacteria or their toxins. Treatment depends on the severity of the infection and may include antibiotics, oral rehydration therapy, intravenous fluids, and supportive care.
The best way to prevent shigellosis is by practicing good hygiene, such as washing hands frequently with soap and water, especially before eating or preparing food, after using the toilet or changing diapers, and after contact with animals or contaminated surfaces. Other preventive measures include avoiding drinking or swimming in unsafe water, cooking food thoroughly, refrigerating leftovers promptly, and avoiding sexual contact with infected persons.
Shigellosis is a common and contagious disease that can cause significant morbidity and mortality, especially in children under five years of age and in developing countries. It is important to seek medical attention if you have symptoms of shigellosis or suspect you have been exposed to Shigella bacteria.
Shigella infection causes damage to the intestinal epithelium and triggers inflammation and diarrhea by several mechanisms :
- Invasion and spread: Shigella bacteria invade the colonic mucosa through specialized cells called M cells, which are located in the Peyer`s patches. The bacteria escape from the vacuoles and multiply in the cytoplasm of the M cells. They then use actin-based motility to spread to adjacent epithelial cells, forming membrane protrusions that are engulfed by the neighboring cells. This process allows Shigella to avoid the extracellular environment and the host immune system.
- Inflammation: Shigella bacteria induce a strong inflammatory response in the colon by several mechanisms, such as activating the inflammasome, releasing lipopolysaccharide (LPS), stimulating cytokine production, and inducing apoptosis and necrosis of infected cells. The inflammation causes tissue damage, ulceration, and bleeding, as well as increased fluid secretion and motility, leading to watery and bloody diarrhea.
- Toxin production: Some strains of Shigella produce toxins that contribute to the pathogenesis of infection. S. flexneri strains produce two enterotoxins, ShET1 and ShET2, which may increase chloride secretion and inhibit sodium absorption in the colon, resulting in osmotic diarrhea. S. dysenteriae strains produce a potent cytotoxin called Shiga toxin, which inhibits protein synthesis in host cells by cleaving a specific ribosomal RNA subunit. Shiga toxin can also enter the bloodstream and cause hemolytic uremic syndrome (HUS), a life-threatening complication characterized by hemolytic anemia, thrombocytopenia, and renal failure.
Shigella infection can be confirmed by testing a stool sample of the patient with clinical signs of dysentery. The sample should be collected and tested as soon as possible, as the bacteria may not survive long outside the host body. There are different methods to diagnose shigella infection, such as:
- Bacterial culture methods: The stool sample is inoculated on selective media, such as MacConkey agar, Salmonella-Shigella agar, or Xylose-Lysine Deoxycholate agar, to isolate and identify the bacteria. Sometimes, a rectal swab can also be used for culture. The culture results can take 24 to 48 hours.
- Bioassays: Some animals, such as guinea pigs, rodents, rabbits, and monkeys, can be infected orally with Shigella to observe the effects of the bacteria. Some animals may show inflammatory reactions in the eye or tissue damage in the large intestine. However, this method is not widely used due to ethical issues.
- Immunological assays: These are rapid tests that detect the antigens or antibodies of Shigella in the stool sample or serum. They include enzyme immunoassay (EIA), latex agglutination test, dipstick immunoassay, and Wellcolex Color Shigella test (WCT-Shigella). These tests are easy to use, cheap, and have high sensitivity and specificity.
- Molecular techniques: These are tests that detect the genetic material of Shigella in the stool sample using polymerase chain reaction (PCR) or other methods. They can target specific genes, such as ipaH, virA, viral, LPS, and plasmid DNA, to identify the species and serotype of Shigella. They can also detect antibiotic resistance genes and toxin genes. These tests are fast, accurate, and reliable.
The choice of diagnostic method depends on the availability of resources, the severity of the infection, and the epidemiological situation. The diagnosis of shigella infection can help guide the appropriate treatment and prevention measures.
Shigellosis is a bacterial infection that causes diarrhea, fever, and abdominal pain. It usually gets better on its own within a week, but some cases may require medical treatment. Here are some of the treatment options for shigellosis:
- Fluid replacement: The most important treatment for shigellosis is to drink plenty of fluids to prevent dehydration. Oral rehydration solutions (ORS) or intravenous fluids may be given to replace the lost water and electrolytes.
- Antibiotics: Antibiotics can shorten the duration and severity of symptoms and reduce the risk of spreading the infection to others. However, some strains of Shigella are resistant to certain antibiotics, so your doctor may test your stool sample to identify the best antibiotic for you. Some of the commonly used antibiotics for shigellosis are ciprofloxacin, azithromycin, and third-generation cephalosporins.
- Self-care: You should avoid anti-diarrheal drugs, such as loperamide or diphenoxylate, with atropine, as they may make your condition worse. You should also rest well and eat bland foods that are easy to digest, such as rice, bananas, toast, and applesauce. You should avoid foods that may irritate your digestive system, such as dairy products, spicy foods, raw fruits and vegetables, and fatty foods.
- Specialist care: If you have a weakened immune system, such as due to HIV infection or chemotherapy, you may need to see an infectious disease specialist who can monitor your condition and prescribe appropriate treatment. You may also need to see a specialist if you develop complications of shigellosis, such as post-infectious arthritis, bloodstream infections, hemolytic-uremic syndrome, seizures, or toxic megacolon.
Shigellosis can be a serious illness that requires prompt treatment. If you have symptoms of shigellosis, you should contact your healthcare provider as soon as possible and follow their advice. You should also take steps to prevent spreading the infection to others by washing your hands frequently, avoiding contact with sick people, and disposing of your feces properly.
Shigellosis is a highly contagious disease that can spread easily from one person to another through the fecal-oral route or through direct contact with an infected person. Therefore, the most effective way of preventing shigellosis is to practice good sanitation, personal hygiene, and proper disposal of feces. Some of the specific steps that can help prevent and control shigellosis are:
- Wash hands frequently with soap and water, especially before and after any sexual activity, before preparing food or eating, after using the bathroom or changing a diaper, and after cleaning up after someone who went to the bathroom.
- Avoid preparing food or sharing food with anyone if you are sick or have symptoms of shigellosis.
- Do not swim or have sex for at least two weeks after you no longer have diarrhea.
- Stay home from school or work if you are sick or until your health department says it is safe to return.
- Avoid swallowing water from ponds, lakes, or swimming pools that may be contaminated with feces.
- When traveling internationally, follow safe food and water habits and wash hands often with soap and water. Avoid salads, unwashed fruits and vegetables, milk, luncheon meat, and other foods that may be contaminated.
- Clean and disinfect surfaces and objects that may be contaminated with feces, such as toilets, sinks, countertops, toys, and diaper-changing areas. Use a bleach-based solution (1/4 cup of bleach per gallon of water) or a commercial disinfectant.
- If you work in a healthcare, food service, or childcare setting, follow the infection control guidelines of your facility and report any cases of shigellosis to your supervisor and health department.
By following these prevention and control measures, you can help protect yourself and your loved ones from getting sick with shigellosis and reduce the risk of outbreaks in your community.
In this section, we will answer some of the common questions that people may have about shigellosis, such as:
- What is shigellosis?
- How does shigellosis spread?
- What are the symptoms of shigellosis?
- Who is at risk of getting shigellosis?
- How is shigellosis diagnosed and treated?
- How can shigellosis be prevented and controlled?
What is shigellosis?
Shigellosis is a disease caused by a group of bacteria called Shigella. These bacteria infect the intestinal tract and cause inflammation and damage to the lining of the colon. Shigellosis can cause fever, abdominal pain, and bloody or watery diarrhea. Shigellosis can be mild or severe, and sometimes it can lead to serious complications such as dehydration, arthritis, seizures, or kidney failure.
How does shigellosis spread?
Shigellosis spreads easily from one person to another through the fecal-oral route. This means that you can get infected by swallowing Shigella bacteria that are present in the feces (poop) of an infected person or animal. Some of the ways that Shigella bacteria can get into your mouth are :
- Getting Shigella on your hands and touching your mouth. This can happen by touching contaminated surfaces, changing diapers, or caring for someone with shigellosis.
- Eating food or drinking water that is contaminated with Shigella. This can happen by eating raw or undercooked food, drinking untreated water, or consuming food or water that has been handled by someone with shigellosis.
- Swallowing water that contains Shigella. This can happen by swimming or playing in lakes, ponds, pools, or fountains that are contaminated with sewage or fecal matter.
- Having oral or anal sex with someone who has shigellosis or who has recently recovered from shigellosis.
What are the symptoms of shigellosis?
The symptoms of shigellosis usually start 1 to 3 days after exposure to Shigella bacteria, but they can range from 12 hours to 7 days. The most common symptoms are :
- Diarrhea that can be bloody or watery
- Stomach pain
- Feeling the need to pass stool even when the bowels are empty
Some people may also experience nausea, vomiting, fatigue, malaise, or headache. The symptoms usually last for 5 to 7 days, but they can be longer or shorter depending on the severity of the infection and the type of Shigella bacteria involved. Some people may have no symptoms at all, but they can still spread the infection to others.
Who is at risk of getting shigellosis?
Anyone can get shigellosis, but some people are more likely to get infected or have severe illness than others. These include :
- Children younger than 5 years old
- Travelers to developing countries where sanitation and hygiene are poor
- People who live in crowded or unsanitary conditions
- People who have weakened immune systems due to HIV/AIDS, cancer, diabetes, or other conditions
- Men who have sex with men
How is shigellosis diagnosed and treated?
Shigellosis is diagnosed by testing a stool sample for the presence of Shigella bacteria. Sometimes, a rectal swab may also be used. The test results can help identify the type and strain of Shigella bacteria involved and determine the best treatment options.
Shigellosis usually gets better on its own within a week without any specific treatment. However, some cases may require antibiotic treatment to reduce the duration and severity of symptoms and prevent complications. Antibiotics may also be recommended for people who are at high risk of severe illness or who have close contact with others who are vulnerable to infection. However, some strains of Shigella bacteria have become resistant to certain antibiotics, making them harder to treat.
In addition to antibiotics, people with shigellosis should drink plenty of fluids or oral rehydration solutions to prevent dehydration caused by diarrhea. They should also avoid drugs that stop diarrhea or slow down gut movement, such as loperamide or atropine, as they can make shigellosis worse. They should also get adequate rest and eat bland foods that are easy to digest.
How can shigellosis be prevented and controlled?
The most effective way of preventing and controlling shigellosis is to practice good sanitation and personal hygiene and avoid exposure to contaminated food, water, or people. Some of the steps that you can take are :
- Wash your hands frequently with soap and water, especially before eating or preparing food, after using the toilet or changing diapers, after caring for someone with shigellosis, and after touching animals or their feces.
- Cook food thoroughly and avoid raw or undercooked food that may be contaminated with Shigella.
- Wash fruits and vegetables with clean water before eating them.
- Refrigerate food promptly and avoid leaving it at room temperature for too long.
- Drink only treated water or bottled water and avoid ice made from untreated water.
- Avoid swimming or playing in water that may be contaminated with sewage or fecal matter.
- Use condoms during oral or anal sex with someone who has shigellosis or who has recently recovered from shigellosis.
If you have shigellosis, you should also take steps to prevent spreading the infection to others. These include :
- Stay home from work, school, childcare, or other activities until you have been free of diarrhea for at least 24 hours.
- Do not prepare food for others until you have been free of diarrhea for at least 48 hours.
- Dispose of your feces safely, and do not share toilets with others.
- Clean and disinfect surfaces and objects that may be contaminated with Shigella bacteria.
There is currently no vaccine available for shigellosis. However, research is ongoing to develop new vaccines that can protect against different types of Shigella bacteria.
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