Global Wildlife AIDS
Associated With
Neonicotinoid Insecticides

Immunity Deficiency In Bats

This feature is a continuation of an article by Dr Rosemary Mason and Palle Uhd Jepsen. Go to previous pages of immunity deficiency article

Bats in the US

Coincidentally, it was 2006 when White Nose Syndrome (WNS), a virulent and fatal fungus disease of hibernating bats, came to the attention of ecologists [31].

It was first found in a cave in New York State in the 2005/6 winter and rapidly spread through the north-eastern states.

A powdery white nose tip was pathognomonic of the disease and when the powder was cultured a fungus, Geomyces destructans was grown. This infected the skin and wing membranes of bats and was associated with unprecedented numbers of deaths. It affected six different species of bat.

The mortality in a colony could be up to 95% and it was reported that 1 million bats had died since 2006. Alan Hicks of the New York State Department of Environmental Conservation said that it was “the gravest threat to bats… ever seen.”

Bats with WNS use up their fat stores too quickly and cannot produce the energy they require. They exhibit unusual winter time behaviour, such as flying out of caves in the daytime when there are few insects available; they become disorientated, dehydrated and eventually starve to death.

In August 2010 Frick et al., using a combination of existing field data on hibernacula counts, rate of spread of the disease and mathematical models, predicted that regional extinction of the little brown bat in the north-eastern US was likely to occur [32].

A map showed the rapid extension of WNS, year by year, starting in New York State and spreading throughout the north-eastern and Mid-Atlantic regions and into Ontario and Quebec in Canada. The abstract stated that: “Novel diseases can have serious impacts on naïve wildlife populations, which in turn can have substantial impacts on ecosystem integrity.”

The nocturnal ecosystem services provided by bats are invaluable and include insect control, pollination and seed dispersal.

In December 2010, a cull was considered, but rejected. By February 2011, Foley et al. in Conservation Biology reported that the eastern disease was beginning to spread westwards and they eventually expected it to cross the Rocky Mountains and enter California [33].

Various strategies of disease management and control were considered but most were impracticable. The apparent virulence of the pathogen and the high mortality suggested that the existence of recovered and immune individuals was unlikely.

Bats in mainland Europe

In March 2009 (published Feb 2010), Puechmaille et al. found the fungus on a single bat in a cave in France, but without other evidence of disease [34].

They raised the possibility that the fungus was not the primary cause of death “but acts as an opportunistic pathogen in bats already immune-compromised by other pathogens such as viruses or bacteria.”

In a German-led multicentre study published in Emerging Infectious Diseases in August 2010, hibernating bats with obvious fungal growth were sampled in Germany, Switzerland and Hungary [35].

Despite laboratory confirmation that these bats were colonised by Geomyces destructans, at that time deaths were not observed. The researchers said “bats in Europe appear to coexist with G. destructans.” They thought that the European bats might have been exposed to the fungus for a longer time and therefore had developed immunity to it.

They also stated:  

“Although we have searched the literature describing observations in hibernating bats, we have been unable to find any similar historical accounts of white fungus growing on live hibernating bats before the recent emergence of WNS.”

In May 2010, Professor Paul Racey, Founding Chairman of the UK Bat Conservation Trust and Visiting Professor at the University of Exeter Centre for Ecology & Conservation, said that although the fungus “has been found in Europe at this point we don’t have a mass mortality, we just have the fungus” [36].

However, by November 2010, a report from the Czech Republic and Slovakia said that the numbers of hibernation cave sites in which the fungus was found were increasing rapidly, from 33 at the beginning of winter to 76 at the end, and they said that sickness was starting to occur in some of the bats [37].

In fact, from 2008 bat populations had started to decline, so perhaps the disease was already affecting them at that time.


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