Towards the comprehension of fasciolosis (re-)emergence: an integrative overview

Abstract

The increasing distribution and prevalence of fasciolosis in both human and livestock are concerning. Here, we examine the various types of factors influencing fasciolosis transmission and burden and the interrelations that may exist between them. We present the arsenal of molecules, 'adjusting' capabilities and parasitic strategies of Fasciola to infect. Such features define the high adaptability of Fasciola species for parasitism that facilitate their transmission. We discuss current environmental perturbations (increase of livestock and land use, climate change, introduction of alien species and biodiversity loss) in relation to fasciolosis dynamics. As Fasciola infection is directly and ultimately linked to livestock management, living conditions and cultural habits, which are also changing under the pressure of globalization and climate change, the social component of transmission is also discussed. Lastly, we examine the implication of increasing scientific and political awareness in highlighting the current circulation of fasciolosis and boosting epidemiological surveys and novel diagnostic techniques. From a joint perspective, it becomes clear that factors weight differently at each place and moment, depending on the biological, environmental, social and political interrelating contexts. Therefore, the analyses of a disease as complex as fasciolosis should be as integrative as possible to dissect the realities featuring each epidemiological scenario. Such a comprehensive appraisal is presented in this review and constitutes its main asset to serve as a fresh integrative understanding of fasciolosis.

Keywords: Climate change; Fasciola; environmental degradation; human activities; livestock production; neglected tropical diseases; parasite biology; poverty; water and food security.

Fig. 1.

Factors that have contributed to the rise of fasciolosis burden in the last decades. The biological features of Fasciola parasites determining their high adaptability together with the increased environmental degradation and social risk-related factors are in the core of faciolosis (re-)emergence. The increasing scientific awareness and the boosting of health policies aiming at recognizing and investigating the so-called neglected tropical diseases concomitantly with improvements in diagnosis have contributed to highlight the global burden of this largely ignored disease.

Fig. 2.

Integrative diagram showing the interrelation between biological (parasite-related), environmental and social factors directly influencing the different components participating in Fasciola spp. transmission. (1) Fasciola adult in the definitive host, (2) egg, (3) miracidium, (4, 5, 6) sporocyst development, and rediae and cercariae production in the snail host, (7) metacercariae formation following cercariae encystation, (8) water and vegetation contaminated with metacercariae.

Fig. 3.

The data compilation from searching results on Scopus (A, C) and Pubmed (B, D) databases using (i) Fasciola OR Fasciolosis OR Fascioliasis as basic search criterium, and complemented it with: (ii) AND human, (iii) AND ruminants OR livestock, (iv) AND epidemiology, (v) survey, (vi) diagnostic method OR detection method. (A, B) The absolute number of entries per year, between 1940 and 2019, for each search criteria. (C, D) The percentage of entries for each complementary criterion (from ii to vi) over the total of entries corresponding to the basic search criterion (i) in 10-year intervals.