Several days ago, in the still water of a ditch just south of Barcelona, a modern-day dragon emerged from her cocoon, her spindly legs balancing her metamorphosed shape precariously on the water’s surface. It seems harsh, in the love-laced breezes of springtime, to say that this dragon was female, but such is the biology of modern-day dragons, and I am a scientist bound to recount the data as it comes. Once stabilized on the water, the dragon fluttered her newly-formed wings and flew low across the warming fields to search for the blood of her prey.
Last April 23 Barcelona’s streets were filled with roses and books in celebration of its patron saint, San Jordi (Saint George). Legend has it that on the 23rd of April, San Jordi slayed a dragon just south of Barcelona before it could devour a beautiful princess. From the blood of the dragon sprouted a rose, which the knight presented to the princess. Hence Barcelona’s celebration of the day of San Jordi. In 1923 the celebration protagonists noted that both William Shakespeare and Miguel Cervantes, creator of the would-be knight, Don Quixote, had died on April 23 in 1616. Thenceforth books are exchanged with roses.
Carles Aranda is a dragon slayer. Every morning he commutes from the center of Barcelona to his office in a renovated farmhouse, or “masia”, by the banks of the LLobregat River just south of Barcelona. From his desk overlooking the fields towards the airport, he strategizes battles against mosquitoes that attack the princesses, princes, children, and sages, all citizens of the LLobregat Delta, the suburbs of Barcelona, and the neighboring villages and towns of Catalunya. He has exchanged the sword of San Jordi for the Ultra-Low Volume (ULV) sprayer, a truck-mounted industrial fogger, and barrels of ecologically inoffensive bacteria called Bacillus thuringiensis (BTI) which parasitize and kill mosquito larvae in the still water of ditches and ponds. He carries the banner of public health against the modern-day dragons that not only plague us with their itchy bites but also risk felling us with pathogens incubating in their salivary glands. Viruses that cause hemorrhagic yellow fever, West Nile virus encephalitis, dengue, and chikungunya, collectively known as arboviruses (for ARthropod BOrne VIruses), are all transmitted to humans through the bites of female mosquitoes (male mosquitoes feed mostly on sugar and do not generally seek human blood).
Last April 23, on the Day of San Jordi, Carles was teaching students in a one-week course on arboviral diseases conducted by ISGlobal and the University of Barcelona. The students came from countries around the globe: Peru, Colombia, Germany, Spain, Australia and Uganda. Their backgrounds included expertise in medicine, veterinary science, entomology, and laboratory science. They came to ISGlobal to learn the fundamentals of arbovirus biology and transmission dynamics as well as the strategies for diagnosis, management and prevention of arboviral diseases. Their professors included Carles and other internationally recognized arboviral disease experts: Lyle Petersen, the Director of the Division of Vector-Borne Infectious Diseases at the United States Centers for Disease Control and Prevention; Paul Reiter, a leader of entomologic research on dengue, yellow fever, West Nile virus, and malaria at the Institut Pasteur in Paris; Mikel Martinez, head of laboratory diagnostics for arboviral diseases at the University of Barcelona’s Hospital Clinic; Matthias Niedrig, a virologist at the Robert Koch Insitute in Berlin; Herve Zeller from the European Centers for Disease Control in Stockholm; and Jean Lang who has led dengue vaccine field research at Sanofi-Pasteur pharmaceutical company in Lyon. With Lyle, I co-directed the course, bringing my own enthusiasm for understanding the biology of these diseases and for applying the rapidly accumulating knowledge towards public health interventions. Because of the complex and shifting interplay between human ecology, vector biology, and viral pathogenesis, the enthusiasm for learning is, frankly, easier to muster than the application of the knowledge gained.
The students learned how previous dragon slayers like General William Gorgas in 1905, and Fred Soper in the 1950s led campaigns that nearly vanquished the mosquito vector of yellow fever and dengue from the Americas. Region by region, country by country, these men systematically eliminated the mosquito breeding sites, battling the mosquito to near extinction in the treated areas. But the world’s population has grown from less than 2 billion in those years to over 7 billion today, largely through growth in cities, and the quest to extinguish the dragon has become almost Quixotic. The dramatic increase in urban populations, the rapid travel between distant cities, and the tremendous expansion of international commerce has made mosquito control much more complicated. The dragon returned, so that today epidemics of dengue sweep through cities of Latin America, Asia and Africa causing millions of cases of feverish disease. West Nile virus, previously mostly silent in the Old World, invaded America 15 years ago and has spread across the North American continent killing hundreds of people. Chikungunya virus was recently imported into Europe during massive outbreaks in India and the islands of the Indian Ocean, resulting in an epidemic of chikungunya fever in Italy and local transmission in France. Yellow fever continues to cause thousands of preventable deaths in tropical areas of Africa and South America, and Japanese encephalitis cripples children in Asia.
The course introduced students to new swords and shields that could defend us against these diseases. Entomologists are developing methods to infect mosquitoes with bacterial parasites that can reduce their lifespan and decrease their ability to transmit pathogenic viruses. New vaccines are on the horizon. Developments in laboratory techniques have forged new diagnostic tests for the early detection of arboviral infections. New public health surveillance systems based on the internet are tracking the dragon’s movement, detecting when it sleeps and determining when and where it might awake.
Sant Jordi slayed the dragon in a field just south of Barcelona. As students gathered around the masia on the banks of the LLobregat last April 23, Carles hung a carbon-dioxide baited mosquito trap from the branch of a fig tree. Two days later he would bring into class the captured mosquito that had emerged from the nearby ditch. On the sun-dappled grass beside the old stone walls of the masia someone found the body of a small lizard, wizened and desicated by the sun. Carles picked it up. It looked…just like… a long-dead dragon.