In the southwestern highlands of Ethiopia, the city of Jimma is located on the old caravan route. Known for its markets, this city with a population of 88,000 people grew rapidly in the 90s. (As of 2007, it had 121,000 inhabitants.) However, along with the growth of prosperity by the standards of Ethiopia, the city remained poor by the standards of Western Europe. Many citizens lived in houses with clay walls and roofs made of corrugated metal. Latrines were often placed outside the dwelling. Only a few houses had electricity. There was almost no tap water anywhere. People took drinking water from common wells.
In general, the city of Jimma was experiencing a period of epidemiological transition, approximately comparable to the same transition in some areas of the United States at the turn of the XIX–XX centuries. Nevertheless, the prevalence of allergic diseases has already increased. A decade earlier, almost no one in Jimma had heard anything about asthma, but now every twentieth patient who went to the hospital had asthma symptoms. This apparent increase in the prevalence of asthma attracted the attention of John Britton and his colleagues from the University of Nottingham.
There were many theories about the causes of asthma: environmental pollution, smoking, dust mites, nutrition, and much more. However, the sudden appearance of this disease in Jimma recently indicated that, whatever the causes of asthma, they begin to manifest themselves at the very beginning of the urbanization process. For the researcher, the temporary proximity of what was happening was a real find. In Europe, the asthma epidemic had its roots in the past for decades, maybe even a century. However, Britton hoped that in Jimma, where the spread of this disease has just begun, the reasons remain more obvious. He hoped that he would be able to establish the factors of the spread of asthma before the ” trail cools down.”
The first stage was to assess the prevalence of asthma in Jimma compared to the surrounding countryside. Since Richard Godfrey’s work in the Gambia two decades ago, other researchers have also noted that in Africa, asthma is more common in urban environments and among the wealthiest segments of the population. In the area of Jimma, the same pattern took place. Britton and his colleagues found that the prevalence of asthma in the city itself is three times higher than in the rural areas located around it.
While the living conditions in the city resembled Great Britain at the end of the XIX century, the countryside was more like the early Neolithic. The inhabitants of rural Ethiopia lived in round huts with clay walls, thatched roofs and earthen floors. Latrines were rare. Most Ethiopians relieved themselves in the bushes or in the fields. “They live there the way people lived a thousand years ago,” says Britton.
At the next stage, it was necessary to compare the data obtained. The researchers, to their surprise, were immediately able to discard such a factor as air pollution. There were no large industrial enterprises at all in Jimma and there were few motor vehicles. In the city and in the countryside, the air quality was about the same. In addition, it was possible to ignore the differences in nutrition. The inhabitants of Jimma ate food made from animal meat and cereals grown in nearby villages. The city has not yet switched to the products of agro-industrial farms and pre-processed packaged food products. All residents of Jimma and the surrounding area ate traditional Ethiopian cuisine. Two decades earlier, Australian scientists working in the habitats of the Fore tribe in Papua New Guinea explained the recent increase in the prevalence of asthma in this region: this disease appeared there immediately after the beginning of constant contacts with residents of Western countries, in connection with the use of Western-style bedding. These researchers believed that, in addition to creating ideal conditions for sleeping, synthetic bedspreads provide a rapid development of dust mites, and this, in turn, leads to the development of asthma.
Britton did find that people who live in better homes and use synthetic bedding are more at risk of asthmatic wheezing. Dust mites played a role in this. In the city, sensitization to dust mites increased the risk of asthma tenfold, which strongly supported the popular view: we were right to blame these tiny arachnid arthropods for the asthma epidemic.
But maybe this is not quite true. Observations carried out in rural areas removed the responsibility for the spread of asthma from dust mites . There were much more of them in rural huts, although asthma was less common there. Among rural residents, sensitization to dust mites was noted more often; this could be established by monitoring the reaction to skin piercing and the introduction of dust mite protein into a small wound. Nevertheless, such sensitization was not a predictor of allergic diseases, as it would be in London. In the rural environment, there was no connection between these two phenomena. For Britton, this meant one of three options: either something is good for a person in a rural area, or something is bad for him in an urban environment, or both.
Britton and his colleagues compiled a list of variables and began analyzing them. They excluded such a factor as exposure to measles, which was the same in both groups. Smoking, which is more common in rural areas, could not explain the existing differences. The same could be said about infection with hepatitis A, which, according to available observations, in some cases even reduced the risk of asthma. Exposure to insecticides, which was generally believed to increase the risk of asthma, also had no effect on it. Only one variable showed a constant inverse relationship with asthma: hookworm infection. The presence of the helminth Necator americanus halved the probability of bronchial obstruction in both urban and rural areas . Infection with parasites also explained why sensitization to dust mites does not cause bronchial obstruction in rural areas. By suppressing the host’s immune response, helminths contributed to the development of tolerance to foreign proteins. Krivogolovki along the way taught a person to be tolerant of dust mites.
What does all this mean? First, after the disappearance of helminths in Ethiopia, we could expect an increase in the prevalence of allergies to dust mites and, most likely, asthma. This is the conclusion reached by Pritchard, who closely followed this work and was a co-author of one of the studies. “We were fed up with all these stories and decided to check them out,” he told me.
In 2000, Pritchard collected a batch of hookworms on the island of Karkar and hid them in his luggage. His colleague Alan Brown infected himself with a spare batch. Who knows how the customs service will react? Then the scientists boarded a plane flying to the UK. A few months later, Brown, who later determined that his hookworm colony numbered three hundred individuals, noted with satisfaction that the hay fever that he had suffered from all his life was almost gone.