14 years ago, just 20 kilometers from Madrid's Puerta del Sol, in Fuenlabrada, a massive and unexpected episode of contagion of a disease of animal origin, leishmaniasis, began to occur to humans. It was the largest outbreak in Europe of this infection caused by a parasite, which in its most serious form, the visceral form, is fatal in 90% of cases if it is not treated in time. The Epidemiology Service of the Community of Madrid detected for the first time the unusual increase in cases at the end of 2010, the first of the surprises that health officials were going to encounter. Nobody then expected that the outbreak would affect nearly 800 people for more than a decade. Even more shocking was discovering that the origin of a disease, usually associated with dogs, was the hares and rabbits that overpopulated Bosquesur, a huge forest park of more than 550 hectares. The Carlos III Health Institute has just published a detailed report entitled Comprehensive study of the community outbreak of Leishmaniasis in the Community of Madrid that analyzes what happened. Francisco Javier Moreno Nuncio (Seville, 59 years old), head of the Leishmaniasis and Chagas Disease Unit of the National Center for Microbiology, is one of its editors.
Ask. Was the outbreak really so exceptional?
Answer. Yes. It is something that there is no precedent for and that no one expected to happen. Leishmaniasis is endemic in Spain, but the outbreaks we had had were small. Nothing like this had ever happened in the Mediterranean basin.
P. What happened?
R. Several things coincided to form a perfect storm. The first was the environment. Bosquesur is a huge space that was left unbuilt between densely populated cities.
P. A forest park…
R. Yes. A paradise for hares and rabbits, with food available and without predators or activities such as hunting.
P. Wasn't this known to be a risk?
R. No. Some studies had shown that wild canids (wolves, foxes…) are a reservoir of the parasite. Someone else had also targeted small rodents. But the role of hares and rabbits was unknown. In Bosquesur there were many, but the percentage of infected people was also very high, 30% and 17% of the rabbits.
P. How does the parasite then reach people?
R. Through sandflies, a flying insect that, like mosquitoes, needs the blood of mammals to complete the reproductive cycle. If a sand fly bites an infected animal, it will undergo its own infectious process and, after about seven days, it will be able to transmit the parasite.
P. And in Bosquesur were there many sandflies?
R. Yes. They grow very well among leaf litter and places with organic matter, especially burrows. There were areas where more than 150 insects per square meter were collected.
P. But all these elements must be present in more places…
R. They may be, but not to that magnitude. Historically, in these areas south of Madrid some hunters suffered from cutaneous leishmaniasis, so we can conclude that the parasite was already there. There was a wild cycle with hares and rabbits, but it affected few people because the concentrations were low. Bosquesur gave rise to a perfect space for this wild cycle to grow until it reached densely populated areas where, in addition, practically no one had prior immunity.
P. When you think about these things, you imagine them in deforested and newly inhabited areas of the Brazilian jungle, not 20 kilometers from the center of Madrid…
R. This demonstrates the importance of properly managing peri-urban naturalized spaces.
P. Did infected sandflies enter homes?
R. Maybe they didn't enter, but they were all over the environment. If you went for a walk in the park, it was very possible that you would get stung. Also on the terraces of nearby bars and restaurants. And in patios and gardens.
P. Well, 800 infected seem few…
R. These are the cases diagnosed by the disease. There are thousands of asymptomatic people whose immune system coped with the infection without problems. An epidemiological survey revealed that up to one in five neighbors had been in contact with the parasite.
P. What is leishmaniasis?
R. It is a parasitic disease caused by a protozoan called Leishmania. It is a complex disease, with more than twenty protozoan species distributed throughout the world causing different types of clinical manifestations. The one that is endemic in Spain is called infant leishmania and that already gives us a clue as to what it is like.
P. Because?
R. Because it has that name because it affected children more. Healthy adults usually don't have too many problems. It affects more children and immunosuppressed people. And historically also to the most disadvantaged and poorly nourished groups.
P. And how does it manifest?
R. It produces two frames, basically. Visceral leishmaniasis is the most serious: the parasite reaches the internal organs, affects the liver, kidneys, bone marrow… It causes fever and anemia and, if not treated properly, leads to high mortality. The second is cutaneous and manifests itself only on the skin, so it receives less attention and often goes unnoticed. A hardening occurs in the area of the bite that sometimes evolves into an ulcer. It can be treated without even knowing the cause with systems such as the thermal scalpel.
P. Have there been deaths?
R. Not directly attributable to the outbreak. Although there have been serious cases and one death of a person with a transplant who was already in a very delicate state of health.
P. And what mistakes will have to be avoided in the future?
R. Do not rush to end the outbreak and do not relax prevention and control measures ahead of time. It happened to those responsible for the Community of Madrid that summer arrived, there stopped being new cases and they said: “The outbreak is over.” But the thing is that June is when people who will be diagnosed in December become infected, which is how long it takes for the parasite to cause serious symptoms. We must prevent this from happening again. We do not want to be alarmist, but we have had the worst outbreak in Europe next to Madrid and this can happen again anywhere.
P. Safe?
R. Yes, because climate change also works against us. The parasite is already endemic in the Iberian Peninsula and the Balearic Islands, and with higher temperatures, the months of sandfly activity increase.
P. The study says that the outbreak cannot be considered closed, but there is data that supports the idea that it is controlled. What does that mean?
A. That we cannot rule out that cases continue to occur or even increase again.
P. What does the data say?
R. Before the outbreak, we had about 20 or 25 cases of visceral leishmaniasis. Now there are about 50 or 60, although this is throughout the Community of Madrid. In part, these numbers may say that we are now better monitoring the disease and counting diagnoses better. But last year we had five cases in the Fuenlabrada hospital. There is a trickle that can still be attributed to the event. In a way we can say that the outbreak is more or less controlled, but that there will be greater transmission of the disease in the area.
P. Is it that complicated to end the problem?
R. It is a very complex disease. There are still rabbits and hares in the area. You can control their population, but you are not going to eliminate them. And there are also sandflies. Logically, it does not make sense to fumigate the entire park, although specific actions can be taken.
P. Neighbors have always complained about a lack of information and how the problem was handled.
R. Well, we have already said that it is complex. Furthermore, it is true that it also took time to become aware of the dimension of the problem. It was not given much priority. In the end, the best policy is control and prevention measures. Reduce risk spaces, control animal populations, inform the citizenship…
P. With so many cases for so many years, a lot must have been learned from this outbreak, right?
R. Yes. We have discovered that rabbits and hares can act as a reservoir for the parasite and we have a good understanding of the transmission dynamics. This gives us very valuable information to prevent similar outbreaks in other spaces. Regarding patients, we have seen the high susceptibility of immunosuppressed people: they are 100 times more likely to develop the visceral form than a healthy person. Even with immunity levels that are not too low. And we have also improved the clinical management of these patients with all these years of follow-up.
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