An Overview of Astrovirus

Astroviruses are a type of virus that causes diarrheal illness (gastroenteritis). Infants and young children are most likely to have diarrhea caused by astroviruses, but the infection also occurs in the elderly and those with compromised immune systems.

Although it can cause symptoms similar to other common viral infections, diarrheal illness from an astrovirus infection is generally much less severe than those caused by rotavirus and norovirus. It also rarely requires any medical treatment.

However, researchers are still learning about human astroviruses. Our knowledge of how they work is still new compared to other viruses that cause similar illnesses.

Astroviruses are one of several pathogens that can cause gastroenteritis in humans. The main symptom caused by astrovirus is diarrhea. Compared to other microorganisms that can cause gastroenteritis, such as rotavirus and norovirus, diarrhea caused by astrovirus is usually mild.

While mild diarrhea is the main symptom astroviruses cause, a person who gets sick may also have other common symptoms of gastroenteritis, including:

• Nausea
• Vomiting
• Stomach ache
• Loss of appetite
• Body aches
• Fever

Babies, very young children, the elderly, and people with compromised immune systems (such as those being treated for cancer or living with HIV) are more likely to become dehydrated.

Healthy people with an intact immune system generally recover from an astrovirus infection in a few days. In some cases, they may not even know they have been infected by an astrovirus because they are otherwise asymptomatic (without symptoms).

A person who is infected but is not showing symptoms (referred to as a "carrier") is still able to spread the virus to others.

Astroviruses get their name from their star-like appearance when viewed under a microscope. There are several different kinds of astrovirus, some of which infect humans. The virus has also been found in other animals including dogs, birds, pigs, cows, bats, and even dolphins.

Astroviruses tend to circulate more frequently during specific seasons. In parts of the world with temperate climates, astrovirus infections occur more frequently in the winter and spring. In tropical climates, astrovirus is more common during the rainy season.

However, astroviruses are present year-round and can make people sick at any time, especially in places where sanitation is poor or people live in crowded spaces.

Infants and children under two are most likely to have a diarrheal illness caused by astroviruses. While it is less common than rotavirus and other diarrhea-causing viruses, astroviruses account for 2% to 9% of all pediatric gastroenteritis cases in the world.

Astrovirus is very small, and it only takes a few viral particles to make a person sick. Once a person is infected with astrovirus, viral particles will continuously be shed into fecal matter. Even after the person starts to feel better, they may still be shedding particles, allowing for the fecal-oral transmission of the virus.

Most children will develop an immunity to astroviruses by the time they reach 10 years of age. This protection is why astroviruses do not usually make adults sick. However, it is believed that immunity wanes over time, which is why elderly people are more likely to get sick from the virus.

In addition, malnutrition is a significant risk factor for astrovirus infection in both children and the elderly.

Astrovirus can usually be diagnosed with a combination of a physical exam, a review of your medical history, and various blood and stool tests. Based on a review of your symptoms and risk factors, your doctor may decide to treat you presumptively if the symptoms are mild.

In other cases, your doctor may order a battery of tests to identify the specific cause of diarrhea, especially if the symptoms are severe or there is a local outbreak of diarrheal disease. The tests may include:

• Stool culture to visually ad chemically test for astrovirus inn a stool sample
• Enzyme-linked immunosorbent assay (EIA), a blood test that checks for immune proteins, called antibodies, that the body produces in response to infectious microorganisms
• Polymerase chain reaction (PCR) tests able to detect astrovirus RNA in blood

The results of the tests can usually be returned in one to three days. A positive result means that you have been infected with astrovirus. A negative result means that you have not.

Viral gastroenteritis can be caused by several pathogens. In some cases, it is possible to be infected by more than one virus at the same time (called a coinfection).

An illness caused by a virus cannot be treated with antibiotics. Therefore, any treatment is prescribed for viral gastroenteritis would be supportive and focused o the management of symptoms (such as the alleviation of nausea or fluid replacement for dehydration).

With that said, scientists have made significant advances in the development of neutralizing monoclonal antibodies that may one day effectively prevent or treat astrovirus infections.

Until such an intervention is found, the only thing you can do to avoid getting or spreading astrovirus is to follow certain common-sense prevention rules. These involve:

• Proper handwashing, especially after using the bathroom
• Not sharing utensils or cups if you or people around you are sick
• Staying home from work or school if you are sick
• Avoiding the handling and preparation of food when sick or while recovering from illness
• Using antiseptic or disinfectants to clean surfaces, especially in the bathroom and kitchen

Astroviruses are one of several viruses known to cause gastroenteritis. While most infections are mild, extra care should be taken to avoid infection in people who are at greatest risk of complications, such as infants, the elderly, or those with advanced HIV infection. Improved hygiene and sanitary practices, along with improved nutrition, will go a long way to prevent astrovirus infection in these vulnerable individuals.