BACK in 2016 I highlighted in this very column an ornithological mystery that had all the scientists baffled. What was causing the disappearance of our familiar house sparrow from many towns and cities around the country could not be found. The Independent newspaper even offered a £5,000 reward to anyone who could come up with a definitive explanation.

Well, this summer brings news which could result in the money finally being claimed. A team of scientists from the ZSL Institute of Zoology, in collaboration with the RSPB and British Trust for Ornithology, decided to look into whether disease might be a factor in the loss of the “cockney sparrer” and they did indeed find a link.

The disease in question, however, has taken most people by surprise – I for one was flabbergasted to hear that it was malaria that was killing our garden birds.

Actually, this is too simplistic an explanation; what the scientists think is happening is that malaria is weakening young birds sufficiently for them to not survive the hardships of their first winter.

As so often happens in investigations such as this one, the results have raised as many questions as they have provided answers. Why, for instance, is it only urban sparrows that are succumbing to malaria – and why is it particularly bad in London?

Certainly, up here in Ryedale there has been no noticeable recent decline in our house sparrow populations. This summer, cheerfully chirruping flocks have filled the hedgerows around my home village and they remain the most frequent visitors to the bird feeders in our garden.

Friends in the, admittedly small, towns of Pickering and Malton also report healthy numbers of house sparrows on their patch as well. It would be interesting to know what proportion of our local sparrows, if any, are carrying the malaria parasite.

Most folk are aware that malaria is a blood disease caused by a protozoan called Plasmodium which is transmitted between hosts by biting insects, notably mosquitoes, and you may well be wondering like I did, whether a pesky mosquito could bite one of us after biting a sparrow and pass the disease on.

Fortunately for us the bird malaria microbe is Plasmodium reticulum which is not able to live inside human bodies so we are safe from cross-infection in this case.

Before you get too relaxed about the situation, though, here are some interesting facts about human malaria.

Although not a endemic disease in Britain today it has been in the past, even as far north as Yorkshire.

In medieval times it was known as the ague and was a relatively common killer in wet and marshy areas, like the Vale of Pickering, where mosquitoes proliferated. The last cases of home-grown malaria in the UK were as recent as the 1800s.

The bug that causes human malaria, Plasmodium vivax, is very particular about its insect host and can only live in the bodies of mosquitoes of the genus Anopheles, five of which live in our country.

The disease is only currently a problem of tropical countries because P vivax needs high temperatures to multiply in the mosquito’s body but global climate change could change all that.

Every year some holiday makers return home having contracted malaria abroad. If they are then bitten by a local Anopheles mosquito and our increasingly higher summer temperatures allow the P vivax to develop then the disease could be passed on. The World Health Organisation is of the opinion that endemic malaria will return to Britain within the next 50 years - a scary thought.