Sucking lice are highly host-specific ectoparasites, particularly on primates withmost lice species occurring only on a single species of host. Lice are found onprosimians, New World monkeys, Old World monkeys, and apes. The genusPediculus is found naturally on humans (Homo sapiens), bonobos and chimpanzees(Pan), howler monkeys (Alouatta), spider monkeys (Ateles), and capuchin monkeys(Cebus). This chapter concentrates mainly on the presence of Pediculus spp. in howlermonkeys to provide information on the potential louse host switch between humansand Neotropical primates. Although studies on lice in New World monkeys are veryscarce and outdated, after a thorough review we found P. mjobergi reports for threespecies of howlers: Alouatta caraya, Alouatta guariba, and Alouatta belzebul. Geneticand paleontological evidence suggest that an interchange of genetic materialbetween humans and howler lice occurred during encounters for example for subsistence or pets, probably when modern humans moved out of Africa and enteredthe Americas, and that P. mjobergi, may be an evolutionary lineage of P. humanusFil: Quijano, Romina Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Gilles, Debora Rócio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Stefka, Jan. University of South Bohemia; República ChecaFil: Kowalewski, Miguel Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; Argentin