intro: As bacteria and other pests evolve to evade medications, infections that were once easily cured with a few pills or creams can become chronic or even deadly.
According to Dr. Margaret Chan, director general of the World Health Organization, "Things as common as strep throat or a child's scratched knee could once again kill."
The most worrisome development for experts is the rise of bacteria immune to normal antibiotics.
"We are losing our first-line antimicrobials," Chan said in her keynote address at the conference on combating antimicrobial resistance in 2012. "Replacement treatments are more costly, more toxic, need much longer durations of treatment, and may require treatment in intensive care units."
Other organisms have also evolved to evade human remedies.
Pests such as lice are becoming nagging problems as well, as they produce stronger eggs and become resistant to the old medications that have usually kept them in check.
Approximately 12 million American children become infected with the tiny pests each year.
With mutant bugs and bacteria on the loose, ABC News asked infectious disease experts which superbugs pose the biggest threats.
quicklist: 1 category: Risky Superbugs title: The Latest Head-Scratcher url: text:In schools across the country, kids are becoming infected with a new breed of "super lice." The little pests have developed harder exo-skeletons and lay eggs at different times, so they are not easily killed by the over-the-counter lice shampoo.
"They call it 'super' lice, because it's kind of like antibiotics to humans when a product is misused," said Maria Botham, owner of the Hair Fairies, a children's hair salon for lice removal. "[When] overused on a bug. You're building up a pretty strong bug, hence 'super' lice."
As lice become more "immune" to normal lice shampoos, parents are turning to experts, such as Botham, who pick the lice from hair by hand for a very high price.
A session at the Hair Fairies costs about $300.
quicklist: 2 category: Risky Superbugs title: The Original Superbug: Staphylococcus Aureus url: text: Almost everyone's heard of MRSA, or methicillin-resistant Staphylococcus aureus. But few people understand just how pervasive the original superbug has become.
Roughly one in 50 people carries a strain of staph resistant to common antibiotics, according to the National Institutes of Health. If the bug invades a wound, it can cause an infection that's minor and localized, as in a pimple, or serious and widespread, involving the heart, lungs, blood and bones.
"MRSA continues to be the biggest threat because it could become more widespread," said Dr. William Schaffner, chairman of prevention at Vanderbilt University Medical Center.
MRSA infections usually strike elderly hospital inpatients or nursing home residents. But the number of MRSA cases out in the community is on the rise, according to the NIH. It can spread among people working out at the gym through contaminated towels or equipment, and has even been passed among children at day care facilities.
quicklist: 3 category: Risky Superbugs title: The Hospital Lurkers: Clostridium Difficile and Acinetobacter url: text: Doctors have long been battling a group of six hospital-borne pathogens dubbed Eskape: Enterococcus, Staphylococcus, Klebsiella, Acinetobacter, Pseudomonas and Enterobacter. Now those six bugs are escaping antibiotics.
"These organisms were present in hospitals 20 years ago," said Dr. John Bartlett, chief of infectious diseases at Johns Hopkins University School of Medicine in Baltimore. "Now we've used so many antibiotics to treat them, they've been trained to become resistant."
The bacteria invade vulnerable bodies through hospital equipment, such as surgical implants and central lines.
"When people come into the hospital, they often get metal put in them, or plastic lines. All those foreign bodies become susceptible to infection," said Bartlett. "We can't help it. It's nobody's fault."
quicklist: 4 category: Risky Superbugs title: The Foodborne Bugs: Escherichia Coli and Salmonella url: text: The bacteria behind food poisoning are becoming drug resistant, partly because farm animals are fed antibiotics to promote growth.
"Eighty percent of antibiotics in the U.S. are given to animals, not people," said Bartlett. "Now we're tracing some of these antibiotic resistant infections back to the farm."
Earlier this month, the U.S. Centers for Disease Control and Prevention reported that drug-resistant strains of E. coli causing urinary tract infections in women could be traced back to chickens fed antibiotics.
"E. coli is the most common cause of simple urinary tract infections, which we can very quickly and easily treat today. But as it becomes resistant, what was once simple [to treat] will become complicated," said Schaffner.
The European Union has banned antibiotics as growth-promoters. But the United States continues to lag behind, only recently restricting the use of antibiotics called cephalosporins in livestock.
"Quite frankly, I think that's embarrassing," said Bartlett. "Nobody's talking about the U.S. being very aggressive or successful in dealing with this problem."
A federal court judge ruled Thursday that the U.S. government must take steps to ban the use of penicillin and tetracycline -- antibiotics used to treat pneumonia, strep throat and urinary tract infections in humans -- in animals.
quicklist: 5 category: Risky Superbugs title: The Sexually Transmitted Infections: Gonorrhea and Chlamydia url: text: Super gonorrhea may sound funny, but it's no joke. Antibiotic resistance means sexually transmitted infections once cured with a few pills could require treatments that are more invasive.
"We might have to rely on intravenous or intramuscular treatments, meaning the patient would have to come in or someone would have to go to their home," said Schaffner. "These people don't want to be recognized in their home environment as having one of these infections, which a visit would kind of announce. So people will begin avoiding treatment. You have a spiraling series of problems."
quicklist: 6 category: Risky Superbugs title: The Global Threat: Tuberculosis url: text: Tuberculosis kills 1.34 million people each year worldwide. And now the disease, once curable with antibiotics, is becoming resistant to multiple drugs.
"Among the world's 12 million cases of tuberculosis in 2010, WHO estimates that 650,000 involved multidrug-resistant TB strains," WHO's Chan said in her keynote address. Chan added that treating multidrug-resistant TB is extremely complicated, "typically requiring two years of medication with toxic and expensive medicines, some of which are in constant short supply. Even with the best of care, only slightly more than 50 percent of these patients will be cured," she said.
Although most cases of multidrug resistant TB are in developing countries, there were 92 U.S. cases reported in 2011, according to WHO data.
"We live in a very small world today," said Schaffner, explaining how travelers can import antibiotic resistant bacteria from developing countries. "It's a very small word and the bacteria do not need passports."