Having spent two months travelling in the primary rainforests of Borneo, I thought that a four-month journey in the country between the Orinoco River in Venezuela and the Amazon in Brazil would pose no particular problem.

I reread my nineteenth-century heroes: the seven volumes of Alexander von Humboldt’s Personal narrative of travels to the equinoctial regions of the New Continent during the years 1799–1804 (1814–29); William H. Edwards’s A Voyage up the River Amazon (1847); Alfred Russel Wallace’s A Narrative of Travels on the Amazon and Rio Negro (1853); Henry Walter Bates’s The Naturalist on the River Amazons (1863) and Richard Spruce’s Notes of a Botanist on the Amazon and Andes (1908).

There are no leeches that go for you in the Amazon jungles, an absence which would represent, I felt, a great improvement on life in Borneo. But then there are many of the same amoebic and bacillary dysenteries, yellow and black water and dengue fevers, malaria, cholera, typhoid, rabies, hepatitis and tuberculosis – plus one or two very special extras.