A deadly strain of avian malaria has killed six of London Zoo’s penguins.
The disease is spread by mosquitoes, which have thrived in the wet and muggy summer.
Experts say that it is caused directly by a bite and cannot be passed on to humans.
The Zoo’s 58-strong colony of penguins are being kept under strict observation and are receiving anti-malarial drugs.
Keepers have installed mosquito traps and are also spraying lavender oil – a known mosquito deterrent - in the birds’ nests.
A London Zoo spokeswoman told the The Huffington Post UK: “Sadly, earlier this summer, six penguins died of avian malaria, which is a different strain to the one that infects humans and is endemic to the UK wild bird population.
"It can't be passed to humans and it can't be passed between birds, it only comes from a mosquito bite.
"It's something that we do routinely treat the penguins against. They're given a daily anti-malarial treatment in their breakfast, a tablet in their fish.
"We also spray lavender oil in their nest boxes and we've planted lavender around the enclosure, they're all natural deterrents for mosquitos and there are mosquito traps in the enclosure, as well.
"We continue to work very closely with the vets and all of our penguins appear healthy and well. No other birds in the zoo have been infected."
London Zoo opened in 1828 and is now home to 650 species, including 112 that are threatened in the wild.