New pathways for pathogens

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Updated: November 21, 2014 8:40:42 AM

Thanks to urbanisation, viruses are jumping species barriers

Pathogens are known to jump species—HIV is the most celebrated example—but suddenly, they are vaulting the biology barrier with the alacrity of performing fleas. The latest organism with its name up in lights is the Chlorovirus ATCV-1, a large virus which was believed to restrict its unwelcome attentions to the green freshwater algae seen in lakes and streams. But now, researchers at Johns Hopkins University and the University of Nebraska in the US have detected it in the throats of 44% of 92 humans surveyed.

That very 44% of humanity shows, in the words of the researchers, “modest but statistically significant decrease in the performance on cognitive assessments of visual processing and visual motor speed.” In politically incorrect terms, that means that almost half of us are a bit slow on the uptake, only because of a minor throat infection. The discovery opens up a new line of inquiry in the life sciences—apart from altering lifestyles (by keeping people in bed, for instance), can infections also alter human behaviour? In turn, that could open up a rich minefield of alibis for the bizarre excesses of humanity: “Your Honour, a bug made me do it.”

Meanwhile, Dalbir Singh of the University of Sarawak reports that the most severe cases of malaria in Malaysian Borneo are caused not by the species of the malarial parasite which infects humans, but that which infects monkeys—Plasmodium knowlesi. It is not transmitted human-to-human; the default route appears to be mosquitoes biting monkeys and then humans. This species-hopping behaviour was first confirmed in 2004 and has intensified. The vectors appear to be daytime-biting mosquitoes, which may interest malaria control officials in India, where day-biters transmit dengue.

Such instances of viruses jumping species must fascinate specialists working on the latest and biggest Ebola outbreak in West Africa, but Nature reports that they missed the opportunity presented at a meeting of the American Society of Tropical Medicine and Hygiene at New Orleans, which Singh addressed. Most of them kept away, since Louisiana is busily quarantining every human coming in from the hot zone, irrespective of their symptoms. Just another instance of America’s astoundingly parochial reaction to a global threat, which had sparked a hubbub of consternation followed by cries of outrage.

How do you contain a haemorrhagic fever in a globalised world where millions of people cross borders every day? Why, by locking down the destination airports, of course. What could be more natural than to turn your nation into a silo and let the rest lump it? In a remarkable departure from its history of anchoring and leading multilateral humanitarian action, the US government has extended itself less in the battle against the latest Ebola outbreak than NGOs like Médecins Sans Frontières. A fast-moving pandemic is best contained by isolating the affected in the hot zone and investing in their cure, to reduce the population capable of transmitting the disease as rapidly as possible. At the same time, practices facilitating the transmission of Ebola from animals to humans should have been discouraged. Instead, the US has spent its energies domestically, isolating the unaffected in its territory from a potentially infected world. Such neglect can only increase the probability of a pandemic, from which no nation can remain fully fire-walled.

Is species-jumping more common than before? If the trend is accelerating, preventive and social medicine will be grappling with its impact within decades, if not years. Ebola and HIV are perceived to have jumped from simians to humans by two related processes. The Simian Immunodeficiency Virus may have infected humans and mutated into the HIV when the two species came into close contact with each other. HIV is generally dated to the colonial period when rapid urbanisation, changed cropping patterns and wider exploitation of resources altered habits and habitats for both human and animal. Ebola is specifically traced to ‘bushmeat’—game meats which include simian flesh, which is prized by various cultures the world over, including in Africa. If hunters are cut or scratched while butchering their prey, they can be infected by their bodily fluids.

The theory of transmission by fluids is popular for its simplicity, but habitat change bringing species into unprecedented proximity could be a sufficient condition. Urbanisation forcing animals to share space with humans—and be bitten by the same bugs—could account for humans falling prey to monkey malaria, for instance. The global population explosion will bring more and more species into persistent contact with humans, and alter human food practices too. For the present, the life sciences may want to look more closely at (if only to rule out) the role of species-hopping organisms in humanity’s myriad disorders, from seasonal sniffles to conditions of unknown aetiology—which in themselves range from mysterious medieval fevers to the very modern irritable bowel syndrome. If an algal virus is making humans stupid, anything is possible.

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