SC/59/DW8 Microparasites and their potential impact on the population dynamics of small cetaceans from South America: a brief review Marie-Françoise Van Bressem 1,2 , Juan Antonio Raga 3 , Thomas Barrett 4 , Salvatore Siciliano 5 , Ana Paula Di Beneditto 6 , Enrique Crespo 7 and Koen Van Waerebeek 1,2 1 Cetacean Conservation Medicine Group (CMED-CEPEC), Waldspielplatz 11, 82319 Starnberg, Germany and CEPEC, Museo de Delfines, Pucusana, Lima-20, Peru; 2 Federal Public Service; Public health, Food Chain security and Environment, International Affairs, Eurostation building, Place Victor Horta 40, box 10, B-1060 Brussels, Belgium. 3 Department of Animal Biology & Cavanilles Research Institute of Biodiversity and Evolutionary Biology, University of Valencia, Dr Moliner 50, 46100 Burjasot, Spain; 4 Institute for Animal Health, Pirbright Laboratory, Ash Road, Pirbright, Woking GU24 ONF, UK; 5 Grupo de Estudos de Mamíferos Marinhos da Região dos Lagos (GEMM-Lagos) & Laboratório de Ecologia, Departamento de Endemias Samuel Pessoa, Escola Nacional de Saúde Pública/FIOCRUZ. Rua Leopoldo Bulhões, 1480-térreo, Manguinhos, Rio de Janeiro, 21041-210 RJ Brazil; 6 Laboratório de Ciências Ambientais, UENF, RJ, Brazil; 7 Centro Nacional Patagónico (CONICET), Boulevard Brown 3600, 9120 Puerto Madryn, Chubut, Argentina. ABSTRACT We briefly review the pathology, epidemiology and molecular biology of cetacean viruses (including morbilli, papilloma and pox) and Brucella spp. encountered in South America. Antibodies against cetacean morbillivirus were detected (by iELISAs and virus neutralisation tests) in SE Pacific and SW Atlantic delphinids. Morbilliviruses are possibly enzootic in Lagenorhynchus obscurus and offshore Tursiops truncatus from Peru and in Lagenodelphis hosei from Brazil and Argentina, but no morbillivirus antibodies were found in inshore small cetaceans. Papillomaviruses cause genital warts in at least three odontocete species in Peru. Two Phocoena spinipinnis papillomaviruses (PsPVs) were found in warts of Burmeister’s porpoises; one (PsPV-1) was cloned and characterized. Half of porpoises had developed genital warts, while in 10% of males the lesions were sufficiently numerous and severe to at least hamper, if not impede, copulation. High titers of cowpox virus neutralising antibodies were detected in Peruvian D. capensis, T. truncatus, L. obscurus and P. spinipinnis in 1993-1995. The high prevalence of orthopoxvirus neutralising antibodies with high titres indicates common infection by poxviruses antigenically related to cowpox virus, the probable causative agents of tattoo skin disease. Cetacean poxviruses may cause significant mortaliy among neonates and calves unprotected by maternal immunity. In Peru, Brucella spp. antibodies were detected (competitive ELISA) in D. capensis, T. truncatus, L. obscurus and P. spinipinnis. Brucellosis is likely enzootic in the latter two species, and may lead to orchitis and bone lesions in L. obscurus and D. capensis. The enzootic circulation of brucellae in L. obscurus and P. spinipinnis may constitute a measurable limiting factor among the environmental variables affecting population dynamics. Also, widespread Brucella spp. infection in several Peruvian odontocetes has public health implications (zoonosis), considering frequent manipulation of carcases and consumption of meat. Extrinsic anthropogenic factors may not only exacerbate the consequences of viral infections on the health of a particular individual, but also operate at the population level. INTRODUCTION Evidence is mounting that microparasites, including viruses, bacteria, and protozoans, may constrain the growth of wild animal populations (Anderson and May, 1979; Anderson, 1982; Fenner, 1983; Gulland, 1995). The intensity of this effect is a function of the heightened mortality rate and/or reduction in reproductive capacity. Thus, microparasites may increase the risk of extinction of small populations in combination with other factors (May, 1986; Thorne and Williams, 1988; Gulland, 1995; Raga et al., 1997). The potential of viruses to significantly influence population dynamics of cetaceans was mostly overlooked until the advent of morbillivirus mortalities in harbour porpoises Phocoena phocoena in the NE Atlantic in 1988-1990 and of a lethal epizootic of morbillivirus in striped dolphins Stenella coeruleoalba in the Mediterranean in 1990-1992 (Kennedy et al., 1988; Domingo et al., 1990; Van Bressem et al., 1991, 1993). These mortalities have stimulated research on microparasite infections in cetaceans and stressed the need to investigate their long-term consequence. Here we summarize current understanding on the presence of cetacean morbilliviruses, 1