Epidemiological and molecular evidence supports the zoonotic transmission ofGiardiaamong humans and dogs living in the same community

Abstract

S U M M A R YGiardia duodenalis isolates recovered from humans and dogs living in the same locality in a remote tea-growing community of northeast India were characterized at 3 different loci ; the SSU-rDNA, elongation factor 1-alpha (ef1-a) and triose phosphate isomerase (tpi) gene. Phylogenetic analysis of the SSU-rDNA and ef1-a genes provided poor genetic resolution of the isolates within various assemblages, stressing the importance of using multiple loci when inferring genotypes to Giardia. Analysis of the tpi gene provided better genetic resolution and placed canine Giardia isolates within the genetic groupings of human isolates (Assemblages A and B). Further evidence for zoonotic transmission was supported by epidemiological data showing a highly significant association between the prevalence of Giardia in humans and presence of a Giardia-positive dog in the same household (odds ratio 3 . 01, 95% CI, 1 . 11, 8 . 39, P=0 . 0000).

Transmission cycles of Giardia duodenalis in dogs and humans in Temple communities in Bangkok—A critical evaluation of its prevalence using three diagnostic tests in the field in the absence of a gold standard

“…These transmission cycles reflect the close association shared Page 14 of 31 A c c e p t e d M a n u s c r i p t 14 between dogs and humans, as well as the close interaction shared between dogs as pack animals in these Temple communities, which is expected in urban environments (Itagaki et al, 2005). There was however, an unusual dominance of Assemblage A genotypes of G. duodenalis in dogs as well as in humans in our study, supporting a number of previous studies (Traub et al, 2004;Eligio-Garcia et al, 2005;Itagaki et al, 2005;Lalle et al, 2005) indicating that Assembalge A may be most significant genotype when dealing with zoonotic potential. Dog-specific Assemblages C and D of G. duodenalis were also recovered from a moderate number of humans in this study.…”

“…This was a similar finding to that of Traub et al (2004) who found that humans from tea-growing communities in Assam were more likely to be infected with Giardia if they resided in a household with at least one infected dog. Age was found to be a significant risk factor for the prevalence of Giardia in humans using both IFAT and PCR, with younger humans having higher odds of infection.…”

“…Dog-specific Assemblages C and D of G. duodenalis were also recovered from a moderate number of humans in this study. Allelic polymorphism present in the SSU-rDNA gene of G. duodenalis may be a possible explanation for this and has been discussed in detail elsewhere (Traub et al, 2004). This is the first study to ascertain the prevalence and genotypes of G. duodenalis in dogs in Thailand.…”

“…Recent literature has focussed on the role of companion animals as providing the greatest risk of zoonotic transmission of G. duodenalis ( Traub et al, 2004;Eligio-Garcia et al, 2005;Itagaki et al, 2005;Lalle et al, 2005). This conclusion has largely been drawn from data showing that G. duodenalis is one of the most common enteric parasites of dogs in both developed as well as disadvantaged communities worldwide (Itoh et al, 2001;PonceMacotela et al, 2005) and that genetically identical, potentially zoonotic genotypes of G. duodenalis (predominantly Assemblage A) may exist in humans and dogs living within the same locality (Ponce-Macotela et al, 2002;Traub et al, 2004;Eligio-Garcia et al, 2005;Lalle et al, 2005) . On the other hand, non-zoonotic or dog-specific cycles of G. duodenalis transmission have also been shown to exist in dogs in communities where it is hypothesised that the frequency of transmission of Giardia among dogs is high (Hopkins et al, 1997;Itagaki et al, 2005;Palmer et al, 2008).…”

“…In humans, both immunofluorescence antibody tests (IFAT) and ELISA have also been shown to be more sensitive and specific than conventional microscopic techniques ( Addiss et al, 1991;Hopkins et al, 1993;Rashid et al, 2002) . Polymerase chain reaction (PCR) based tests are increasingly being utilised to diagnose and estimate prevalence for Giardia infections in animals and humans in the field ( McGlade et al, 2003;Traub et al, 2004;Trout et al, 2005;Ryan et al, 2005;Fayer et al, 2006) with improved sensitivity to microscopic detection and immunodiagnostic methods (McGlade et al, 2003). Previous studies have typically estimated the sensitivity and specificity of newly developed molecular or immunodiagnostic tests for Giardia by comparing them with known microscopy positive and negative samples (Cirak and Bauer, 2004;Guy et al, 2004) .…”