Abstract
Anaplasmosis, caused by infection with bacteria of the genus Anaplasma, is an important veterinary and zoonotic disease. Transmission by ticks has been characterized but little is known about non-tick vectors of livestock anaplasmosis. This study investigated the presence of Anaplasma spp. in camels in northern Kenya and whether the hematophagous camel ked, Hippobosca camelina, acts as a vector. Camels (n = 976) and > 10,000 keds were sampled over a three-year study period and the presence of Anaplasma species was determined by PCR-based assays targeting the Anaplasmataceae 16S rRNA gene. Camels were infected by a single species of Anaplasma, 'Candidatus Anaplasma camelii', with infection rates ranging from 63-78% during the dry (September 2017), wet (June-July 2018), and late wet seasons (July-August 2019). 10-29% of camel keds harbored 'Ca. Anaplasma camelii' acquired from infected camels during blood feeding. We determined that Anaplasma-positive camel keds could transmit 'Ca. Anaplasma camelii' to mice and rabbits via blood-feeding. We show competence in pathogen transmission and subsequent infection in mice and rabbits by microscopic observation in blood smears and by PCR. Transmission of 'Ca. Anaplasma camelii' to mice (8-47%) and rabbits (25%) occurred readily after ked bites. Hence, we demonstrate, for the first time, the potential of H. camelina as a vector of anaplasmosis. This key finding provides the rationale for establishing ked control programmes for improvement of livestock and human health.
Highlights
Little is known about the role of common camel-specific biting keds in pathogen transmission
We demonstrated using amplicon sequencing that camel keds can transmit
Anaplasma species are obligate rickettsial pathogens that proliferate inside red blood cells and cause anaplasmosis in domestic and wild animals
Summary
Anaplasma species are obligate rickettsial pathogens that proliferate inside red blood cells and cause anaplasmosis in domestic and wild animals. Clinical signs of anaplasmosis during acute infection include anaemia, pyrexia, reduced milk yield, loss of body condition, abortion, and death [3,4,5]. Anaplasma is transmitted by different species of hard ticks [6] as well as mechanically via contaminated mouthparts of Stomoxys calcitrans and Tabanidae, among other biting flies, albeit with reduced efficiency [7,8]. Pathogen transmission can occur via needles and other veterinary instruments contaminated with fresh infected blood [9]. Mechanical transmission of Anaplasma pathogens is thought to be possible only at high parasitaemia [7]
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