Leishmaniosis is a parasitic zoonotic disease caused by a protozoan of the genus Leishmania. It is an endemic disease in 98 countries including the Mediterranean basin, South America, Asia, Africa and the United States.
The microorganism present in the Mediterranean area and particularly in Spain is Leishmania infantum. In Spain the main reservoir is the dog, although the parasite has been detected in other animals such as cats, lagomorphs, rodents and birds.
Leishmaniosis is transmitted by the bite of an infected vector, although some cases of congenital, parenteral, sexual and interpersonal transmission have been described.
There are three main clinical forms of leishmaniosis: cutaneous, mucocutaneous and visceral. Visceral leishmaniosis or kala-azar is endemic, among other regions, in the Mediterranean basin and it is the most severe form of disease, presenting a high mortality rate when untreated.
The leishmaniosis vector is an dipteran insect called phlebotomine or sandfly. It is 1.5mm-3.5mm in length, has a yellowish colour and has hair covering the whole body, including the wings.
Both males and females use sugary substances of plants and floral nectar to survive; however only the females can transmit the disease since they are hematophagous, and they need blood to produce their eggs.
The activity cycle in sand flies begins at dusk and continues during the first hours of the night, and at dawn. During the day they are not visible, remaining in cracks and land crevices, such as of tree hollows, landfills, sewers, ruined houses, etc. In the Mediterranean area they prefer warm nights (above 16 ° C). They are too small to fly in strong winds (exceeding 1 m/s). However, they can travel over long distances (2 Km). Rain is another factor that makes their flight difficult. They feel extremely attracted to light. Humidity is also a factor influencing the increased survival of mosquitoes.
Sandlies habitats are usually rural areas or places with trees in cities, such as gardens and parks. They mainly bite outdoors, although they can also live inside a house. They find the feed thanks to the body odor that reaches them through the air currents.
Phlebotomine sandflies have a seasonal activity starting with the first heats of May and ending in September or October. In winter the sandflies remain in Quaternary larval stage. However, the gradual increase of temperatures caused by the climate change is leading to a proliferation of phlebotomines, thus being possible to find active specimens all over the year in the Mediterranean basin.
In Spain more than a dozen species of sandflies have been described, among which only two are effective reservoirs of the disease (Phlebotomus perniciosus and P. ariasi).
Leishmaniosis risk factors are linked to the human development, such as massive emigration from the countryside to the city, agro-industrial projects and the environmental changes produced by man (creation of swamps, irrigation systems and wells).
Susceptibility to the disease is generalized, but children and inmunocompromised people (immunosuppresive treatments, hematologic disorders, cancer, HIV seropositives, autoimmune diseases) develop the disease more frequently. Even though anyone can be infected in an endemic area, it is unlikely that a healthy person develops the disease since the immune response is very strong and effective.
The distribution area of leishmaniosis is not only conditioned by the simple presence of the vector, but also by its number: below a certain density of the vector, maintaining the stability of the infection is not easy.
The human host, the parasite, the vector, and the animal reservoir are all involved in the leishmaniosis transmission. Competent vectors are distributed throughout the Iberian Peninsula and the Balearic Islands, and therefore the risk of Leishmania transmission may occur in any area, if the appropriate conditions arise.
It is necessary to strengthen the disease surveillance in order to be able to detect new cases as early as possible. Besides, an entomological surveillance network is crucial in order to assess the evolution of the infection rates of the vector, and an epidemiological surveillance network would be of benefit in all the autonomous communities in order to identify as quickly as possible the vectors and reservoirs involved in the transmission in each particular area, in order to be able to respond with appropriate measures.
The best form of prevention is to avoid mosquito bites.
Nowadays, demographic, environmental, climatic and urban changes are leading to a modification in the disease distribution in Europe. It is expected that global warming and the Earth degradation will affect the epidemiology of leishmaniosis. Firstly, the changes in the temperature, precipitation and humidity can have large effects on the ecology of the vectors and reservoirs, changing their distribution and playing a role in their survival and also in the population size. Secondly, small temperature changes can have huge effects on the life cycle of Leishmania promastigotes in the sandfly, enabling the transmission of the parasite in areas in which the disease was not endemic. Cases of leishmaniosis described in the North of Italy, the North of Spain and central France illustrate this situation. In addition, the mobility of people and animals allows that many leishmaniosis cases appear in the Netherlands, Germany, Hungary and Central France which are imported by dogs adoption or travel to endemic areas.
Moreover, the spread of exotic Leishmania species is already a reality; recent cases of L. donovani, L. tropica and L. major in dogs in the eastern part of the Mediterranean basin have been described.
This new epidemiological situation requires further studies and an update on diagnostic techniques because if these methods are only focused on the detection of L. infantum the role of exotic species could be underestimated is our scenario.
Laboratory studies have shown that many species of sandflies are capable to adapt to the development of different species of Leishmania (with the exception of two specific vectors: P. patatasi with L. major and P. sergenti with L. tropica). At the same time, Leishmania species may adapt to other vectors (i.e. L. infantum with Lutzomyia longipalpis in Latin America).
It is clear that the epidemiology of leishmaniosis is changing in Europe and therfore an increase in the number of cases in humans and animals would not be a surprise. European health authorities need to implement measures of control. At the same time, doctors and veterinarians should be aware of the problem and should learn to recognize the symptoms of the disease, especially in areas where is is not common. In Spain, the information collected by the national network of epidemiological surveillance (RENAVE) is essential to identify priorities and to better understand the risk perception. Therefore, it is necessary to strengthen surveillance in order to detect, as early as possible, new leishmaniosis cases and to ensure that the necessary information is collected in order to carry out a proper risk management.
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