Viruses, The Pancreas and Type 1 Diabetes - Exploring the Links
Type 1 diabetes is a condition in which the pancreas no longer makes insulin, a hormone that enables glucose molecules to leave the blood and enter the body's cells. As a result, glucose collects in the blood and may reach a dangerous level. Glucose is also known as blood sugar. It's obtained from food and used by cells as an energy source. High blood sugar can damage blood vessels and cause organ and nerve damage. One of the factors that may cause at least some cases of type 1 diabetes is an infection by certain viruses.
People with type 1 diabetes can manage their condition with the aid of insulin injections or an insulin pump, although they always have to be careful with their diet, exercise and the amount of insulin that they receive. High blood sugar is dangerous, but so is low blood sugar. Patients have to measure their blood sugar level and make adjustments to their insulin dose multiple times during the day.
Type 1 diabetes may eventually cause eye, kidney or nerve problems, even when it's treated. It would be wonderful to prevent or cure the disease. In order to do this, researchers have to know its cause (or causes).
Type 1 Diabetes - An Autoimmune Disease
Type 1 diabetes is generally considered to be an autoimmune disease. Our immune systems protect us from disease by attacking - or attempting to attack - invaders such as viruses and bacteria. In people with an autoimmune condition, the immune system mistakenly attacks the person's own cells. It's thought that people with type 1 diabetes have a genetic predisposition to develop the disease. However, even with this predisposition, diabetes won't develop unless an environmental trigger stimulates the immune system to destroy the beta cells in the pancreas. These cells make the insulin.
There is a growing body of evidence suggesting that one of the environmental triggers for type 1 diabetes could be an infection by a virus. Several types of virus have been implicated in the disease process. Although viruses aren't thought to cause all cases of the disease, they may well be responsible for some cases.
What is Type 1 Diabetes?
What is the Difference Between Type 1 and Type 2 Diabetes?
In people with type 1 diabetes, also known as type 1 diabetes mellitus, the pancreas produces no or very little insulin. Glucose is unable to enter cells and collects in the blood. Most people with type 1 diabetes are diagnosed as children or as teenagers. In fact, the disorder used to be called juvenile diabetes. Adults may also develop type 1 diabetes, however.
In people with type 2 diabetes, the pancreas is still producing insulin. However, the body's cells aren't responding to this insulin, a condition known as insulin resistance. Once again, glucose collects in the blood. Most people with type 2 diabetes are diagnosed as adults. However, as the number of obese children increases, more cases of type 2 diabetes in children are being reported. Obesity is a risk factor for type 2 diabetes.
Type 2 Diabetes and Insulin Resistance
Symptoms of Diabetes
The increase in blood sugar level causes excessive thirst and urination in untreated diabetics. Other symptoms may include extreme tiredness, extreme hunger and unexplained weight loss. These symptoms may be present in both types of diabetes. There may be additional symptoms in type 2 diabetes, such as slow healing of wounds, tingling or numbness in the hands or feet, blurred vision and frequent infections.
Type 1 Diabetes Symptoms
What are Enteroviruses?
A virus consists of a coat of protein surrounding genetic material. This material is usually DNA (the same chemical which contains our genetic code) but is sometimes a related chemical known as RNA. The enteroviruses are small RNA viruses that multiply in the gut.
Enteroviruses are primarily transmitted from person to person by the transfer of respiratory secretions or by the contamination of objects by feces. If a contaminated hand or other item contacts the mouth or nose, a person may become infected by the virus. This is one reason why washroom hygiene is very important when using a restroom. Even a tiny sample of feces can contain many bacteria and viruses.
There are many types of enteroviruses and they can cause many diseases. One type that has been linked to type 1 diabetes is the group known as coxsackieviruses.
DNA stands for deoxyribonucleic acid. It's an amazing substance that controls many of the characteristics of living things and viruses. In humans, RNA, or ribonucleic acid, helps DNA to do its job. In enteroviruses, however, RNA replaces DNA.
Enteroviruses and Type 1 Diabetes
Medical researchers in Finland have found that people with type 1 diabetes are far more likely to have a persistent enterovirus infection in their intestinal mucosa than people without diabetes. The "mucosa" is the lining of the intestine. The researchers also found that the infection was associated with mucosal inflammation.
In addition, a survey by Australian researchers found that children with type 1 diabetes were nearly ten times as likely as other children to have an enterovirus infection. 4,448 children were involved in the study - some with type 1 diabetes and some who were healthy.
Some experiments - but not all - have found that people with type 1 diabetes have antibodies against enteroviruses in their bloodstream or bits of protein or RNA from the viruses in their blood.
The pancreas continues cells of different types. It produces digestive enzymes as well as the hormones insulin (made by beta cells) and glucagon (made by alpha cells). Glucagon has the opposite effect to insulin - it raises blood sugar level instead of lowering it. Researchers have found enteroviruses inside the pancreas in people with diabetes. The viruses are found in the Islets of Langerhans, the tissue that contains the beta cells, and only occasionally in other tissues in the pancreas.
Coxsackieviruses, Heart Disease and Diabetes
Do Enteroviruses Cause Diabetes?
The above observations strongly suggest that enteroviruses are linked to type 1 diabetes. However, they don't prove that the viruses actually cause the disease. The evidence could indicate that when a person becomes sick with diabetes they become more susceptible to an enterovirus infection. It could also indicate that the genetic susceptibility to type 1 diabetes is accompanied by a genetic susceptibility to an enterovirus infection.
In lab mice, a direct connection between enteroviruses and the development of diabetes has been demonstrated. Enteroviruses have been administered to healthy animals and have caused prolonged infections of the pancreas and intestine. Specific enteroviruses have caused beta cell damage in the pancreas and the development of type 1 diabetes. This type of direct evidence isn't available for humans.
A Flu Virus Infecting the Body
Flu Viruses and Type 1 Diabetes
In a recent experiment, researchers added two types of flu viruses to human pancreatic tissue. They found that the viruses multiplied very well inside the pancreatic cells, including inside the beta cells that make insulin. In addition, once inside the pancreatic tissue the viruses triggered the production of inflammatory chemicals that are present in the autoimmune reaction. They also triggered the beta cell destruction that leads to type 1 diabetes.
This research doesn't prove that the flu virus causes diabetes, but it does suggest that there may be a link. Scientists think that cells in the immune system "present" bits of infected pancreatic tissue to a type of white blood cell known as a T-cell. Presentation is a normal activity in the immune system. It "teaches" T-cells to recognize that a virus or another organism is an enemy. However, researchers theorize that the T-cells are also "learning" to recognize the beta cells in the infected tissue and are treating these cells as enemies, too.
The process described above could only happen if the flu virus can enter the pancreas inside our bodies. Scientists say that this is possible. The virus normally stays in the respiratory system and the digestive tract, but it could travel up the duct that connects the pancreas to the duodenum (the first part of the small intestine). In addition, the virus sometimes enters the blood, which could then carry it to the pancreas.
Incidence of Type 1 Diabetes
Interestingly, doctors in some countries have noticed an increase in type 1 diabetes diagnosis after flu epidemics. The flu vaccine may therefore protect some people from this form of diabetes. Scientists say that even if only a relatively small number of people are likely to develop diabetes after a flu infection, the link between the two disorders could be significant. The incidence of type 1 diabetes is increasing by 3 to 5 percent each year. Researchers don't know why this is happening.
Dealing with Type 1 Diabetes
Why is the Incidence of Type 1 Diabetes Increasing?
The incidence of type 2 diabetes is increasing, but this is not unexpected. Obesity is a known risk factor for type 2 diabetes. The incidence of obesity is increasing in several countries. However, the incidence of type 1 diabetes is also increasing in many areas of the world. The increase has been too recent to be due to genetic changes in humans. (A genetic change across a whole species takes a long period of time.) Researchers think that there must be environmental factors that are causing the increased number of type 1 diabetes cases.
There have been several suggested causes for the increase in type 1 diabetes. The "hygiene hypothesis" is one proposal. This hypothesis says that in many countries young children are being protected from microbes to such a large extent that their immune systems aren't developing properly.
People with type 1 diabetes seem to be more likely to develop celiac disease, a condition in which the gluten present in certain grains destroys the villi on the lining of the small intestine. The villi are tiny folds that greatly increase the intestine's ability to absorb food. Most people today ingest far more gluten than people in the past. Some people have proposed that gluten is an environmental trigger for diabetes. An intolerance to cow's milk has also been proposed as a trigger.
Yet another suggestion is that obesity in children accelerates an autoimmune process that has already started and that it adds to the damage to the beta cells by forcing them to make too much insulin. Inadequate vitamin D levels in the body and exposure to toxins in pollutants have also been suggested as environmental triggers for type 1 diabetes.
Treating Type 1 Diabetes - How an Insulin Pump Works
An insulin pump is useful for diabetics because it can deliver insulin continuously. It has to be programmed and controlled by the patient based on their measured blood sugar level. A better device known as a bionic pancreas is being developed. This device measures blood sugar and delivers the correct amount of insulin automatically.
The Future For Diabetics
It's important that researchers discover the specific causes of type 1 diabetes, whatever they are. This discovery should help them find a cure for diabetes or help them find better treatments for the disease. Curing and treating any type of diabetes is important. It's especially important in type 1 diabetes, however, since this disease has the potential to affect people for a large proportion of their lives. If viruses are proven to be a cause, it may be possible to develop effective vaccines to prevent some cases of type 1 diabetes.
© 2012 Linda Crampton
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