Two hundred surgical patients are being recalled for blood tests after a patient who went into hospital for a hip replacement contracted malaria.

Bedford Hospital, which attracted criticism last year for storing corpses in its chapel of rest, has asked patients operated on as far back as December to be tested to find out whether one of them or a member of staff has passed on the blood-borne parasite that causes the illness. It is thought unlikely, though not impossible, that it was transmitted by a mosquito.

Senior sources at the hospital said the pensioner who fell ill with malaria this week had rarely, if ever, been abroad and had never visited malarial regions. He is understood to have been transferred to Addenbrooke's Hospital in Cambridge where, although seriously ill, he is responding to treatment.

There have been only four cases in the world of human-to-human transmission in hospitals in the past 20 years. Three years ago, three people in Nottingham were infected through use of the same saline drip.

Dr Pat Nair, consultant in communicable disease control, at Bedfordshire health authority, said: "We are looking at all possibilities, patient to patient, staff to patient and mosquito to patient, although we do not thing the latter is possible because we do not have that kind of mosquito in Bedford. It is in other parts of the country, usually near airports. But we are not, so that is unlikely. The hospital is the most likely source of the infection.

"The incubation period is seven days to three months but usually within the first two weeks, so we have written to all surgical patients, starting with those who were operated on on a certain wing two weeks before this man displayed the symptoms. Staff are also being tested, but at the moment it is like looking for a needle in a haystack." Dr Nair would not say which wing was affected.

Sources told The Independent that a temporary member of staff who had worked in west Africa was being considered as a potential source. He is said to have told other staff that he had malaria. .The hospital said last night that no one had been suspended, but a spokeswoman could not say whether that was because the staff member's contract had already ended.

One consultant said: "It really is unbelievable to think that you go into hospital for a hip replacement and come out with malaria. If this person is found to be the source, questions have to be asked as to whether the hospital knew he had malaria and why he was allowed to come into contact with surgical patients."

Dr Jeremy Saunders, Bedford Hospital's medical director, confirmed that a full investigation was under way.

The lifecycle of the malaria parasite normally relies on the Anopheles mosquito in whose stomach it develops from an asexual to a sexual form, ready to be passed through the insect's salivary glands into a human. Once in the bloodstream, it travels to the liver where it attacks red blood cells and multiplies to the point where the blood cells burst and release spores.

In rare cases, however, it can be passed from person to person through blood contact. When this happens, the parasite apparently manages to bypass the mosquito stage.