Pet dogs—A transmission route for human noroviruses?

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Abstract

Background

Human noroviruses (HuNoVs) are one of the leading causes of diarrhoeal diseases worldwide in all age groups. Virus transmission can occur via the faecal-oral route from person to person or via contaminated food, water, or surfaces. The most common NoV strains circulating among humans belong to genogroup GII. Thus far, to our knowledge, no HuNoVs have been detected in pets.

Objectives

We investigated whether pet dogs could serve as carriers for HuNoVs and thereby transmit the infection to humans.

Study design

Ninety-two faecal samples of indoor pet dogs were obtained. The main criteria for sample collection were that the dog or humans in the household had suffered from diarrhoea or vomiting. All samples were screened for HuNoV genogroups GI, GII, and GIV by real-time one-step RT-PCR.

Results

We detected HuNoV in four faecal samples from pet dogs that had been in direct contact with symptomatic persons. Three of the positive samples contained genotype GII.4 variant 2006b or 2008 and one GII.12. All NoV-positive dogs lived in households with small children and two dogs showed mild symptoms.

Conclusions

Our results suggest that HuNoVs can survive in the canine gastrointestinal tract. Whether these viruses can replicate in dogs remains unresolved, but an association of pet dogs playing a role in transmission of NoVs that infect humans is obvious.

Section snippets

Background

As summarized in a recent review,1 human noroviruses (HuNoVs), members of the Caliciviridae family, are one of the leading causes of diarrhoeal diseases worldwide in all age groups. Virus transmission occurs via the faecal-oral route from person to person or via contaminated food, water, or surfaces. In an infected person, typical symptoms, such as nausea, vomiting, and diarrhoea, can appear within 12 h of virus ingestion and last for 1–3 days. In more severe cases, the infection lasts for

Objectives

The purpose of our study was to determine whether pet dogs could serve as carriers for HuNoV and thereby transmit the infection to humans either directly or by contaminating food or water.

Faecal samples

Ninety-two stool samples from 47 breeds of indoor pet dogs were obtained. The main criteria for sample collection were that the dog or humans in the household had suffered from diarrhoea or vomiting. Samples were also accepted if the dog owner was in close contact with humans with a confirmed NoV infection. All 92 samples were collected outdoors carefully avoiding any other environmental contaminants in late winter (February–April) 2009 (56 samples) and 2010 (36 samples) in southern Finland and

Results

Of the 92 canine faecal samples, 4 (4.3%) tested positive for GII HuNoVs (Table 1). The Cq values of these samples varied from 23 to 37 (mean 30.98). All of the positive samples were collected from dogs living in households with more than two symptomatic persons suffering from vomiting, fever, and diarrhoea lasting 1–3 days. The two symptomatic dogs with HuNoV in their faeces suffered from nausea and loss of appetite for one day; one of these dogs also vomited once. As Fig. 1 shows, HuNoVs were

Discussion

Our results show that HuNoV genome can remain intact in the canine gastrointestinal tract. Thus, pet dogs can serve as carriers for HuNoVs. In Finland, HuNoV variants GII.4-2006b and GII.4-2008 were not only present in canine samples, but also commonly circulated in the human community during the epidemic seasons of 2009 and 2010 (data not shown). Our results and the close genetic resemblance of some genogroup IV NoVs found in humans to those that have been detected in dogs with diarrhoea12

Funding

This study was funded by the Academy of Finland (grant no. 1122782), the Finnish Veterinary Foundation, and the Walter Ehrström Foundation.

Competing interests

None.

Ethics committee approval

Not required.

Acknowledgements

We thank K. Söderberg, T. Kantala, M. Mattila, R. Mustonen, T. Summa, and P. Summa for their valuable contributions during sample collection.

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