Bactrian Camel – Credit Wikipedia
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Whenever a new infectious disease threat emerges - particularly those with zoonotic potential - one of the first things we look for is the host range of the pathogen. Whether it is avian flu, Ebola, or a vector-borne disease like Zika, it is vital to understand its host range, diversity, and ecology.
Generally speaking, the greater the host range, the greater the risk to public health.Roughly a year after the first human infection with MERS-CoV was identified in Saudi Arabia, dromedary camels were identified as major host species for the MERS coronavirus (see 2013's The Lancet Camels Found With Antibodies To MERS-CoV-Like Virus).
Bats are still believed to be the primary host reservoir for MERS, SARS, and an array of other novel pathogens (see Curr. Opinion Virology: Viruses In Bats & Potential Spillover To Animals And Humans), but the hunt continues for other susceptible species where these viruses may reside.Complicating this search, the MERS virus doesn't appear to leave long lasting fingerprints - in the form of detectable antibodies - once the host clears the infection (see EID Journal: Antibody Response & Disease Severity In HCW MERS Survivors).
Similar waning antibody detection has been reported in camels, which means seroprevalence studies may not provide an accurate picture of how many people - or other species - have been infected with this coronavirus in the past.In an attempt to get past this testing barrier, we've seen a number of studies that have tried to experimentally infect various species in order to identify other potential hosts.
In 2016, in Study: Experimental Infection Of Goats, Sheep & Horses With MERS-CoV, we looked at a study that reassuringly found that:
Minimal or no virus shedding was detected in all of the animals. During the four weeks following inoculation, neutralizing antibodies were detected in the young goats, but not in sheep or horses.Four months later, in December of 2016, in EID Journal: Livestock Susceptibility to Infection with MERS-CoV, researchers experimentally inoculated llamas, pigs, sheep, and horses with the MERS virus, and found that pigs & llamas both shed the virus from the nose, and seroconverted.
Given the susceptibility of pigs to other coronaviruses (see mBio: PEDV - Porcine Epidemic Diarrhea Virus - An Emerging Coronavirus and Swine Enteric Coronavirus Diseases), this understandably raised concerns.A 2017 study (see EID Journal: Domestic Pig Unlikely Reservoir for MERS-CoV) confirmed that while pigs can be experimentally infected with the MERS virus, they did not develop clinical disease and only shed small quantities of the virus, making them unlikely to spread the disease.
Although Bactrian camels, which are commonly found in Mongolia, Central Asia, Pakistan, and Iran belong to the same family as Dromedaries (Camelidae), a 2015 Research letter in the EID Journal found an Absence of MERS-Coronavirus in Bactrian Camels, Southern Mongolia, November 2014.As Dromedaries and Bactrian camels share some limited geographic regions, the potential of MERS-CoV spreading to Bactrian camels - and thereby extending its threat to other human populations - is obviously a concern.
All of which brings us to a new study, published last week in Emerging Microbes & Infections, where researchers from NIAID and the Department of Biomedical Sciences at Colorado State University, inoculated two Bactrian camels and monitored them for nasal shedding and seroconversion.This is an open access article, and I've only posted a few excerpts. Follow the link to either read (or listen to), the full article.
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Original Articles
Bactrian camels shed large quantities of Middle East respiratory syndrome coronavirus (MERS-CoV) after experimental infection
Danielle R. Adney, Michael Letko, Izabela K. Ragan, Dana Scott, Neeltje van Doremalen, Richard A. Bowen & Vincent J. Munster
https://doi.org/10.1080/22221751.2019.1618687
Pages 717-723 | Received 05 Apr 2019, Accepted 09 May 2019, Published online: 23 May 2019
ABSTRACT
In 2012, Middle East respiratory syndrome coronavirus (MERS-CoV) emerged. To date, more than 2300 cases have been reported, with an approximate case fatality rate of 35%. Epidemiological investigations identified dromedary camels as the source of MERS-CoV zoonotic transmission and evidence of MERS-CoV circulation has been observed throughout the original range of distribution.
Other new-world camelids, alpacas and llamas, are also susceptible to MERS-CoV infection. Currently, it is unknown whether Bactrian camels are susceptible to infection. The distribution of Bactrian camels overlaps partly with that of the dromedary camel in west and central Asia.
The receptor for MERS-CoV, DPP4, of the Bactrian camel was 98.3% identical to the dromedary camel DPP4, and 100% identical for the 14 residues which interact with the MERS-CoV spike receptor. Upon intranasal inoculation with 107 plaque-forming units of MERS-CoV, animals developed a transient, primarily upper respiratory tract infection.
Clinical signs of the MERS-CoV infection were benign, but shedding of large quantities of MERS-CoV from the URT was observed. These data are similar to infections reported with dromedary camel infections and indicate that Bactrians are susceptible to MERS-CoV and given their overlapping range are at risk of introduction and establishment of MERS-CoV within the Bactrian camel populations.(SNIP)
Discussion(Continue . . . )
Despite the current lack of field evidence of MERS-CoV infection in Bactrian camels, this study demonstrates that Bactrian camels can be readily infected and shed large quantities of virus in nasal secretions. If MERS-CoV were to be introduced into populations of Bactrian camels, we would expect that a potential endemic and sustained pattern of infection may result and they could act as a reservoir, similar to dromedaries, potentially exposing associated human communities to infection.
