Picture this: two men with heavy backpacks, clambering up a
mountainside in the middle of August in the Inca area of Majorca, 35km
north-east of Palma. Neither tourists, nor hunters, they are actually
scientists heading for Ratapinyades cave to catch bats. The aim is to
study the viruses they carry.
Bats are suspected of being behind
Mers-CoV, a new coronavirus that is causing alarm in the Middle East. Also implicated in a related virus, which caused the
Severe Acute Respiratory Syndrome (Sars) in 2002-03 in China, bats seem to be important reservoir hosts for many emerging or re-emerging viruses.
The
viruses have caused serious infections ranging from Ebola fever to
measles, through encephalitis and rabies. So gaining a better
understanding of the viral profile of bats is clearly important.
Unlike other
animals,
chiropterans do not die when they catch the viruses, which they can
transmit through their saliva or excrement. Jordi Serra Cobo and Marc
Lopez Roig, two biologists at Barcelona University, have been studying
them since the 1990s, when few scientists paid much attention to bats.
They have explored colonies in Catalonia and on the Balearic Islands in
an effort to understand the infection dynamic, focusing on rabies, which
belongs to the lyssavirus group.
It is often exhausting work.
Near Inca, after crossing an almond orchard where sheep were grazing and
reaching the end of a track used by hunters, they climbed Puig Santa
Magdalena. The temperature was over 30C.
After struggling up a
rocky path they finally reached the cave. The entrance had been closed
with an iron gate since studies by Catalan researchers and a team led by
Hervé Bourhy, from the Institut Pasteur in Paris, demonstrated the
frequency with which the bats occupying the cave – numbering about 1,000
at any time – acted as carriers for the rabies virus.
To capture
these flying mammals the scientists spread nets and waited patiently in
the gloom. With the sheep bleating outside, it was not always easy to
hear the squeak of bats trapped on their way out in search of food.
Two
days later, at Sa Guitarreta, near Llucmajor, some 30km south-east of
Palma, Cobo and Roig carried out another procedure, this time in
daylight. Following a dry stone wall, bordering another almond
plantation, they climbed down a rockface and entered another cavity.
About 25 metres below ground, a tunnel opened onto a great hall, a good
15 metres high.
At first, the only sounds to be heard were the
beating of wings. Then, in headlamps, they discovered dozens of bats
hanging upside down, while others, perhaps disturbed by the intruders,
flew back and forth.
Roig unpacked a great butterfly net on the
end of a telescopic pole, rising eight metres into the air. Moving
cautiously, because the ground was slippery, he climbed on to a rock in
order to reach the ceiling. Once netted – and taking care to avoid any
bites – the scientists sorted the animals by species and placed them in
canvas bags. The largest had a wingspan of 40cm.
On both
occasions, it took no time to catch several dozen samples. The
researchers then worked for more than two hours in a sort of a field
laboratory, set up on an old car bonnet or a flat rock.
Each
specimen was treated in exactly the same way. They were examined to
confirm their species and gender, then checked for a possible
identification ring. In some cases, a numbered ring was fitted. Since
1995 Cobo's team has ringed 2,600 bat specimens on the Balearics and
more than 6,000 in mainland Spain.
The scientists then took a
saliva sample using a swab. The bat was laid on its back and its left
wing was spread out to allow a blood sample to be taken. At Sa
Guitarreta, Cobo also took excrement samples.
The blood samples
are centrifuged and deep-frozen, prior to being analysed to isolate
specific virus antibodies (lyssavirus or flavivirus, the latter genus
comprising the dengue, yellow fever, Japanese encephalitis and West Nile
viruses). Ribonucleic acid (RNA), the genetic material of these
infectious agents, will be isolated too.
The saliva can also be
used to detect lyssaviruses. The excrement may contain signs of
coronaviruses and hantaviruses responsible for pneumonia or hemorrhagic
fever. The results will take a few weeks.
In its most recent
publication, in the May issue of PLoS ONE, the team led by Cobo and
Bourhy revealed the ecological factors associated with the prevalence of
European bat lyssavirus-1 in the serum of almost 2,400 bats captured in
2001-10 in Spain and the Balearics. The lyssavirus was found in more
than 20% of the serum samples, rising to 40% for one particular species.
Virus
prevalence peaks in July, in the middle of the breeding season. Above
all, the high density of a colony (more than 500 specimens) and the fact
that several species lived side-by-side was linked to a high prevalence
of lyssavirus.
The bats represent the first link in the chain
that transmits the virus to humans, leading to public-health measures
such as closing bat caves to restrict the risk of human contact.
However,
Cobo and Roig say there would be no point in wiping out bat colonies.
"They don't attack humans and act as sentinels for viruses circulating
in a particular area. Protecting biodiversity also protects human
health," Cobo said. Roig points out that "bats, which must eat between a
quarter and half of their body weight daily, have a devastating effect
on insect populations, which are also vectors for disease".
To
confirm this point the two scientists recall that in 2003 floods on
neighbouring Minorca killed many bats, drowned in certain caves. In the
aftermath, two parasites thrived, attacking oak and pine trees.
This article appeared in Guardian Weekly, which incorporates material from Le Monde
Dawn Hepp shows off the wounds on her neck. (Courtesy Dawn 
