Systematic, active surveillance for Middle East respiratory syndrome coronavirus in camels in Egypt

Abstract

Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe human infections and dromedary camels are considered an intermediary host. The dynamics of natural infection in camels are not well understood. Through systematic surveillance in Egypt, nasal, rectal, milk, urine and serum samples were collected from camels between June 2014 and February 2016. Locations included quarantines, markets, abattoirs, free-roaming herds and farmed breeding herds. The overall seroprevalence was 71% and RNA detection rate was 15%. Imported camels had higher seroprevalence (90% vs 61%) and higher RT-PCR detection rates (21% vs 12%) than locally raised camels. Juveniles had lower seroprevalence than adults (37% vs 82%) but similar RT-PCR detection rates (16% vs 15%). An outbreak in a breeding herd, showed that antibodies rapidly wane, that camels become re-infected, and that outbreaks in a herd are sustained for an extended time. Maternal antibodies titers were very low in calves regardless of the antibody titers of the mothers. Our results support the hypothesis that camels are a reservoir for MERS-CoV and that camel trade is an important route of introducing the virus into importing countries. Findings related to waning antibodies and re-infection have implications for camel vaccine development, disease management and zoonotic threat.

Figure 1

Map of sampling locations. Quarantines were located near the border with Sudan, abattoirs were in Cairo and the Nile Delta region, free herds and farms were in Northern Egypt.

Figure 2

Serological and viral RNA detection distribution of MERS-CoV in camels in Egypt over time. (A) Distribution of antibody titers by month. The y axis shows the percentage of seropositive samples (neutralizing antibody titer ≥1:20). (B) Detection of viral nucleic acids by month. The y axis shows the percentage of nasal swabs with confirmed MERS-CoV RNA by RT-PCR. All samples were included in the analysis. Supporting data are provided in Supplementary Table S2. Middle East respiratory syndrome coronavirus, MERS-CoV; polymerase chain reaction with reverse transcription, RT-PCR.

Figure 3

Phylogenetic tree of the partial Spike protein gene (around 600 bp) of MERS-CoV. Tree was generated using MEGA6 with bootstrap method and Kimura 2-parameter model. MERS-CoV/Camel/Egypt/NRCE-HKU205/2013 (KJ477102) was used as a root for the tree. Sequences obtained in this study are shown in red, other camel sequences are shown in blue. Middle East respiratory syndrome coronavirus, MERS-CoV.

Figure 4

(A) Comparison of seroprevalence between local and imported camels by age and sex. Numbers in the circles indicate the percentage of seropositive samples (neutralizing antibody titer ≥1:20). Arrows indicate categories compared with each other. Statistically significant differences (P-value <0.05) are denoted by *. NS denotes not statistically significant. (B) Comparison of detection of viral RNA between local and imported camels by age and sex. Numbers in the circles indicate the percentage of nasal swabs with confirmed MERS-CoV RNA by RT-PCR. Arrows indicate categories compared with each other. Statistically significant differences (P-value <0.05) are denoted by *. NS denotes not statistically significant. Middle East respiratory syndrome coronavirus, MERS-CoV; polymerase chain reaction with reverse transcription, RT-PCR.

Figure 5

Detection of viral RNA in imported (A) and local (B) camels over the surveillance period. Y axes show the percentage of nasal swabs with confirmed MERS-CoV RNA by RT-PCR. Supporting data are provided in Supplementary Table S3. Middle East respiratory syndrome coronavirus, MERS-CoV; polymerase chain reaction with reverse transcription, RT-PCR.

Figure 6

Epicurve of MERS-CoV outbreak in a local herd and the associated antibody geometric mean titers. Bars indicate the percentage of nasal swabs with confirmed MERS-CoV RNA by RT-PCR. Line indicates the geometric mean of antibody titers. Supporting data are provided in Supplementary Table S4. Middle East respiratory syndrome coronavirus, MERS-CoV; polymerase chain reaction with reverse transcription, RT-PCR.