Detection and Molecular Characterisation of Zoonotic Enteric Pathogens in Animals and Humans in Southern India

Priya, R (2011) Detection and Molecular Characterisation of Zoonotic Enteric Pathogens in Animals and Humans in Southern India. Doctoral thesis, The Tamil Nadu Dr. M.G.R. Medical University, Chennai.

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Pediatric diarrhea is a major concern worldwide. Diarrheal disease is the second most common cause of death in children under 5 years of age. There are several modes of transmission of enteric pathogens, and zoonotic transmission is known to contribute to both spread and increased diversity of putative agents. In India, although zoonotic transmission is likely to be of major public health importance, it has been poorly documented. Only a few studies have attempted to document the association between the pathogens isolated from animals and enteric infections in children. In this study, we have investigated the relative contributions of four enteric pathogens, consisting of one virus, one parasite and two bacterial species known to be common agents of diarrhea in humans and animals and their association with disease. The distribution of rotavirus genotypes in human and animal diarrheal samples indicated that based on VP7 and VP4 characterization, there were differences in the major G genotypes isolated with G6 predominating in animals and G1 in humans. However, G2 genotypes were found in both animals and humans. Since G2 genotypes are one of the major genotypes in human disease worldwide, and are not generally reported in animals, this raises the possibility of reverse zoonotic transmission. Standard typing methods for rotavirus identify only two genes for characterization of circulating strains. However, on identification of an unusual strain, G10P[15], we further characterized all 11 genes, and found evidence of possible reassortment between human, bovine and ovine rotavirus strains. In developing country settings, mixed infections with rotaviruses are frequent, resulting in reassortment and the emergence of novel rotavirus strains which can spread globally. Hence reports of such unusual strains underlines the need for frequent surveillance of domestic animals as they may be potential reservoirs for disease in the human population. Cryptosporidial species from both animal and human population were also compared in this study to investigate zoonotic transmission. We detected C. hominis as the sole species in children hospitalised with diarrhea, indicating that this species is associated with greater disease severity. Interestingly, C. hominis was also identified in one animal further supporting the possibility of reverse zoonotic transmission in this setting. The major species identified in animals was C. andersoni. This species has been reported in animals from India and other parts of the world and appears to be an important cause of diarrhea in infected animals. However, it has also been reported in human infections, and is likely to be zoonotic. We report C. xiaoi for the first time in India in three domestic animals (two cows and one goat), this species has not been previously identified in animals or humans in India, but as with other cryptopsoridial species, the potential exists for introduction into the human population in the future. Longitudinal studies in the geographical regions where animal human contact is prolonged will help in better understanding of the transmission of pathogens between species and the consequences of such infections for both clinical disease and public health. A multiplex PCR was adapted from published protocols to identify the virulence genes of DEC likely to be important causes of human disease in southern India. Using this tool, we showed that EAEC strains that lack the AA gene do not contribute to pathogenicity in pediatric diarrhea. It is of interest to note that EAEC with the AA gene were seen in animal infections indicating the zoonotic potential of this pathotype in this region. We have also documented tEPEC in animal infections for the first time in India, while other parts of country have reported aEPEC from livestock in both symptomatic and asymptomatic infections. Another interesting finding was the presence of the stx1 gene in EHEC, again indicating the possibility of zoonotic transmission. Future studies that use more intensive epidemiological tools are needed to study DEC in humans and animals to understand their role in enteric infection and their zoonotic potential. The results of the Campylobacter studies showed an association with pediatric diarrhea but mainly in conjunction with other pathogens. While other studies have reported cattle as a major reservoir of Campylobacter, we did not find these bacteria in cattle while poultry had high rates of carriage, with C. jejuni as the common species. The observation that this species was also common among human isolates is consistent with other studies where typing has indicated that strains from chickens are often linked to human campylobacteriosis. Taken together the data indicates that there is a distinct possibility of zoonotic (EHEC, EAEC and Campylobacter) and reverse zoonotic transmission (Cryptosporidium and rotavirus) in this region. Identification of unusual strains or species from animals underlines the need for continuous monitoring of livestock, since they could act as potential reservoirs of infection.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Detection, Molecular Characterisation, Zoonotic Enteric Pathogens, Animals and Humans, Southern India.
Subjects: MEDICAL > Gastroenterology
Depositing User: Subramani R
Date Deposited: 11 Jan 2022 02:55
Last Modified: 11 Jan 2022 02:55

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