Rabies. For humans, it's a killer. And for pets, it's just as fatal. With more than 40 confirmed cases of rabies across the state this year, including an outbreak in Pinal County, officials are urging people to take extra caution and vaccinate their pets.

Click on the graphic to see how rabies is spread

Three students at Higley High School in Gilbert are being treated for rabies exposure after an infected bat was found on campus April 11. Bats recovered in Queen Creek and Scottsdale last week also tested positive for rabies.

However, state and local health officials are more concerned about the number of rabid animals found in Pinal County. This year, there have been nine confirmed cases, more than last year's total of seven and tying 2006's high.

The flare-up prompted the Pinal County Public Health Services District to issue a rabies health advisory this month.

While human exposures have been limited, officials are worried because the disease is fatal to humans once symptoms occur.

"Even if the symptoms are mild, it's already too late," said Dr. Elisabeth Lawaczeck, Arizona Department of Health Services veterinarian.

The disease is less deadly for household pets. However, it's very expensive to treat.

Even if a pet is exposed but doesn't contract rabies, state law requires the pet be placed in quarantine for six months at the owner's expense, said Tom Schryer, county Public Health director.

Most people cannot afford the costs, forcing many to euthanize their pets.

Protecting cats and dogs from rabies only requires a vaccination, usually costing less than $10.

Rabies is an infectious disease that inflames the nervous system, including the brain and spinal cord. It's caused by a virus present in the saliva of infected animals.

Once contracted, rabies begins with symptoms such as headaches and numbness, but quickly escalates. In a few weeks, victims move from muscle spasms to loss of body control, delirium, coma and eventually death.

Wild creatures such as bats, skunks, foxes, raccoons, bobcats and coyotes are the most common rabies-carrying animals in Arizona. Unlike other states, Arizona rodents such as rats, mice and squirrels are not known to carry the disease.

Officials said it's common to see a surge in rabies cases in certain areas such as Pinal County every couple of years.

"It's like a cycle," Lawaczeck said. The cases also can spike in spring and fall months, she said.

Domestic animals such as cats and dogs are less likely catch rabies.

But in 2007, more than 75 domestic pets were exposed to rabies, the Arizona Department of Health Services found.

There also were 55 human exposures last year, and health officials have confirmed 20 this year.

However, no person has contracted the disease.

The last confirmed case of human rabies in Arizona was in 1981. That person died.

"It's probably the most fatal disease known to man," Lawaczeck said.

It's more than 99 percent fatal, and there have only been six confirmed survivors of rabies in history.

But not to worry, officials say, because human cases of rabies are rare. And only about two to three people contract rabies in the United States each year.

Rabies can incubate in humans in as short as a few days, and up to seven years. The normal time: four to 12 weeks.

If treatment is started right after exposure, survival is 100 percent. The normal course of rabies treatment is a series of five shots given over about a month.

The number of human cases of rabies has decreased steadily throughout the years.

But exposures are still a major concern, especially in the area surrounding the Valley as the population pushes out into former wildlife areas, Lawaczeck said.

For this reason, experts advise people to steer clear of wildlife and decrease things that may attract wild animals to themselves or their homes.

However, if people do come across a wild animal, experts said there are clear ways to recognize rabid animals.

On Thursday, two separate hikers were attacked by a rabid fox in the Boynton Canyon area, near Flagstaff. In both situations, the fox charged at the men from out of the woods. One of the hikers had to pry the fox off his leg with a stick and used a rope to tie it to a tree until animal control officials arrived.

Nocturnal animals, such as bats, foxes and skunks, coming out in the day is a common sign of rabies.