Despite detecting mpox virus DNA on dogs and cats in infected households, researchers conclude the viral traces are likely from human contamination, not actual pet infections.
One Health Investigation into Mpox and Pets, United States. Image Credit: Hamara / Shutterstock
In a recent study published in the journal Emerging Infectious Diseases, a group of researchers investigated the potential susceptibility of common companion animals to Mpox virus (MPXV) (a zoonotic virus that causes the disease mpox in humans and animals) infection in households with confirmed human mpox cases.
Background
Before 2022, MPXV transmission was primarily zoonotic, linked to contact with infected wild animals in Africa. However, in spring 2022, the clade IIb variant began spreading through direct human contact, particularly within sexual networks outside endemic regions. Despite concerns about human-to-animal transmission, the current outbreak has confirmed no MPXV infections in domestic animals like dogs or cats. The Centers for Disease Control and Prevention (CDC) advises mpox patients to avoid animal contact, but further research is needed to assess the susceptibility of companion animals to MPXV and the potential for reverse-zoonotic transmission.
About the study
The CDC Multi-National Mpox Response's One Health Team collaborated with state and local jurisdictions to study the susceptibility of companion animals to MPXV infection. Investigators collected blood and swab samples from companion animals in homes where a person had probable or confirmed mpox during the infectious period. They also collected animal-associated environmental (AAE) samples to assess potential contamination from human cases. Sampling took place within 21 days of direct contact with the infected individual.
The study was conducted between July 2022 and March 2023 in the District of Columbia, Minnesota, Virginia, and Tennessee. Follow-up sampling occurred 3-4 months later to assess immune responses.
State and local public health personnel interviewed mpox patients who voluntarily participated after providing verbal consent. A questionnaire gathered information about the human case, the animal's health, household details, and the nature of contact between the infected person and the animals. The CDC reviewed the project and determined it was a nonresearch public health surveillance effort.
Animal handling and sampling followed CDC protocols, and swabs were collected from the animals' fur, oral cavity, and other areas. Samples were tested for MPXV Deoxyribonucleic Acid (DNA) using real-time polymerase chain reaction (PCR), and viral cultures were performed on PCR-positive swabs. Blood samples were collected from cooperative animals for serologic testing to detect orthopoxvirus antibodies. The study also included statistical analyses to determine correlations between MPXV DNA presence, human DNA contamination, and factors such as household size and animal contact behaviors.
Study results
The study sampled 34 companion animals from 21 households, including 24 dogs, 9 cats, and 1 rabbit. The animals' ages ranged from 4 months to 16 years, and they were evenly divided between male and female. Most households had a single human mpox case, while one household had two. A total of 191 animal swabs and 56 animal-associated environmental (AAE) specimens were collected. Skin lesions were observed in 6 dogs and 1 cat during the examination.
PCR testing revealed MPXV DNA in samples from 5 animals (4 dogs and 1 cat) from 4 households. Overall, 12% of animal swabs tested positive for MPXV, with a significant correlation (p<0.01) observed between MPXV DNA and human DNA contamination. The majority of MPXV-positive animal samples were also positive for human DNA, with Ct values showing a strong correlation between MPXV and human DNA. This finding suggests that the MPXV DNA detected in animal samples was likely due to contamination rather than true infection.
No MPXV DNA was detected in any blood specimens, and viral culture attempts failed to produce viable virus from PCR-positive samples. Additionally, none of the serum specimens collected during the study showed any presence of orthopoxvirus (OPXV) antibodies. Three of the MPXV-positive animals did not have blood samples taken due to noncompliance or aggression, and follow-up samples were unavailable.
Among the AAE samples, 29% of households tested positive for MPXV DNA, and 25% of AAE specimens tested positive. A statistically significant correlation (p<0.05) was found between the presence of MPXV DNA in AAE samples and human DNA presence, further supporting the likelihood of contamination from human cases. All four households with MPXV-positive animal samples also had MPXV-positive AAE samples. The correlation between MPXV and human DNA Ct values in these samples further reinforced the conclusion of contamination.
The study also identified a significant negative correlation (p<0.05) between household size and the prevalence of MPXV DNA in animal and environmental samples, suggesting that smaller living spaces may increase the risk of contamination. However, larger households had a significantly lower prevalence of MPXV and human DNA in animal and environmental samples, which may indicate that household size influences the degree of contamination or exposure.
Conclusions
To summarize, in the study of households, MPXV DNA was found on some dogs, cats, and environmental samples, but no live virus or antibodies were detected, suggesting contamination from infected humans rather than true infection. The statistical analyses conducted in the study strongly support the conclusion that the MPXV DNA detected in companion animals resulted from environmental contamination from human cases, not true infections. No confirmed MPXV infections in pets were identified. The CDC recommends limiting pet interactions during mpox infection to prevent potential virus spillback.
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