Ticks; a reservoir for virus emergence at the human-livestock interface in Uganda
Authors: Atim Stella A. , Ashraf Shirin , Niebel Marc , Ssekagiri Alfred , Hardy Maryam N. , Shepherd James G. , Tong Lily , Ademun Anna R , Vudriko Patrick , Erume Joseph , Odongo Steven , Muhanguzi Denis , Nguma Willy , Nakayiki Dip Teddy , Namulondo Joyce , Filipe Ana , Lutwama Julius J , Kaleebu Pontiano , Masembe Charles , Tweyongyere Robert , Thomson Emma C. 
Published: March 2023

Background

Uganda is one of the most biodiverse regions on the planet and a hotspot for virus emergence. In particular, the warm-humid lowlands favour tick population growth with the associated risk of tick-borne disease. The prevalent tick speciesRhipicephalus appendiculatus, R. evertsi evertsiandAmblyomma variegatumharbour a diverse range of viruses, from harmless to highly pathogenic. Notably, the orthonairoviruses cause human outbreaks of Crimean-Congo haemorrhagic fever (CCHF) regularly within the cattle corridor of Uganda, a region spanning from the south-west to the north-east of the country.

Methods

In the ArboViral Infection (AVI) study, the first to explore the virome of ticks in Uganda using next generation sequencing (NGS), we collected ticks from three geographically diverse areas and subjected these to target-enrichment (TE) NGS. Viral genomes were detected byde novoassembly, mapping and BLASTn.

Results

We analyzed a total of 2,754 ticks collected from 31 livestock farms in the districts of Arua, Nakaseke and Lyantonde. These were combined into 219 pools by site of collection and tick species, includingR. appendiculatus, R. evertsi evertsi,A. variegatumandHyalomma rufipes. We detected partial or near-complete viral genomes in 163 tick pools; 110 (67%) of which were from Arua, 39 (24%) from Nakaseke and 12 (7%) from Lyantonde districts. 2 pools (2%) were from Arua/Lyantonde. These included 22 species of virus, representing 15 genera and 9 families, including theNairoviridae,Retroviridae,Orthomyxoviridae,Chuviridae,Rhabdoviridae,Phenuiviridae, Parvoviridae, PoxviridaeandFlaviviridae. There were 8 viral species known to be pathogens of humans or animals and 5 highly divergent genomes detected, representing novel virus species. A high abundance of orthonairoviruses was notable, including CCHFV, Dugbe virus and a novelOrthonairovirusspecies that we have named Macira virus.

Interpretation

Ticks in Uganda are an important reservoir of diverse virus species, many of which remain uncharacterised and of unknown pathogenic potential.

Author Summary

Ticks are parasitic arachnids that may transmit a spectrum of viral diseases to humans and animals. Uganda is a hotspot for such tick-borne diseases. In this study, we sequenced ticks collected from three geographically diverse regions of Uganda using a semi-agnostic next- generation sequencing method in order to detect viruses from all known virus families. We collected and analyzed 2,754 ticks from 31 farms across the country. Within these ticks, we detected 22 species of virus from 15 genera and 9 viral families, including 8 animal or human pathogens and 5 new novel virus species. Notably, orthonairoviruses, including the highly pathogenic Crimean-Congo haemorrhagic fever virus, were highly prevalent in the ticks. The researchers suggest that ticks in Uganda serve as an important reservoir for diverse viruses, many of which have significant pathogenic potential. This information will inform public health efforts to prevent and control tick-borne diseases in Uganda and other similar regions.