Clinical and molecular epidemiology of Crimean-Congo hemorrhagic fever in Oman

Abstract

Background: Crimean-Congo hemorrhagic fever (CCHF) is a serious disease with a high fatality rate reported in many countries. The first case of CCHF in Oman was detected in 1995 and serosurveys have suggested widespread infection of humans and livestock throughout the country.

Methodology: Cases of CCHF reported to the Ministry of Health (MoH) of Oman between 1995 and 2017 were retrospectively reviewed. Diagnosis was confirmed by serology and/or molecular tests in Oman. Stored RNA from recent cases was studied by sequencing the complete open reading frame (ORF) of the viral S segment at Public Health England, enabling phylogenetic comparisons to be made with other S segments of strains obtained from the region.

Findings: Of 88 cases of CCHF, 4 were sporadic in 1995 and 1996, then none were detected until 2011. From 2011-2017, incidence has steadily increased and 19 (23.8%) of 80 cases clustered around Eid Al Adha. The median (range) age was 33 (15-68) years and 79 (90%) were male. The major risk for infection was contact with animals and/or butchering in 73/88 (83%) and only one case was related to tick bites alone. Severe cases were over-represented: 64 (72.7%) had a platelet count < 50 x 109/L and 32 (36.4%) died. There was no intrafamilial spread or healthcare-associated infection. The viral S segments from 11 patients presenting in 2013 and 2014 were all grouped in Asia 1 (IV) lineage.

Conclusions: CCHF is well-established throughout Oman, with a single strain of virus present for at least 20 years. Most patients are men involved in animal husbandry and butchery. The high mortality suggests that there is substantial under-diagnosis of milder cases. Preventive measures have been introduced to reduce risks of transmission to animal handlers and butchers and to maintain safety in healthcare settings.

Fig 1. Yearly distribution of CCHF cases and deaths reported in Oman: 1995–2017.

Fig 2. Map of Oman with number of CCHF cases, superimposed on results of previous animal serosurveys for CCHFV antibodies and tick surveys for CCHFV (24–25).

The map was constructed using QGIS software (QGIS Development Team (2018). QGIS Geographic Information System. Open Source Geospatial Foundation Project. http://qgis.osgeo.org) using data from the directorate general for planning, ministry of health, Oman.

Fig 3. Weekly distribution of CCHF cases in Oman showing clustering after Eid Al Adha: 2013–2017 (n = 80).

Eid Al Adha occurs 10 days earlier in each successive year, indicated by the pale vertical columns between weeks 35 and 43. The risk period is defined as approximately 10 days after the Eid Al Adha festival.

Fig 4. Phylogenetic tree showing Omani sequences clustering in Asia 1 lineage, with other sequences from the GCC region previously deposited in Genbank.