It's easy to see the appeal of an adventurous summer trip: a jealousy-inducing suntan, memorable photos with the local wildlife and anecdotes aplenty - but with them, too, comes the risk of a brush with species that may well cast a long shadow after your return. Yet it is not the exotic creatures that are the most perilous, but the ones that seem near-harmless, from dogs to monkeys and pigs, that are capable of causing the most damage. It is these animals that have killed many more people than lions or tigers, after all - hosting the Aids virus initially, in the case of chimps, while bats triggered the Ebola crisis of 2014.
But just how likely are you to pick something up from an animal abroad? Diseases that can jump from animal to human are known as zoonoses: some 60 per cent of all human diseases are zoonotic in origin and, according to the US Centers for Disease Control and Prevention, they cause 2.5 billion cases of human illness and 2.7 million human deaths worldwide each year.
Take care when coming into contact with the following on your travels.
Though it's tempting to pet that stray loitering outside your villa, the risk of rabies persists, and kills 59,000 people worldwide each year. Worse, perhaps, is the news that according to new research, your beloved pet could be the source of the next flu pandemic, with experts from New York's ICAHN School of Medicine recently discovering that domestic dogs harbour flu viruses that may one day jump to humans.
A cave tour features on many a tourist itinerary, but the menace that bats are capable of inflicting isn't reserved for horror films. The EcoHealth Alliance, a US-based organisation that aims to identify every virus that could jump from animals to humans, has come up with a list of the planet's most dangerous animals, assessed on how likely they are to harbour undiscovered pathogens that could infect us. Bats are chief among them, making up all of the top 10. More than 200 viruses have been associated with them, explains Dr Peter Daszak, the organisation's president, who calculates that there are potentially 17 unknown viruses waiting to be found in each of the estimated 1,000 bat species.
Ebola, which has killed 13,000 people since it was first discovered in 1976, originated in bats, and scientists believe they probably produced the virus that evolved into severe acute respiratory syndrome (SARS), which swept the globe in 2003. Fruit bats are also thought to be the reservoir for the deadly Nipah virus, which in May this year killed 16 people in Kerala, India.
Keep an eye out for the Aedes albopictus mosquito, spotted moving northwards to France, Italy and Croatia, and responsible for both dengue and Zika - and keep slapping on the insect repellent. Although a disease carrier rather than a disease reservoir, the mosquito was responsible for 216 million cases of malaria in 2016, including 445,000 deaths - the majority of which occur in sub-Saharan Africa, as well as south-east Asia, the Americas and the Pacific.
Monkeys and apes
Monkeys, apes, gorillas and chimps are regular features on holidays from Gibraltar to Gambia, but they are thought to play host to at least 75 unique viruses that could transcend the species barrier. Our furry cousins are the likely source of yellow fever, a sometimes fatal virus transmitted through mosquito bites, while chimps were the original source of HIV/Aids, one of the most deadly diseases to have crossed the species divide, having infected 70 million people and killed at least 35 million since the start of the pandemic in the Eighties.
The "unprecedented level" of bushmeat we consume - with monkeys and apes a popular delicacy in places such as Angola and Ghana - is also increasing the risk of another disease bridging the species divide, says Dr Daszak, adding that "a lot of these viruses are spilling over because we catch animals and eat them".
In their various guises from household nuisance to lovable pet, mice, rats, gerbils, hamsters, guinea pigs and other rodents carry at least 80 known viruses that are transferable to humans. From the New York subway to city streets just about anywhere, our constant close contact with them (and their sizeable population) make them a particular risk. "They are the most diverse order of mammals on the planet, with perhaps some 2,300 to 2,500 species," says Dr Kevin Olival, vice-president of the EcoHealth Alliance.
Last week, rats were implicated in the spread - and death of one victim - of Lassa fever, a particularly nasty haemorrhagic disease endemic to Nigeria, which in severe cases causes facial swelling, fluid retention in the lungs, and bleeding from the mouth, nose, vagina and gastrointestinal tract.
Rats also carried the fleas responsible for the plague that killed 50 million people in Europe in less than a decade during the Middle Ages; now, the disease continues to strike places such as Madagascar, where a major outbreak last year saw 2,300 people infected, and more than 200 deaths.
"There's good reason for [flu] to be one of the most worrying zoonotic diseases," says Dr James Rudge, a zoonotic specialist at the Bangkok branch of the London School of Hygiene and Tropical Medicine. Birds are host to dozens of types of avian flu, including the strain responsible for the 1918 flu pandemic that killed 50 to 100 million people; they were also the reservoir of the deadly H5N1 strain, which has killed 400 people since 1997, as well as newly emerging fatal strains such as the H7N9 Chinese bird flu, which England's deputy chief medical officer recently singled out as having the potential to spark a worldwide flu pandemic.
Just like the flu viruses found in birds, influenza viruses in pigs are also prone to mutating into new strains. That's what happened in 2009 when pigs became the source of a deadly new form of flu that had mutated and recombined from existing avian and human forms of the disease.
The 2009 H1N1 swine flu outbreak killed 284,000 people across six continents in one of the worst flu pandemics of recent years.
In addition to flu, pigs spread a variety of other nasty bugs including streptococcus suis - a bacteria that causes septicaemia and bacterial meningitis in humans. Pigs are also the conduit for a number of other zoonoses including the Nipah virus, which swine pick up from bats and then pass directly to humans. In Malaysia in 1998, where the virus was first identified, there was a mass culling of pigs after they were found to have passed on the virus to about 300 people, 100 of whom died.
Tourism is returning to rude health in Middle Eastern countries such as Egypt, but it is there that camels - an important source of milk and protein, as well as their beach?riding potential for visitors - may cause several zoonotic diseases such as Middle East Respiratory Syndrome Coronavirus (MERS-CoV), which has killed almost 800 people since 2012.
Recently, a brain disease similar to "mad cow disease" in cattle has also been discovered: though "mad camel disease" has yet to infect any humans, researchers have not ruled out the possibility.
The Telegraph, London