SARS-CoV-2: preliminary study of infected human nasopharyngeal tissue by high resolution microscopy.

Background: The novel coronavirus SARS-CoV-2 is the etiological agent of COVID-19. This virus has become one of the most dangerous in recent times with a very high rate of transmission. At present, several publications show the typical crown-shape of the novel coronavirus grown in cell cultures. However, an integral ultramicroscopy study done directly from clinical specimens has not been published.

Methods: Nasopharyngeal swabs were collected from 12 Cuban individuals, six asymptomatic and RT-PCR negative (negative control) and six others from a COVID-19 symptomatic and RT-PCR positive for SARS CoV-2. Samples were treated with an aldehyde solution and processed by scanning electron microscopy (SEM), confocal microscopy (CM) and, atomic force microscopy. Improvement and segmentation of coronavirus images were performed by a novel mathematical image enhancement algorithm.

Results: The images of the negative control sample showed the characteristic healthy microvilli morphology at the apical region of the nasal epithelial cells. As expected, they do not display virus-like structures. The images of the positive sample showed characteristic coronavirus-like particles and evident destruction of microvilli. In some regions, virions budding through the cell membrane were observed. Microvilli destruction could explain the anosmia reported by some patients. Virus-particles emerging from the cell-surface with a variable size ranging from 80 to 400 nm were observed by SEM. Viral antigen was identified in the apical cells zone by CM.

Conclusions: The integral microscopy study showed that SARS-CoV-2 has a similar image to SARS-CoV. The application of several high-resolution microscopy techniques to nasopharyngeal samples awaits future use.