An outbreak of anthrax has killed at least 30 hippopotamus in South Africa's famed Kruger National Park wildlife reserve, the country's parks authority said Tuesday.

Officials believe the deaths are linked to a flare-up of the highly infectious disease in the giant park which has killed 45 roan antelope since August.

"Vultures or blowflies could have eaten the flesh of the roan antelope and then went to drink, and that is how the hippos contracted anthrax. That's the theory at present," said South African National Parks (SANParks) spokesman Ike Phaahla.

Post mortems of 30 hippo carcasses have been linked to the bacterial disease, which can also be fatal to humans. Six more dead animals were found at the weekend and are being examined.

"Gradually we've been finding them," Phaahla said.

Kruger is home to Africa's "Big Five" -- rhino, lion, elephant, leopard and Cape Buffalo.

Animals such as lions could be affected if they eat the contaminated flesh of dead animals.

"Obviously we are worried about" other species, Phaahla said.

Anthrax outbreaks naturally occur, usually in the dry season, in the northern part of the park, which has seen eight major flare-ups since 1960. Some 2,000 animals died in 2010.

Vultures are immune to anthrax but spread the disease by eating infected dead animals and then defecating in water where they drink or bathe.

Outbreaks are linked to high population densities, according to SANParks. Previous outbreaks have seen the disease naturally tail off after the arrival of rains and when animal numbers are lower.