Tiny germs can make us sick. They live in people and gorillas. These germs can hurt your tummy. They make you go to the bathroom a lot. It is good to stay clean. Can you wash your hands?
Small germs can make people sick. These germs live in humans and gorillas. They can hurt your tummy. They make you go to the bathroom a lot. Sometimes your tummy will feel very sore. You might also feel hot or sick to your stomach. These germs can spread through food or water. It is important to stay healthy. Can you help keep the germs away?
Shigella is a type of germ called bacteria. It is shaped like a rod. A doctor named Kiyoshi Shiga found it in 1897. This germ lives in humans and gorillas. It can make people very sick.
People get sick by eating or drinking things with the germ. Once inside, the bacteria move into the colon. The colon is a part of your gut. The bacteria use a special tool to work. It is called a type-III secretion system. This tool acts like a tiny syringe. It lets out proteins into human cells. These proteins help the bacteria spread.
Shigella causes a sickness called shigellosis. It causes bad diarrhea. Sometimes the stool has blood or mucus in it. This is called dysentery. People may also have a fever or a stomach ache. Symptoms can start in two to four days. They can last for many weeks. Shigella is a big cause of sickness in children. It causes millions of cases every year. Some people may even die from it.
Shigella is a group of tiny living things called bacteria. These bacteria are shaped like small rods. They are part of a larger family of germs. Scientists say they are closely related to E. coli. This group of bacteria can cause a sickness called shigellosis. It is a leading cause of bad diarrhea around the world. It is especially hard on children in South Asia and Africa.
Getting sick usually happens by eating or drinking something with the bacteria. Once inside, the bacteria find their way to the colon. The colon is a part of your gut. The bacteria use a special tool called a type-III secretion system. You can think of this tool like a tiny biological syringe. It shoots proteins into the cells of your body. These proteins help the bacteria move and spread to other cells. This process causes inflammation, which is when the area gets red and swollen.
A doctor named Kiyoshi Shiga discovered these bacteria. He was a physician from Japan. He studied at the Tokyo Imperial University School of Medicine. He started working as a research assistant in 1892. In 1897, he studied a large outbreak of dysentery. He looked at 32 sick patients to find the cause. He successfully isolated the bacteria and even worked on a vaccine.
There are different groups of Shigella. These are called serogroups. Group A is S. dysenteriae. Group B is S. flexneri. Group C is S. boydii. Group D is S. sonnei. S. flexneri is the most common type in the developing world. It causes 60% of cases there. In developed countries, S. sonnei is more common. It causes 77% of cases in those areas. Every year, there are an estimated 80 to 165 million cases of this sickness.
When you are sick, you might feel very unwell. You may have a fever, nausea, or stomach cramps. Some people also get vomiting or gas. The diarrhea can be very painful. Sometimes, the stool contains blood or mucus. This specific type of sickness is called dysentery. Symptoms usually start two to four days after you swallow the bacteria. They can last for a few days or even many weeks.
Shigella is a genus of rod-shaped bacteria that causes a disease called shigellosis. These bacteria are Gram-negative and facultatively anaerobic, meaning they can live with or without oxygen. They are non-spore-forming and nonmotile, so they do not move on their own. Scientists have found that Shigella is genetically nested within the Escherichia coli family. Because of this close relationship, many phylogenetic studies suggest it is actually a subgroup of E. coli. Shigella is a major global health concern because it is a leading cause of bacterial diarrhea. It is specifically one of the top four pathogens causing moderate-to-severe diarrhea in children across Africa and South Asia.
The infection process usually begins when a person ingests the bacteria. It does not take many bacteria to make someone sick. Depending on the host's health, fewer than 100 bacterial cells may cause an infection. Once inside the body, Shigella targets the epithelial lining of the colon. It enters the host by invading M-cells, which are cells interspersed within the epithelia of the small intestine. The bacteria prefer the basolateral side of these cells rather than the apical surface. Once they have invaded, the bacteria multiply inside the cells and spread to neighboring cells. This process causes severe inflammation and the death of the cells lining the colon.
To survive and spread, Shigella uses a sophisticated mechanism called a type-III secretion system. You can think of this system as a biological syringe. It allows the bacteria to translocate toxic effector proteins directly into the host cell. These proteins can change how the target cell works. For example, they can cause the lysis of vacuolar membranes. They can also reorganize actin polymerization, which helps the bacteria move inside the host cell. One specific protein, called IcsA, triggers actin reorganization by recruiting N-WASP and Arp2/3 complexes. This helps the bacteria spread from one cell to another.
Shigella also has ways to trick the body's immune system. The bacteria use their secretion system to release OspC1 and OspC3 proteins. These proteins work to suppress the interferon signaling pathway. This pathway is a key part of the host's defense against infection. Specifically, these proteins target the JAK/STAT signaling pathway to prevent the expression of interferon-stimulated genes. They do this by binding to calmodulin, a protein required for the phosphorylation of STAT. The bacterial proteins mimic a protein called CaMKII, which causes calmodulin to make a mistake. This prevents the normal immune response from working correctly.
Scientists classify Shigella into different groups based on their characteristics. There are three main serogroups: Serogroup A, B, and C, plus Serogroup D. Serogroup A is S. dysenteriae, which contains 15 serotypes. Serogroup B is S. flexneri, which has 9 serotypes. Serogroup C is S. boydii, which includes 19 serotypes. Serogroup D is S. sonnei, which has only one serotype. While groups A through C are physiologically similar, S. sonnei can be told apart using biochemical metabolism assays. Different species cause different patterns of disease depending on where you live.
These different species have very different impacts on the world. S. flexneri is the most common species found worldwide. It accounts for 60% of Shigella cases in the developing world. In contrast, S. sonnei is the most common in the developed world, causing 77% of cases there. However, S. sonnei only accounts for 15% of cases in the developing world. S. dysenteriae is often responsible for large epidemics of dysentery. These outbreaks frequently happen in confined populations, such as those in refugee camps. Some strains also produce dangerous toxins. S. flexneri produces ShET1 and ShET2, while S. dysenteriae produces the hemolytic Shiga toxin.
The history of this discovery is tied to the work of Kiyoshi Shiga. He was a Japanese physician who studied at the Tokyo Imperial University School of Medicine. After graduating, he worked as a research assistant for Shibasaburo Kitasato. In 1897, Shiga studied a massive outbreak of a disease known in Japan as sekiri. This epidemic affected more than 91,000 people, and the mortality rate was over 20%. By studying 32 patients and using Koch's postulates, Shiga successfully isolated the bacterium. He also identified how the Shiga toxin is produced and worked to create a vaccine.
The impact of Shigella on human health is massive. Every year, there are an estimated 80 to 165 million cases of shigellosis. These infections lead to between 74,000 and 600,000 deaths annually. Symptoms can appear two to four days after ingestion, though they can sometimes take a week. Common symptoms include fever, nausea, vomiting, stomach cramps, and flatulence. The infection often causes large, painful bowel movements. Because the stool may contain blood, mucus, or pus, the condition is often called dysentery. In rare instances, young children may even experience seizures.
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