Dear Doctor: What is rat bite fever? Just how contagious or dangerous is it? I read that a 10-year-old boy died from it after being bitten by his pet rat.

Dear Reader: Yes, that was a tragic story. A rat purchased from a pet store transmitted a bacterial infection known as rat bite fever to a young boy who later died. Although the details caused the incident to get wide media play -- we tend to think of rats as vermin rather than pets -- the Centers for Disease Control and Prevention say that rat bite fever in the United States is quite rare.

Rats have been identified as carriers of disease for thousands of years. Rat scratches, urine and feces are all potential pathways for illness. Add in the various pests and parasites that live off rats and themselves spread disease -- think fleas and the bubonic plague, which killed 50 million people in Europe in the 14th century -- and it's no surprise that these rodents have earned a bad reputation.

So what is rat bite fever? It's a full-body illness with symptoms including fever, chills, body aches, headache and vomiting. In many patients, a rash made up of either flat or raised red bumps may appear a few days after the onset of fever. In the U.S., the cause of the disease is usually a bacterium called Streptobacillus moniliformis, which is transmitted through contact with the infected rat's saliva or urine. Spirillum minus, which also causes the disease, is more commonly found in Asia.

Although rats are the main carriers, the bacteria can be present in mice and gerbils as well. Rat bite fever is fatal in about 10 percent of infected persons who go untreated. In the case of that young boy, he may have been bitten by the rat, or may have become infected through handling his pet. As to your question about whether it's contagious, there have been no reports of rat bite fever being transmitted between humans.

The bacterium is present in healthy rats, both wild and domesticated. That means it's found in lab rats, too, which puts researchers at risk. But rat bite fever tends to be most common in urban areas, where rats can easily find food and shelter, and where residents have little control over coming into contact with the rodents or their urine.

Since a single test to diagnose the disease doesn't exist, the diagnosis must be made by identifying the presence of the bacteria in blood, skin or in the fluid of the joints of lymph nodes. However, prompt treatment is important, so the CDC recommends that patients who develop the cluster of symptoms associated with rat bite fever, particularly if they occur within two days to three weeks after contact with a rat, receive a course of antibiotics. Penicillin works extremely well, and for those who are allergic, other antibiotics are also effective.

We're very happy to be able to leave you with some good news: With timely treatment, the vast majority of patients with rat bite fever recover fully.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I've been reading a lot of warnings about the recent wet weather causing an abundance of ticks and their potential to cause disease. I knew about Lyme disease, but now Powassan virus? What's that? And just how dangerous are ticks?

Dear Reader: Ticks are external parasites that, because they feed on blood, are quite efficient at transmitting disease. In each of the three life stages that a tick goes through after hatching, it needs blood to survive. Depending on the species, ticks will feed on mammals (that's us), birds, reptiles and amphibians.

A variety of ticks throughout the United States can transmit more than a dozen dangerous and sometimes deadly diseases. These include Lyme disease, Rocky Mountain spotted fever, tularemia, and Colorado tick fever, to name a few of the most commonly known. The tick picks up the disease while feeding on an infected host, and then can transmit it through its saliva during future feedings.

One of the lesser-known diseases is Powassan virus, a flulike illness that can cause inflammation in the brain. It is spread by several types of ticks found in the northeastern states and in the Great Lakes region. The disease is fatal in up to 15 percent of individuals who show symptoms. About half of those who survive face ongoing neurological difficulties.

Powassan virus was once rare, with about two reported cases per year between 1950 and the early 2000s. That number has risen to 75 reported cases in the last decade, or close to eight per year. Some experts believe this may be due to increased awareness in diagnosing the disease.

However, Lyme disease, with close to 30,000 confirmed cases each year, remains the most common tick-borne illness in the U.S. According to the Centers for Disease Control and Prevention, the total may actually be as high as 300,000 infected individuals per year, when unconfirmed cases are factored in.

While there are some species of ticks that don't carry disease, without specialized knowledge it's almost impossible to tell them apart from those that do. As a result, the best advice is to protect yourself, your family and your pets against all tick bites.

Ticks prefer areas that are moist and humid, and concentrate in wooded and grassy areas. They can't jump or fly, so they perch at the tips of grasses and shrubs, where they can easily attach to a host as it brushes by.

To avoid tick bites:

-- When in grassy or brushy areas, wear long sleeves, long pants and close-toed shoes. Tuck pants into socks. Light-colored clothing makes spotting ticks easier.

-- Insect repellents that contain 20 percent DEET may be helpful. Some experts say picaridin is even better. Reapply according to manufacturer instructions.

-- Treat clothing, boots and tents with products containing 0.5 percent permethrin, which stays effective through several washings. Pre-treated clothing and gear is also available and may offer longer protection.

-- After spending time outdoors, be sure to do a tick check. Visually scan all areas of your body, including your scalp and hair.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I know that as far as medical problems go, eye "floaters" are pretty minor. But I've just noticed some new ones, and they're really annoying. What are they? Is there any way to get rid of them?

Dear Reader: Floaters are those tiny specks, strands or cobwebs that drift across your field of vision. Try to look right at them and they'll skitter away. Move your eyes away from them and they'll follow. Hold your gaze still and they'll gently float about, which is the trait that gives them their name.

Floaters develop in the vitreous -- the clear, gel-like fluid that fills the space between the lens at the front of the eye and the retina at the rear. It's composed mostly of water, with a small amount of collagen, other proteins, salts and sugars. The job of the vitreous is to protect the delicate structures of the eye, support the eyeball's spherical shape and hold the light-sensitive cells of the retina in place.

Although people of any age can develop floaters, they do tend to be more common in adults 40 and over. That's because as we age, the vitreous gradually softens and shrinks. Portions of the collagen can become stringy, and the other proteins dissolved in the vitreous form tiny clumps. As these bits and strands float in the jelly-like vitreous, they cast shadows on the retina. The retina then sends this information to the brain via the optical nerve. The result is a visual image of the changes taking place within our eyes.

For the most part, the presence of floaters is a normal part of aging. However, if the number of floaters suddenly increases, and if the increase is accompanied by flashes of light within the field of vision, it's time to check in with your eye doctor. These can be the signs of more serious problems.

We understand your frustration with floaters -- no matter where you look, there they are. However, at this time, there are no good solutions for dealing with them. For those (extremely) rare individuals for whom floaters are so numerous that they interfere with vision, treatment options do exist.

One choice, which is rarely used, is laser therapy. In this approach, an ophthalmologist targets the floaters with a special laser. The idea is that the energy of the radiation will break up the floaters so they become less visible. The risk is that the laser can cause damage to the retina.

The other option is a surgical procedure known as a vitrectomy. The vitreous -- along with all the floaters -- is removed via an incision, and is replaced with a saline solution. This also carries serious risk. Complications include retinal detachment, retinal tears and cataracts.

Do-it-yourself approaches to dealing with floaters, which, unfortunately, don't have much effect, range from harmless (eye exercises, eating more blueberries or broccoli) to potentially dangerous. Your eyesight is far too precious to risk, so don't try anything without checking with your doctor first.

Given time, your brain will tag floaters as unimportant information and, for the most part, will let you forget them.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)