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Melbourne, FL (Florida Today) -- More than 100 parasite-infested brown pelicans died in Brevard County in the past two months.

No one knows why.

"Thepelicans are emaciated and have heavy parasite counts, and, to ourknowledge, other bird species have not been affected," Dan Wolf, aresearcher with the Florida Fish and Wildlife Conservation Commission,said in a release.

Manyof the dead pelicans have turned up in Cocoa Beach. But others havebeen found on Merritt Island, in Melbourne, Indian Harbour Beach andalong the St. Sebastian River.

FWC researchers are assessing specimens from the pelican carcasses and the environment to identify a potential cause.

Theyalso sent samples two weeks ago to the U.S. Geological Survey'sNational Wildlife Health Center in Madison, Wisc. for testing. Butbiologists have yet to come up with definitive answers.

Researchersare awaiting results from additional samples sent this week that maydetermine whether the pelicans died of botulism, which sometimestriggers large bird die-offs.

But botulism generally kills birds quickly, Wolf said, leaving little time for the pelicans to become emaciated.

Birds get botulism when they eat rotten fish, which concentrate the Type E toxin produced by the bacterium Clostridium botulinum.Human botulism cases from Type E toxin are very rare. Type A or Type Bbotulinum toxin makes humans sick, usually after they eat spoiled cannedfood.

Botulism commonly kills ducks in western states. The Type E toxin can become concentrated in maggots.

Low and fluctuating water levels and warm temperatures can help trigger outbreaks.

"Wesuspect it may be botulism due to the warmer than average winter," SueSmall, director of the Florida Wildlife Hospital and Sanctuary in PalmShores, said earlier this week.

The hospital has seen at least 15 sick pelicans at the hospital in the past few weeks. All but two died.

Aroundthe same time last year, more than a dozen brown pelicans died in PalmShores, Rockledge and Indian Harbour Beach within about a month. Testsby FWC found a common bacteria at fault. The bacteria was most likelyfrom eating decomposed fish.

Ared tide has been lingering off Southwest Florida since September,killing a record 174 manatees so far this year. But no other significantfish kills, algae blooms or other toxic events that could kill birdshave been reported here.

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