Two more penguins have died at the Calgary Zoo bringing the total number of deaths up to four so far this year.

A three-year-old Humboldt penguin named Eduardo died on Sunday after picking up a fungal infection that affected his respiratory system.

“The post-mortem examination showed advanced and severe infection to his left air sacs and left lung, while his right side was normal,” said senior veterinarian Dr. Doug Whiteside.

“Owing to a bird’s very efficient respiratory system and also because animals are so adept at hiding that they are not feeling well, unfortunately by the time Eduardo demonstrated signs of illness, his disease was far too advanced for treatment to be effective.”

The fungal infection, called Aspergillosis, is one of the most common causes of death in both captive and wild penguins.

A Gentoo penguin Akemi also died of heart failure on Monday after getting avian malaria. The three-year-old bird had been treated for a bumblefoot infection in the past.

The parasite is the second biggest killer of penguins in captivity. It is not a threat to humans as mosquitoes carrying the malaria and the parasites are species-specific.

“One week ago Akemi’s blood showed no evidence of malaria; however, the parasite was detected in the red blood cells yesterday,” explained Dr. Whiteside.

“Like the two Humboldt penguins we lost in August, Akemi became ill suddenly and died within a very short period of time — less than 48 hours. However, she is the first penguin where we have been able to demonstrate the parasite in red blood cells.”

Zoo officials said in August the cause of two penguin deaths could be from an infection caused by the bacterium Chlamydophila psittaci.

“It seems clear that there may well be an association between Akemi’s death and the two Humboldt deaths in August as they all shared the outdoor exhibit. And with our wet and then hot summer, were likely exposed to a greater number of mosquitoes carrying the parasite compared to ... the previous year ” concluded Whiteside.

“We are still waiting for advanced parasitological tests to come back from a lab in the U.S. for the two Humboldts, which would confirm a connection.”