Staff and regular visitors at Exmoor zoo in Devon been left heartbroken by the sudden death of a colony of 10 penguins following an outbreak of avian malaria.

The zoo announced that all of its Humboldt penguins, some of whom had been hand-reared, had died.

Hi everyone we have some very sad news that has taken us all here at the zoo a while to get used to. Today we... https://t.co/veByO6qoZJ — Beast at Exmoor Zoo (@exmoorzoo) September 26, 2016

There have been penguins at the zoo since it opened in 1982, and some of the penguins that died are the offspring of the original birds.

In a statement on Facebook, the zoo said the birds died two weeks ago but staff had been too upset to announce what had happened.

It said: “Exmoor zoo is greatly saddened to tell everyone that our penguins have all died from a quick and devastating outbreak of avian malaria.

“All the deaths occurred over a period of nine days and despite the best efforts of our veterinarian and the staff (some of whom have hand-reared the individuals from the day they have hatched) the outbreak could not be halted.

“Avian malaria can be carried by all wild birds and although is not infectious to us or the wild birds, penguins have never had to build an immunity to this as they live on or near the sea where the insects that carry the disease do not occur.

“This summer at least two other collections have also contracted the pathogen, which is a protozoa living in the blood of its hosts and usually spread by mosquitoes or biting midges from the original host bird.”

A penguin from Exmoor Zoo. Photograph: Exmoor Zoo

Danny Reynolds, the living collection manager at Exmoor zoo, said: “The protozoan pathogen cannot be easily identified in the blood of the penguins and dies very quickly so it cannot be seen with blood samples.

“Unfortunately, all drugs given from pathological reports had no effect and it is now known that once the malaria is contracted even the anti-malarial drugs cannot help the infected bird but the drugs can stop other penguins from contracting the disease.

“The problem for us was that our penguins were in summer moult, with skin exposed and typically do not feed well or regularly during this natural period of feather replacement which hid the symptoms”.

The zoo said it would consider whether to try to exhibit penguins again. Its statement added: “The disease may never strike again for another 25 years or more but could just as easily occur again next year – it all depends on what birds migrate through the avian malaria areas in Africa and if they visit Exmoor. If we do, then a lot of care will be given to any possible prophylactic treatments and stocks of the anti-malarial drugs will be available.”

It concludes: “Perhaps this is the time to say goodbye to some of the individuals we have looked after (some for 23 years or more) – Buster, Newquay, Ludo, Percy, Lemmy, Truddle, Owlie, Blossom, Friendly and Arthur. They are being keenly missed especially by those keepers who have given significant years to their care over time.”

Professionals and visitors expressed their sorrow on Facebook.

Paul Caine said: “Had to read that many times before believing it, I’m absolutely stunned ... My daughter, when she was about two years old, bought a fluffy penguin from the zoo and called it Buster. She’s now 10 and still completely inseparable from her Buster.”

It emerged last week that a number of Humboldt penguins died at Longleat Safari Park in Wiltshire.