( CNN ) -- An estimated 40,000 people in the United States are involved in professional dogfighting , an illegal blood sport with fight purses as high as $ 100,000 . The latest accusations against Atlanta Falcons quarterback Michael Vick and three other people highlight the problem . They are accused in an indictment that describes dogs being routinely executed if they did n't fight fiercely . The indictment was handed down Tuesday by a federal grand jury in Richmond , Virginia . The nightmare of dogfighting is growing , according to the Humane Society of the United States . John Goodwin , an expert on animal fighting with the Humane Society , says there are an estimated 40,000 professional dogfighters in the United States , involved in putting on fights and buying and selling fighting dogs . Watch what goes on at a high-stakes dog fight » . But , Goodwin adds , there could be as many as 100,000 additional people involved in `` streetfighting '' -- informal dogfighting , often involving young people in gangs . `` It 's far more pervasive than people think and it 's definitely been on the upswing in the past five to 10 years , '' he told CNN . See how dogfighters operate and have their own language » . Statistics from animal shelters give another indicator of the rise in dogfighting , Goodwin said . Fifteen years ago , 2 to 3 percent of the dogs coming into animal shelters were pit bulls ; now , he said , pit bulls make up about a third . At one shelter in Jersey City , New Jersey , Goodwin said , the figure is 65 percent , with 20 percent of them showing the scars that indicate they have been fighting dogs . A database run by animal advocacy group Pet-abuse.com , which collects reports of animal abuse , shows reports of dogfighting cases increased from 16 in 2000 to 127 in 2006 . The group has found 74 cases reported so far this year . Dogfighting is illegal in all 50 states . It 's a misdemeanor in Idaho and Wyoming , and a felony everywhere else . But in some states where dogfighting is a felony , it 's still perfectly legal to own a fighting dog or be a spectator at a dogfight . See where it 's legal to be a spectator » . A bill signed by President Bush in May made the federal law against dogfighting tougher , by strengthening penalties to felony level . The law bans interstate commerce , import and export related to animal fighting activities . Violators can now be sentenced to three years in jail and a $ 250,000 fine . Previously the maximum sentence was a year in jail . Despite the laws , dogfighting is big business . Goodwin said it 's impossible to estimate the amount of money involved , but the purse for a top-level professional fight could be $ 100,000 . `` There are about a dozen underground dogfighting magazines , and about half a dozen ... registries that are exclusively used by either dogfighters or people that are fighting dog enthusiasts , '' Goodwin said . `` You have an organized infrastructure for what is a criminal industry . '' E-mail to a friend .
Humane Society estimates 40,000 `` professional '' dog fighters in U.S. Official says there could be an additional 100,000 `` street '' dog fighters . Purses at top-level dogfights may be $ 100,000 . Dogfighting a felony in 48 states , a misdemeanor in Idaho and Wyoming .