Giovanni Rezza, MD: Tropical Outbreaks in Temperate Regions Are on the Rise

At the European Congress for Clinical Microbiology and Infectious Diseases (ECCMID 2019), Giovanni Rezza, MD, presented in a symposium on the potential impact of climate change on the growth of water-borne and vector-borne infections. Rezza, the head of infectious diseases at Superiore di Sanità in Italy, sat down with Contagion® to recap his presentation on the rise of tropical outbreaks in temperate climates.

Interview transcript (modified slightly for readability):

Contagion®: Your presentation is titled Tropical Outbreaks in Temperate Areas. Can you provide some background on the trend and provide some examples?

Rezza: Tropical outbreaks are becoming not unusual in temperate areas, especially in the Mediterranean area of Europe. Actually, the first major outbreak occurred about 11 years ago. It was the end of August when I received the call from a place in northeastern Italy where they asked us to intervene because they had more than 50 cases of a strange disease. So, I decided to go there; it was still hot and humid, so the climate was like the climate of a part-time tropical country, and I visited some patients and then we visited also the epicenter of the outbreak. We found a lot of Asian tiger mosquitoes, this was in the northeast of Italy, so it was not unexpected because the tiger mosquito established in Italy many years ago at the beginning of the 1990s, but having a strange outbreak of an unknown disease was not usual.

So, I visited some patients, we found the tiger mosquito. The first case was an Indian guy coming from Kerala, so I hypothesized that it could be a tropical disease. Actually, the first diagnosis was suspected chikungunya and the alternative diagnosis was dengue. We examined some samples we found positivity for chikungunya, so we realized that for the first time in Europe, we had an emergency due to chikungunya, a tropical virus.

Ten years later, again in Italy, in a place not far away from Rome, we had another major outbreak of chikungunya with a secondary outbreak in the south of Italy. So, this means that in the era of globalization when men and microbes go around the world and they may reach every part of the world in just a few hours, you may have tropical diseases occurring in temperate areas if the vector is there. And, we had the vector, we have globalization, so microbes may move around causing outbreaks of tropical diseases.

Then in Europe, we had also other outbreaks, for example, an outbreak of dengue in Croatia on the Dalmatian coast and clusters of dengue and chikungunya in the South of France in Spain and in the island of Madeira that is Portuguese. So, this means that every year we face tropical clusters or tropical or cases or tropical outbreaks, sometimes major outbreaks, and we had to do something to contrast these emergencies.

Contagion®: What is the impact of climate change on infectious disease?

Rezza: This is not still well-defined because, actually, we are talking of tropical diseases occurring during the summertime in places that are already that have already hot and humid summer — what I call part-time tropical countries. Then usually, the winter arrives, and mosquitoes go to rest, the activity of mosquitoes goes down, and the outbreak usually stops. The point is that the higher the temperature and the higher the humidity, the higher the risk of having these kinds of outbreaks if the vector is there and if the microbe is there. Climate is changing, and the summer is becoming warmer and also more humid and this may favor may contribute to mosquito density that is increasing.

The other point is if summertime becomes longer and longer then the number of cases can accumulate, and you may have a major outbreak. We don't know whether the summers may become so long that an endemic cycle transmission may establish — up to now this is not possible because anyway when the winter arrives, the activity of the mosquitoes goes down. But there are not only vector-borne diseases that have been identified in the south of Europe, for example, we had also a cluster of cases of schistosomiasis – that is typically a tropical parasitosis – in Acosta, a French island, so we are dealing with different kinds of tropical viruses and parasites and we have to intervene earlier in order to contrast.

Contagion®: How can this issue be corrected?

Rezza: Actually, 1 of the major problems we had when we face these outbreaks was that early diagnosis was not done, because it's unexpected to have cases of dengue or chikungunya or schistosomiasis or even a local transmission of the Plasmodium vivax malaria, as it happened also in Greece. So, when you have this kind of disease usually if you go today general practitioner they don’t think that maybe a tropical disease and so the outbreaks go on and the number of cases increases, and that's the major problem. What we had to do is to train doctors in order to get an early diagnosis as soon as the first cases occur in order to implement an intervention that may be, for example, mosquito control intervention or whatever other interventions should be done.

The presentation, “Tropical outbreaks in temperate areas,” was given in a symposia session on Sunday, April 14, 2019, at ECCMID 2019 in Amsterdam, the Netherlands.