Prevalence and Level of Antibodies Anti-Plasmodium spp. in Travellers with Clinical History of Imported Malaria

In this study, we show that 40.29% of travellers with a possible history of malaria exposure were positive for anti-Plasmodium spp. antibodies, while these individuals were negative by microscopy. The antibody test described here is useful to elucidate malaria exposure in microscopy-negative travellers from endemic countries. 1. Introduction Malaria is an infectious disease caused by a protozoan parasite of the genus Plasmodium, which is transmitted between humans by the bite of infected female Anopheles mosquitoes. These parasites have a complex life cycle, both in the invertebrate vector and vertebrate hosts. In the human body, parasites multiply in hepatocytes, and then invade red blood cells (RBCs), initiating blood stage infection, which corresponds to the symptomatic period of the disease [1]. Malaria remains one of the most serious public health problems not only in endemic countries, where 2 billion people (approximately 40% of the world’s population) are at risk of contracting the disease, but also in nonendemic areas, where the increasing number of imported malaria cases is worrying [2]. In developed countries, imported malaria predominates in tourists and immigrants who travel to their home countries to visit friends and relatives. Every year, approximately 125 million international travellers visit malaria endemic areas, and 30,000 of them contract the disease [3, 4]. In Portugal, the occurrence of 50 such cases per year [5] is estimated according to the National Public Health System. Following infection with any of the five species of Plasmodium that are capable of infecting humans, P. falciparum, P. ovale, P. vivax, P. malariae, and P. knowlesi, specific antibodies are produced one or two weeks after the initial infection and persist for three to six months after parasite clearance [6]. These antibodies may endure for months or years in semi-immune patients in endemic countries where reinfection is frequent. However, in a na？ve patient, antibody levels fall more rapidly. Reinfection or relapse leads to a secondary response with a high and rapid rise in antibody titres [6, 7]. Thus, in the present study, we aim to evaluate the prevalence and the level of anti-Plasmodium spp. antibodies in serum samples from travellers with possible clinical signals and symptoms of malaria. Using an ELISA-based commercial immunoassay kit to measure antimalarial antibodies, we determined the raw serological profile of these individuals. Additionally, we compare the latter serological profile with the gold-standard laboratory diagnosis, based on direct