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Published Date: 2019-07-22 12:52:01
Subject: PRO/AH/EDR> Malaria, avian - UK: (London) sparrow
Archive Number: 20190722.6581354
MALARIA, AVIAN - UK: (LONDON) SPARROW
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Date: Thu 17 Jul 2019 00:04 BST
Source: Mail Online [edited]
https://www.dailymail.co.uk/sciencetech/article-7253399/Avian-MALARIA-decline-humble-European-house-sparrow-suburban-areas.html


Noisy and cheeky, they used to be a regular sight in people's gardens as one of Britain's most common birds. But the number of house sparrows has more than halved since the [1970s], and a new study suggests 'avian malaria' may be to blame.

Avian malaria, spread by mosquito, can make sparrows lethargic and unable to eat, killing many through starvation.

Researchers who tracked sparrows in 11 suburbs of London have now discovered almost 3/4 carry the infectious disease.

As warming temperatures and wetter weather may help avian malaria to thrive, there are concerns it could wreak havoc in the sparrow population, similarly to the trichomonosis parasite in British greenfinches.

The study, led by the Zoological Society of London, concludes that the disease particularly affects juvenile birds, which are vital for breeding to maintain sparrow numbers.

Dr Daria Dadam, who led the study and now works for the British Trust for Ornithology, said: 'Parasite infections are known to cause wildlife declines elsewhere and our study indicates that this may be happening with the house sparrow in London. We tested for a number of parasites, but only _Plasmodium relictum_, the parasite that causes avian malaria, was associated with reducing bird numbers.'

Sparrows are among Britain's best known birds, hard to miss in their noisy, constantly chirping groups. They show little fear of people, whose gardens they raid for scraps of food.

But their population has fallen by 70 per cent between 1977 and 2016, with declines in both urban and rural areas. In London's suburbs, which were the focus of the new research, house sparrow numbers are down 71 per cent from 1995.

Researchers took blood and faecal samples from sparrows in areas ranging from Enfield in north London to Sutton in the south and Fulham in the west, as they searched for parasites over 3 years.

In some areas, 100 per cent of birds were infected with the avian malaria parasite, and when the birds were counted, many juvenile sparrows did not survive the winter.

The findings, published in the journal Royal Society Open Science, suggest the downturn in the suburbs may be linked to avian malaria.

This follows studies ruling out domestic cats as a cause of falling sparrow numbers, and casting doubt on whether sparrowhawks are responsible.

Some experts suggest that, because sparrows fail to move very far, populations may be becoming inbred, which would make their immune systems less able to fight off avian malaria.

It may also be the case that the infection is becoming more intense, as mosquitoes thrive in warmer, wetter British weather.

The rates of malaria seen in the suburban sparrows is higher than has been recorded in any other northern European wild bird species. In 7 out of 11 sites, the birds were in decline, and these populations were more strongly infected by the malaria parasite.

It can kill them by causing brain and liver damage, or by making the sickly birds more vulnerable to cold winters and predators.

Dr Will Peach, head of research delivery at the RSPB said: 'House sparrow populations have declined in many towns and cities across Europe since the 1980s. This new research suggests that avian malaria may be implicated in the loss of house sparrows across London.

'Exactly how the infection may be affecting the birds is unknown. Maybe warmer temperatures are increasing mosquito numbers, or the parasite has become more virulent.'

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Communicated by:
ProMED-mail from HealthMap Alerts
<promed@promedmail.org>

[Avian malaria is a disease caused by protozoans in the genus _Plasmodium_, which are transmitted by mosquitos. It is known that, within limits, arthropod populations are favored by heat and moisture. Therefore, it is expected that climate change will influence vector-borne diseases. In fact, a number of vector-borne human and domestic animal diseases, including malaria, African trypanosomiasis, tick-borne encephalitis, yellow fever, plague, dengue, African horse sickness, and bluetongue, have increased in incidence or geographic range in recent decades.

UK anophelines are considered competent vectors. Climate modelling has suggested that transmission of _P. vivax_ (and to a lesser degree _P. falciparum_) could already occur in the UK, although no cases have been reported.

It should be taken into account that malaria might not be the only culprit of sparrow population declines. In recent years, a number of wildlife population crashes have been linked to impoverished health linked to a multifactorial web of causation. When parasites/pathogens that are part of the normal parasite community of a host are unusually pathogenic, there might be some underlying context that is affecting that host-parasite relationship. Anthropogenic stressors (including climate change) may disrupt that relationship. When the stress-host-parasite equilibrium is broken, the tolerance and resistance to parasites is reduced and hosts become increasingly deteriorated. Both exposure to transmissible diseases and host susceptibility to infection increase, resulting in a vicious circle (for a review on the subject see https://doi.org/10.14409/favecv.v14i1/2.5160).

The reference for the scientific article referred to above is
Dadam D, Robinson RA, Clements A, et al. Avian malaria-mediated population decline of a widespread iconic bird species. Royal Society Open Science 6(7); https://royalsocietypublishing.org/doi/10.1098/rsos.182197
- Mod.PMB

HealthMap/ProMED-mail map of England, United Kingdom: http://healthmap.org/promed/p/283]

See Also

2018
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Malaria, avian - UK: (England) penguin, zoo colony 20181213.6207806
2016
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Malaria, penguin - UK: (England) fatal, zoo colony 20160922.4507887
Malaria, avian - USA (02): (ME) loon 20160412.4155265
Malaria, avian - USA: (ME) loon, 1st report 20160411.4152932
2012
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Malaria, avian - USA: (AK) climate change 20120928.1314598
2011
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Malaria, avian - UK 20110818.2511
2003
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Malaria, avian, crowned cranes - South Africa 20030207.0327
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