The case of malaria in Verona has rekindled the fear that the disease – eradicated in the 1970s – could also resurface in our country. Fortunately, the health authorities have reconstructed that it is not a local case, but the news has rekindled attention on the risk associated with mosquito bites. The fear that we may witness a return to Italian territory of plasmodium (the microorganism that causes malaria) is not entirely unfounded: the species of mosquitoes that act as vectors for it are being found more and more often in our country too.
Native cases
Thousands of cases of malaria are recorded in Europe every year. In 2022, for example, there were more than 5,300, of which 99.8% linked to travel to countries where the disease is still endemic today. In Italy between 2013 and 2017 there were 3,800 cases of malaria, and eight deaths. Of these, 12 were classified as infections of autochthonous origin, i.e. not having been contracted outside national borders. However, there are three different modes of autochthonous infection, with very different meanings on an epidemiological level.
The first is that of induced cases, i.e. caused by transfusions, transplants or nosocomial infections, in which the plasmodium is taken from a patient (who perhaps contracted the disease in an area where it is endemic) in its infectious phase and then transmitted to another person. The second are the so-called cases of “airport malaria”, linked to mosquitoes that reach Italy by chance traveling on a plane or in a traveller’s suitcase, and once here they infect someone. The majority of indigenous cases in Europe follow one of these two infection routes, and therefore do not indicate the presence of active transmission of the pathogen on our territory.
A third possibility, obviously, is that the infection is instead due to the bite of an infected mosquito present on Italian territory, and therefore that there is an active transmission chain. However, to become endemic again, malaria would need two things: a sufficient number of infected people to act as a reservoir for plasmodium, and mosquitoes capable of transmitting them from one patient to the next. And if you look closely, there is no shortage of the latter in Italy either.
Mosquitoes
Malaria in Italy was declared eradicated in 1970, following a massive campaign of reclamation and disinfestation of endemic areas with the use of insecticides (mainly DDT), which led to the extinction of the mosquito species vectoring the microorganism. In fact, there are many species of plasmodium that can cause forms of malaria in humans, and even more species of mosquitoes, of which only a few (all belonging to the species Anopheles) are suitable as intermediate hosts of the microorganism, and can therefore contribute to the transmission of the disease.
With the disinfestations and reclamations of the last century, the mosquito species most suitable for the transmission of plasmodium have disappeared in Italy, and over time this has allowed the disease to be eradicated. But there continue to be several native species of mosquitoes Anophelesboth in Italy and in Europe, several of which are potentially capable of fueling a new epidemic. Research by the Istituto Zooprophylattico Sperimentale delle Venezie in 2021 recorded four in the Po Valley area, one of which, Anopheles antroparvus (fortunately found in a few specimens) which is a known vector of the disease in Northern Europe.
The Verona case must be a reminder to us: it is important to never let our guard down, even in the face of diseases that we believe have now been defeated. In fact, globalization guarantees ample opportunities for malaria plasmodium to enter our country (as certified by thousands of imported cases that are recorded every year), given that in many areas of the world it continues to represent a dramatic public health problem, which causes almost 250 million cases and more than 600 thousand deaths every year.
And climate change works in concert, to reintroduce and expand the range of mosquitoes Anopheles which can become a vector for the disease: in September 2022, for example, in Puglia a specimen of mosquito from the Maculopennis complex (the group of Anopheles that transmit malaria), and more precisely the species sacharoviknown for having been the main malaria vector in our country in the past, and for still being so today in Mediterranean areas such as Turkey.