Introduction and Background
Initial investigations into the origin of the SARS-CoV-2 virus pointed to the animals sold at the Wuhan seafood market (Huang et al, 2020). In particular, the virus is believed to have originated from either bats, pangolins or a recombination between the virus found in bat and pangolins sold in the market (Zhou et al., 2020; Liu et al 2020). Though it is now highly doubtful whether pangolins are the original source, it is important to note that genetic comparisons have shown that the genome of the coronaviruses found in pangolins and thatof the SARS CoV-2 exhibit a genome sequence similarity of 99% (Cyranoski D 2020). By contrast, it is now highly suspected that SARS CoV-2 has its ecological reservoirs in bats. This is based on similarities in the biological features and the sequence identity between bat-nCoV and SARS-CoV-2 (Chan et al 2013; Nguyen et al, 2020: Ren et al., 2020).
SARS-Cov-2 virus is highly contagious and is transmitted between humans via respiratory droplets or close contact (Li et al., 2020). One important aspect of SARS-CoV-2 epidemiology that has received limited attention, particularly in Africa, is the transmission of the virus between humans and animals. This is important because SARS-CoV-2 is known to infect animals (Prince et al., 2021) and human to animal transmissions have been demonstrated. In addition, SARS-CoV-2 infections have been documented in cats and dogs in the UK (Smith et al., 2021), Belgium and the USA [Garigliany et al., 2020; Newman et al., 2020; Sit et al., 2020). The detection of SARS-CoV-2 infections in animals in the studies outlined above were based on RT-PCR or virus isolation [Barrs et al., 2020; Decaro et al., 2020; Hamers et al., 2021; Ruis-Arrondo et al., 2020 & Sailleau et al., 2020).
The use of sero-detection of the anti-SARS CoV-2 antibodies has also been deployed in a number of countries with the aim of providing evidence of exposure of cats and dogs to SARS CoV-2. Independent studies in Italy have also shown evidence of exposure to SARS-CoV-2 in cats and dogs from households (Patterson et al (2020)), while in France, Frits et al (2020) showed a high prevalence of SARS-CoV-2 antibodies in pets from COVID-19 positive households (Fritzs et al., 2020). In Germany, Croatia and China the presence of anti-SARS-CoV-2 antibodies have also been shown in domestic cats and other pet populations. Collectively, these studies have demonstrated that serosurveys can provide reliable evidence of animal infections (Michelitsch et al., 2020; Stevanovic et al., 2020; Zhang et al., 2020).
A close examination of these studies reveal that most of the animals in which SARS-CoV-2 were detected were either companion or domesticated animals. This evidence has been interpreted to suggest that such domestic and companion animals could reliably predict human to animal transmissions especially post the pandemic outbreak. Additional data in support of this conclusion has also recently become available. For example, cases of experimentally induced infections have recently been documented in cats (Halfmann et al., 2020; Bosco-Lauth et al., 2020) and dogs have also been shown to be susceptible to SARS-CoV-2.
As for the epidemiological significance of these infections, cats have been shown to shed off the virus and able to transmit the virus to other cats [Shi et al., 2020; Bosco Lauth et al 2020) and cases of possible natural infections and transmissions have been detected in farmed minks that have been in contact with cats and dogs (Oude Munnink et al., 2020; van Aart et al., 2020). This data therefore suggest the possibility of human to animal transmission and vice versa. While in the studies especially in cats and dogs there were no clinical symptoms, the studies in farmed Minks whose transmissions were from infected human contact respiratory and gastrointestinal signs, and also sudden death after infection (Molenaar et al., 2020). However there were cases of nondomestic felids at the Bronx Zoo and pet cats in New York and Europe, which showed respiratory disease and/or conjunctivitis.
Although this data by itself already suggests a complex persistent zoonosis, it can be further complicated by the presence of wild animals that interface with domestic animals and humans as is the case in most parts of Africa. In other parts of the world with a domesticated animal- wild animal interface, new evidence of infection of some of these animals has recently been documented. These include: Croatia where fifteen out of 533 (2.8%) positive ELISA results has been detected in wild boars (3.9%), red foxes (2.9%) and jackals (4.6%) (Jemeršić, et al., 2021). Given these findings, it’s only a matter of time before the virus start spreading in the wild. These facts together with the evidences that a certain wild animals like the lion are susceptible to SARS CoV-2 (Koeppel et al., 2022) and develop pneumonia, could mean maintenance of the virus in the wild, with potentially negative consequences on wild populations and biodiversity. These therefore underscore the importance of extending surveillance to animals in the wild in future..
Herein, in pursuit of the broad objective of SARS-CoV-2 surveillance in domestic animals in Africa, we have developed a robust ELISA diagnostic assay based on a crude viral lysate and used it to detect antibodies to SARS-CoV-2 in cats, dogs and camels in Kenya. Our specific goal was to develop a robust ELISA diagnostics assay for SARS-CoV-2 in order to understand the seroprevalence of SARS-CoV-2 in domestic animals.