At the same time, the health world was facing a much deeper ignorance. Zika was generating a huge volume of questions, few of which could yet be answered. ‘Rarely have scientists engaged with a new research agenda with such a sense of urgency and from such a small knowledge base,’ wrote epidemiologist Laura Rodrigues in early 2016.[9] For me, the first challenge was to understand the dynamics of these Zika outbreaks. How easily did the infection spread? Were the outbreaks similar to dengue ones? How many cases should we expect?
To answer these questions, our research group started to develop mathematical models of the outbreaks. Such approaches are now commonly used in public health, as well as appearing in several other fields of research. But where do these models originally come from? And how do they actually work? It’s a story that starts in 1883 with a young army surgeon, a water tank and an angry staff officer.
Ronald ross had wanted to be a writer, but his father pushed him into medical school. His studies at St Bartholomew’s in London struggled to compete with his poems, plays and music, and when Ross took his two qualifying exams in 1879, he passed only the surgery one. This meant he could not join the colonial Indian Medical Service, his father’s preferred career path.[10]
Unable to practice general medicine, Ross spent the next year sailing the Atlantic as a ship’s surgeon. Eventually he passed his remaining medical exam and scraped into the Indian Medical Service in 1881. After two years in Madras, Ross moved to Bangalore to take up a post as Garrison Surgeon in September 1883. From his comfortable colonial viewpoint, he claimed it was a ‘picture of pleasure’, a city of sun, gardens and pillared villas. The only problem, as he saw it, was the mosquitoes. His new bungalow seemed to attract far more than the other army rooms. He suspected it was something to do with the water barrel sitting outside his window, which was surrounded by the insects.
Ross’s solution was to tip over the tank, destroying the mosquitoes’ breeding ground. It seemed to work: without the stagnant water, the insects left him alone. Spurred on by his successful experiment, he asked his staff officer if they could remove the other water tanks too. And while they were at it, why not also get rid of the vases and tins that lay scattered around the mess? If the mosquitoes had nowhere to breed, they would have little option but to move on. The officer wasn’t interested. ‘He was very scornful and refused to allow men to deal with them,’ Ross later wrote, ‘for he said it would be upsetting to the order of nature, and as mosquitoes were created for some purpose it was our duty to bear with them.’
The experiment would turn out to be the first in a lifelong analysis of mosquitoes. The second study would come over a decade later, inspired by a conversation in London. In 1894, Ross had travelled back to England for a one-year sabbatical. The city had changed a lot since his last visit: Tower Bridge had been completed, Prime Minister William Gladstone had just resigned, and the country was about to get its first film parlour.[11] When Ross arrived, though, his mind was focused elsewhere. He wanted to catch up on the latest malaria research. In India, people regularly fell ill with the disease, which could lead to fever, vomiting, and sometimes death.
Malaria is one of the oldest diseases known to humanity. In fact, it may have been with us for our entire history as a species.[12] However, its name comes from Medieval Italy. Those who caught a fever would often blame ‘mala aria’: bad air.[13] The name stuck, as did the blame. Although the disease was eventually traced to a parasite called Plasmodium, when Ross arrived back in England the cause of its spread was still a mystery.
In London, Ross called on biologist Alfredo Kanthack at St Bartholomew’s, hoping to learn about developments he may have missed while in India. Kanthack said that if Ross wanted to know more about parasites like malaria, he should go and speak to a doctor called Patrick Manson. For several years, Manson had researched parasites in southeastern China. While there, he had discovered how people get infected with a particularly nasty family of microscopic worms called filariae. These parasites were small enough to get into a person’s bloodstream and infect their lymph nodes, causing fluid to accumulate within the body. In severe cases, a person’s limbs could swell to many times their natural size, a condition known as elephantiasis. As well as identifying how the filariae caused disease, Manson had shown that when mosquitoes fed on infected humans, they could also suck up the worms.[14]
Manson invited Ross into his lab, teaching him how to find parasites like malaria in infected patients. He also pointed Ross to recent academic papers he’d missed while out in India. ‘I visited him often and learnt all he had to tell me,’ Ross later recalled. One winter afternoon, they were walking down Oxford Street, when Manson made a comment that would transform Ross’s career. ‘Do you know,’ he said, ‘I have formed the theory that mosquitoes carry malaria just as they carry filariae.’
Other cultures had long speculated about a potential link between mosquitoes and malaria. British geographer Richard Burton noted that in Somalia, it was often said that mosquito bites brought on deadly fevers, though Burton himself dismissed the idea. ‘The superstition probably arises from the fact that mosquitoes and fevers become formidable about the same time,’ he wrote in 1856.[15] Some people had even developed treatments for malaria, despite not knowing what caused the disease. In the fourth century, Chinese scholar Ge Hong described how the qinghao plant could reduce fevers. Extracts of this plant now form the basis for modern malaria treatments.[16]
