A tick-borne infection known as Babesiosis, which can cause severe disease and even death, is becoming a growing threat to the U.S. blood supply, government researchers said on Monday.

There are currently no diagnostic tests approved by the U.S. Food and Drug Administration that can detect the infection before people donate blood.

A 31-year study by the Centers for Disease Control and Prevention now suggests the parasitic infection may be increasing.

Babesia infections are marked by anemia, fever, chills and fatigue, but they can also cause organ failure and death.

The still rare disease is known to occur in seven U.S. states in the Northeast and Upper Midwest in the spring and summer.

But a study led by Dr. Barbara Herwaldt of the CDC, published in the Annals of Internal Medicine, found cases had occurred year-round and in states where Babesia parasites are not found -- including as far away as Texas and Florida.

States in which the parasite occurs naturally are Massachusetts, New York, Connecticut, Minnesota, Rhode Island, New Jersey and Wisconsin.

Of the 162 cases of Babesia infection caused by blood transfusions between 1979 and 2009, nearly 80 percent occurred between 2000 and 2009.

Babesia microti has become the most frequently reported transfusion-transmitted parasite in the United States, CDC researchers wrote, far outpacing malaria infections, which accounted for 49 cases of transfusion-associated disease during the same period, including just five cases during 2000-2009.

Premature infants appear to be especially vulnerable.

A separate study published on Monday in the journal Pediatrics by a team at the University of Nebraska looked at seven cases of transfusion-associated Babesiosis in premature infants.

They found blood transfusions from two infected units of blood caused all seven of the cases of Babesiosis.

Symptoms of the infections varied widely, but babies with the lowest weights at birth were at greatest risk of serious infection.

The authors warned doctors in areas in which Babesiosis occurs to be watchful for cases in premature infants exposed to blood transfusions.

The CDC researchers called for better ways to prevent and detect cases of transfusion-associated Babesiosis.

Our findings underscore the year-round vulnerability of the U.S. blood supply -- especially, but not only -- in and near Babesiosis-endemic areas.

They also highlight the importance of multi-agency collaborative efforts to detect, investigate, and document transfusion cases; to assess the risks for transfusion transmission; and, thereby, to inform the scope of prevention measures.

To deter transfusion-linked Babesiosis, the CDC in January said public health departments should report all cases of the infections to the CDC.

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