The little-known blood infection called sepsis kills about 200,000 Americans each year, and the body’s own immune system does the deed.

As with Lisa Strong and Brazilian beauty queen Mariana Bridi da Costa, who died Saturday, sepsis can develop when any type of infection in the body invades the bloodstream, where it can take over the body and threaten death.

The invaders often are bacteria or viruses from pneumonia, skin abscesses, meningitis or internal infections. In Brida da Costa’s case, it was a urinary tract infection. The elderly, infants and people with chronic disease or weak immune systems are most at risk.

The immune system goes on high alert, sending out legions of antibodies to kill the attackers. The result: inflammation, fever, rapid heart rate and rapid breathing. In healthy people, the body wins.

But sometimes the battle itself causes collateral damage. In sepsis, or septicemia, small blood clots can develop that block blood flow, threatening heart attack or stroke. The blood may fill with so many attacker toxins and antibodies that blood pressure drops dangerously low, a condition called septic shock. If treatment doesn’t work, organs can fail.

Overall, 85 percent of sepsis patients recover. But in septic shock, 45 percent to 60 percent die.

Many cases cannot be prevented, but the best protections are: Wash hands often. Get immunizations. Seek prompt care for infections, especially in babies. Alert your doctor about redness, swelling or pus near broken skin.

Davie woman, Brazilian beauty queen both victims of septic shock