Home Medizin Studie zeigt saisonale MERS-CoV-Höhepunkte bei kenianischen Kamelen und eine mögliche Übertragung auf den Menschen

Studie zeigt saisonale MERS-CoV-Höhepunkte bei kenianischen Kamelen und eine mögliche Übertragung auf den Menschen

von NFI Redaktion

In a recent study published in the CDC journal Newly emerging infectious diseases, researchers estimated the frequency and potential transmission of the Middle East Respiratory Syndrome Coronavirus (MERS-CoV) to humans from dromedary camels in northern Kenya. They found that the incidence of MERS-CoV in these animals was biphasic and peaked in October 2022 and February 2023. Furthermore, it was observed that slaughterhouse workers in contact with the dromedaries showed serological signs of MERS-CoV exposure.

Study reveals seasonal MERS-CoV peaks in Kenyan camels and potential human transmission

Image Source: Hamady / Shutterstock

Background

MERS-CoV is prevalent in dromedaries on the Arabian Peninsula and in Africa, with a seroprevalence of >75%. Zoonotic transmission to humans, especially on the Arabian Peninsula, has resulted in >2,400 cases and >800 deaths. Despite camel husbandry being a significant activity in Kenya, only three cases of MERS-CoV in humans exposed to camels were identified in 2019, indicating regional epidemiological differences.

MERS-CoV outbreaks in bred dromedaries have been associated with the annual camel birth, with calves testing positive for MERS-CoV ribonucleic acid (RNA) after losing maternal antibodies. Nomadic camels in Africa, with fluctuating population density due to seasonality and food availability, have shown correlations between high population density and MERS-CoV seropositivity in Kenya, indicating gaps in our understanding of MERS-CoV circulation.

Limited infrastructure hampers field studies on nomadic camels, but the regular transportation of these animals to slaughterhouses allows for continuous testing. Utilizing this setup, the researchers conducted a year-long study in a slaughterhouse center in northern Kenya to estimate the MERS-CoV incidence in dromedaries and its potential transmission to workers at the site.

About the Study

The study was conducted in a slaughterhouse center in Isiolo, northern Kenya, with sampling conducted from September 2022 to September 2023. Samples were collected from 10-15 dromedaries at a frequency of 4-5 days per week. The camels (n = 2,711) were from various administrative districts (n = 12), mainly from Laisamis and Burat.

MERS-CoV RNA detection was carried out using quantitative reverse transcription polymerase chain reaction (qRT-PCR), with confirmation done through open reading frame (ORF) 1ab qRT-PCR or sequencing. Additionally, a phylogenetic analysis was performed. Random camel serum samples (n = 369) were tested to determine MERS-CoV immunoglobulin G (IgG) levels using an enzyme-linked immunosorbent assay (ELISA), with values for optical density ratio (ODR) determined. Statistical analyses were conducted to examine the relationships between MERS-CoV IgG levels, RNA positivity, seasonality, camel gender, and age.

Seroepidemiological investigations were conducted on slaughterhouse workers in contact with dromedaries. MERS-CoV S1-IgG reactivity was evaluated using ELISA. Possible cross-reactivity with SARS-CoV-2 antibodies was ruled out by comparing ELISA ODRs between MERS-CoV S1 and SARS-CoV-2 S1 assays. Neutralization tests (NT) were conducted using green fluorescent protein (GFP)-encoding pseudoparticles of the vesicular stomatitis virus (VSVpp) carrying MERS-CoV S protein from two groups. Tests were carried out on seven serum samples at a dilution of 1:20. A plaque-reduction neutralization test (PRNT) based on MERS-CoV EMC/2012 was conducted.

Results and Discussion

MERS-CoV RNA was detected in 1.3% of the camels. It was found that the cumulative RNA positivity rate in September-October 2022 (5.0%) was higher than in January-March 2023 (2.3%). The incidence showed biphasic peaks in October 2022 and February 2023. Phylogenetic analysis revealed high similarity (>99.93% nucleotide identity) with MERS-CoV strains from Akaki, Ethiopia, in 2019, grouping within the C2.2 group, which originally included identified strains in Kenya in 2018, indicating three presumed MERS-CoV outbreaks in Kenyan camels.

The MERS-CoV IgG levels had an average ODR of 2.14 with a seroprevalence of 80.76%. IgG levels were lowest in June and highest in March. A negative correlation was found between MERS-CoV IgG levels and RNA positivity. RNA positivity was found to be negatively associated with seasonality. Male camels showed a higher likelihood of being RNA positive and a lower likelihood of seropositive compared to female camels. Older animals (>3 years) had a higher (but statistically non-significant) seropositivity rate (86%) compared to animals ≤3 years (72%).

MERS-CoV S1-IgG reactivity was found in 14.6% of Isiolo slaughterhouse workers. The absence of MERS-CoV S1-IgG reactivity was observed in a control cohort (n = 12) without camel exposure despite high SARS-CoV-2 S1-IgG levels (92%). Remarkably, one serum sample showed a 50-90% reduction in plaque-forming units by VSVpp-NT. Additionally, PRNT results confirmed a MERS-CoV seroconversion for the sample. None of the MERS-CoV ELISA-negative samples showed neutralization capacity in VSVpp-NT and PRNT assays.

Conclusion

In conclusion, the study revealed a biphasic incidence of MERS-CoV in dromedaries, potentially influenced by increased animal interactions during transportation and seasonal factors. The evidence of human transmission in the study underscores the need for enhanced surveillance and preventive measures to mitigate the risk of zoonotic transmission. Further research is necessary to investigate the dynamics of MERS-CoV circulation and formulate strategies for potential disease control and prevention.

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