Acanthamoeba castellanii: High antibody prevalence in racially and ethnically diverse populations Neil Brindley a,b , Abdul Matin b , Naveed Ahmed Khan c, * a Department of Biology, Lambeth College, UK b School of Biological and Chemical Sciences, Birkbeck College, University of London, UK c School of Veterinary Medicine and Science, University of Nottingham, College Road, Sutton Bonington, Leicestershire, LE12 5RD, England, UK article info Article history: Received 15 October 2008 Received in revised form 17 November 2008 Accepted 23 November 2008 Available online 3 December 2008 Keywords: Acanthamoeba Epidemiology Prevalence Protozoa abstract Acanthamoeba is an opportunistic protozoan pathogen that can produce keratitis and rare but fatal enceph- alitis. In the present study, we examined secretory IgA antibody to Acanthamoeba castellanii of the T4 geno- type in mucosal secretions from 114 individuals of 37 countries, inhabitants and/or visitors, aged 16–65 years in London, UK. Acanthamoeba antibody prevalence rate was more than 85%, without any significant differences between males (86.2%) and females (89.2%). Some epidemiological factors contributing to the high prevalence of antibody to Acanthamoeba in surveyed population are discussed further. Ó 2008 Elsevier Inc. All rights reserved. 1. Introduction Acanthamoeba is an opportunistic protozoan pathogen that is widely distributed in the environment. Acanthamoeba is a recog- nized agent of two human diseases: a rare granulomatous amoebic encephalitis, limited mostly to immunocompromised individuals, that almost always results in death and a vision-threatening kera- titis, associated with the contact lens use (reviewed in Marciano- Cabral and Cabral, 2003; Khan, 2006; Visvesvara et al., 2007). Over the last few decades, there has been an increase in the number of infections due to Acanthamoeba (Khan, 2006). This is partly due to (i) growing numbers of immunocompromised individuals and con- tact lens wearers, (ii) increased awareness of free-living amoebae as potential pathogens, and (iii) the potential of Acanthamoeba to harbour pathogenic bacteria (reviewed in Marciano-Cabral and Cabral, 2003; Khan, 2006; Visvesvara et al., 2007). Given the free-living nature of these organisms, it is anticipated that we encounter Acanthamoeba during our normal lives. To demonstrate our common exposure to this ubiquitous proto- zoan, by determining anti-Acanthamoeba antibody titres in healthy populations, only a handful surveys have been conducted (Cursons et al., 1980; Cerva, 1989). In one survey of asymptomatic individu- als in the New Zealand, it was found that normal human sera from 100% of individuals tested, contained antibodies with titres ranging from 1:20 to 1:80 for Acanthamoeba spp. (Cerva, 1989). However, in other surveys that tested the presence of anti-Acanthamoeba antibodies in inhabitants of Bohemia, Czechoslovakia, it was found that out of 282 individuals, only 9 (3.2%) were seropositive (Cur- sons et al., 1980). The titres of positive sera were never higher than 1:80. In addition, 448 patients of a hospital in Prague were tested, and 41 (9.1%) were found to be positive (Cursons et al., 1980). Again, the titres of positive sera were never higher than 1:80. This study was further expanded to include patients who had central nervous system disorders. Out of 274 patients of psychiatric hospi- tal, 9 (3.3%) were positive and the highest titres of positive sera were 1:160. Interestingly, out of 50 hepatitis A patients, 26 (52%) were found to be positive for Acanthamoeba with the highest titres of positive sera being 1:640. Overall, these findings showed con- flicting results of our exposure to Acanthamoeba in the asymptom- atic population. Later studies tested the presence of Acanthamoeba antibodies in 43 healthy individuals and 25 patients of Acantha- moeba keratitis (Alizadeh et al., 2001; Walochnik et al., 2001). It was interesting that all tested individuals were seropositive for Acanthamoeba, however keratitis patients demonstrated signifi- cantly lower levels of sIgA compared with the healthy subjects. Here, we investigated the presence of anti-Acanthamoeba antibod- ies in asymptomatic individuals from diverse racial and ethnic backgrounds. 2. Materials and methods All chemicals were purchased from Sigma Laboratories (Poole, Dorset, England), unless otherwise stated. 0014-4894/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.exppara.2008.11.009 * Corresponding author. Fax: +44 115 951 6440. E-mail address: naveed.khan@nottingham.ac.uk (N.A. Khan). Experimental Parasitology 121 (2009) 254–256 Contents lists available at ScienceDirect Experimental Parasitology journal homepage: www.elsevier.com/locate/yexpr