>>> FORMER TOP U.S. INFECTIOUS DISEASE OFFICIAL DR. ANTHONY FAUCI IS RECOVERING AT HOME FROM A WEST NILE INFECTION. DR. MAX OUT SHE WAS HOSPITALIZED FOR NEARLY A WEEK AFTER CONTRACTING THE VIRUS. >> Reporter: WEST NILE INFECTIONS ARE THE LEADING CAUSE OF FETAL BORNE DISEASE IN THE UNITED STATES. MANY AREAS ARE SEEING CASES INCLUDING NEW YORK CITY WHERE THE HEALTH DEPARTMENT IS SPRING FROM DUSK TO DAWN. FORMER HEALTH OFFICIAL DR. ANTHONY FAUCI IS RECOVERING AT HOME AFTER BEING HOSPITALIZED WITH AN INFECTION. CBS'S CHIEF MEDICAL CORRESPONDENT SPOKE WITH DR. McNULTY OVER THE WEEKEND WHO SAID AN INFECTED MOSQUITO PROBABLY BID HIM IN HIS BACKYARD. >> ABOUT TWO WEEKS BEFORE THAT HE STARTED TO NOT FEEL VERY WELL. MOSTLY FATIGUE. HE DEVELOPED SHAKING CHILLS, FEVER, AND HE WAS HOSPITALIZED FOR ABOUT A WEEK. >> Reporter: PEOPLE AT RISK INCLUDE THE ELDERLY AND PEOPLE WHO ARE IMMUNOCOMPROMISED. WEST NILE INFECTIONS CAUSE NO SYMPTOMS IN MOST PEOPLE, THAT OTHERS CAN DEVELOP FEVERS, BODY ACHES, JOINT PAIN AND A RASH. >> ABOUT 1-150 PEOPLE WHO GET INFECTED GET A MORE SERIOUS FORM THAT INVOLVES THE CENTRAL NERVOUS SYSTEM. THE MEMBRANE THAT LINES THE SPINAL CORD, THAT IS A MUCH MORE SERIOUS SITUATION. >> Reporter: SO FAR THIS YEAR MORE THAN 250 CASES HAVE BEEN REPORTED IN MORE THAN 30 STATES. >> IT IS A MOSQUITO BORNE ILLNESS. WEAR CLOTHING THAT COVERS YOUR SKIN. YOU CAN HAVE INSECT REPELLENT. GET RID OF STANDING WATER. STANDING WATER IS WHERE MOSQUITOES CAN MULTIPLY AND READ. >> Reporter: THE CDC SAYS THERE IS NO TREATMENT. REST, FLUIDS AND PAIN MEDICATIONS MAY HELP ALLEVIATE SYMPTOMS. JARRED HILL, CBS NEWS, NEW YORK. >>> INVOLUNTARY EVENING LOCKDOWN IS ISSUED IN PARTS OF MASSACHUSETTS BECAUSE OF A POTENTIALLY FATAL MOSQUITO BORNE DISEASE