Probable Transmission of SARS-CoV-2 from African Lion to Zoo Employees, Indiana, USA, 2021

Abstract

We describe animal-to-human transmission of SARS-CoV-2 in a zoo setting in Indiana, USA. A vaccinated African lion with physical limitations requiring hand feeding tested positive for SARS-CoV-2 after onset of respiratory signs. Zoo employees were screened, monitored prospectively for onset of symptoms, then rescreened as indicated; results were confirmed by using reverse transcription PCR and whole-genome virus sequencing when possible. Traceback investigation narrowed the source of infection to 1 of 6 persons. Three exposed employees subsequently had onset of symptoms, 2 with viral genomes identical to the lion's. Forward contact tracing investigation confirmed probable lion-to-human transmission. Close contact with large cats is a risk factor for bidirectional zoonotic SARS-CoV-2 transmission that should be considered when occupational health and biosecurity practices at zoos are designed and implemented. SARS-CoV-2 rapid testing and detection methods for big cats and other susceptible animals should be developed and validated to enable timely implementation of One Health investigations.

Keywords: African lion; COVID-19; Indiana; One Health; RT-PCR; SARS-CoV-2; United States; biosecurity; coronavirus disease; rapid test; respiratory infections; risk factor; severe acute respiratory syndrome coronavirus 2; vaccine-preventable diseases; viruses; zoonoses.

Figure 1

Traceback and forward contact tracing investigations of SARS-CoV-2 transmission between an African lion and zoo employees, Indiana, USA, 2021–2022. The traceback investigation narrowed the potential source of the lion’s SARS-CoV-2 infection to 6 zoo employees who had lion contact within 10 days, 1 of whom (employee Z5) had cranial contact within 5 days of the lion’s illness onset but did not have close contact with employees Z1, Z2, or Z3. Possible human sources were identified for Z1 (close occupational contact with Z7) and for Z3 (community activity), although in neither case were these potential sources shown to carry the virus. Employees Z1, Z2, and Z3 all had symptoms and had confirmed SARS-CoV-2 infection 3 days after their most recent cranial contact with the sick lion.

Figure 2

Timeline of probable transmission of SARS-CoV-2 from an African lion to zoo employees, Indiana, USA, 2021–2022. The lion’s likely exposure period was December 8–17, and his infectious period was December 16 through euthanasia on December 23. During the lion’s infectious period, employees Z1 and Z2 each had a single day of cranial contact with him, coinciding with the day of the lion’s illness onset. Z3 had cranial contact with the lion on 3 occasions during his infectious period. Figure highlights the lack of overlap between Z1 and Z2’s infectious period and the lion’s exposure period, and between Z3′s infectious period and Z1 and Z2’s exposure periods.

Figure 3

Phylogenetic tree of SARS-CoV-2 Delta variant, AY.103 lineage, genome sequences from an African lion (day 1 and day 5) and 2 zoo employees (Z1 and Z2) shown in comparison with reference sequences from COVID-19 patients from 7 counties in Indiana, USA, August 2021–February 2022. Reference sequences are labeled chronologically as S1 to S10. Stars indicate specimens collected in December 2021.