Transmission and detection of monkeypox virus in saliva: Implications for dental practice and public health

A monkeypox virus (MPXV) outbreak has been ongoing nonendemic countries since May 2022, and it was declared a public health emergency of international concern by the World Health Organization.¹ Human-to-human transmission of MPXV occurs frequently, especially among men who have sex with men. So far, several papers have been published in oral and maxillofacial journals regarding case description^2,3 and the implications of monkeypox in clinical dental care.^{4, 5, 6, 7, 8} All of them focus on oral and maxillofacial manifestations, patient screening and management, and awareness of protective measures. Oral and maxillofacial workers should note that premonitory signs of the disease usually appear on the oral mucosa as macules and ulcers and lymphadenopathy in maxillary, submandibular, and cervical lymph nodes during the prodromal period.^{2, 3, 4, 5, 6, 7, 8} Meanwhile, the workers should note the risk of its occupational transmission in dental practice, due to MPXV within oral fluids (sputum or saliva); while saliva as a fluid specimen for transmission and detection of monkeypox virus is not seemingly highlighted in the journals.^{4, 5, 6, 7, 8}

We performed a rapid literature review on bodily fluids of MPXV-DNA detection to better understand the possible role in disease transmission. Among bodily fluids and swabbed samples, attention is thus focused on the use of sputum or saliva as a sampling material for MPXV diagnosis. Peiró-Mestres et al.⁹ recently reported that MPXV were positive in all the saliva samples from 12 cases studied, and in some cases, at low quantification cycle values indicative of high viral loads. However, MPXV were not positive in all the other bodily fluids and swabbed samples: rectal swab (11/12 cases), nasopharyngeal swab (10/12 cases), semen (7/9 cases), urine (9/12), and faeces (8/12 cases).⁹ Although testing specimens from multiple samples may improve the sensitivity and reduce false-negative test results, saliva test is plausible of highest sensitivity. In addition, MPXV could be positively tested in saliva samples collected since 3 or 4 days after the onset of symptoms, while it was tested in other fluid samples collected since 5 or 6 days after the onset of symptoms.^9,10 These results suggest saliva as an emerging potential sample for rapid and accurate diagnosis of MPXV.

Diagnostic testing of MPXV is vital in containment of the disease in hospital and community settings. Although skin swabs from vesicles, ulcers or crusted lesions are the standard samples used for MPXV test, skin lesions may be scarce, located only in the anogenital area or even limited to a single lesion, and asymptomatic infections are also existed in monkeypox patients. There is few information on the role that different samples may have in the diagnosis of symptomatic or pre-/asymptomatic virus infection period.^4,5 Although saliva is also one of vectors in the human-to-human transmission, salivary diagnostics may provide a convenient, non-invasive, and cost-effective platform for MPXV detection. Notably, obstacles to collection include lack of swabs and transport media, the need for skilled staff and personal protective equipment for swabs collection.

Importantly, saliva can be self-collected easily, as patients spit into a sterile container in ambulatory areas, and sample collection can be not dependent on the expertise of collectors. Saliva specimen can be collected where negative ventilation chambers are not available such as in community and household areas. This greatly minimizes the exposure of healthcare workers to the virus and the risk of cross infection. Also, suitably supervised saliva collection is undoubtedly simpler and more comfortable than using swab collection, which usually needs a skilled staff with personal protective equipment to perform it. These findings are highly relevant in the face of shortages of both swabs and personal protective equipment in many settings.

Considering the similarity of virus in oral fluid, we speculate that there is a couple of different pathways for MPXV to present in saliva. Firstly, a possible pivotal way for MPXV to occur in the oral cavity is via minor- and major-salivary gland infection, with subsequent release of virus particles in saliva via salivary ducts. Secondly, oral mucosal cells from the macules and ulcers and lymph from maxillofacial and cervical lymphadenopathy infected by the MPXV that enters the oral cavity together with the liquid droplets frequently exchanged by these organs. Additionally, MPXV may present in the blood can access the mouth via gingival crevicular fluid that contains local proteins derived from serum-derived proteins. However, data on the utility of saliva for MPXV are quite minimal. Besides, there is seeming lack of standard operation procedure collection methods: whole unstimulated saliva in tube, coughing to generate saliva-sputum mixtures, or dilution in viral transport media. Consequently, this letter also highlights the need to optimize saliva collection and processing before saliva can be used for high volume testing.

Taken together, dentists and maxillofacial specialists should keep an eye out for oral and maxillofacial manifestations of monkeypox infection and protective measures. Furthermore, special attention is focused on the use of saliva as a sampling material for diagnosis of monkeypox infection. Saliva may emerge as a viable sample for diagnostic and public health goals for MPXV testing, superior to swabbed samples for screening pre-/asymptomatic infections with scarce lesions and also desirable for sequential monitoring of viral load. Further investigations are needed to obtain a coherent understanding of salivary diagnostic and transmission of MPXV, which is crucial to improve effective strategies for prevention.

Declaration of competing interest

The authors have no conflicts of interest relevant to this article.