Molecular Detection of Anaplasma Phagocytophilum in Small Mammals and Infesting Ticks in Laikipia County, Kenya

Abstract

Anaplasmosis refers to a series of diseases affecting a variety of animals, as a result of infection by bacteria from the genus Anaplasma. Bacteria in this genus are characterised as gram-negative, obligate intracellular organisms capable of infecting various animals. Anaplasma species found within the genus include Anaplasma ovis, Anaplasma marginale, Anaplasma mesaeterum, Anaplasma platys and Anaplasma phagocytophilum. Anaplasma phagocytophilum is one of the significant zoonotic species causing Human Granulocytic Anaplasmosis a disease characterized mainly by febrile illness syndrome. Despite the wide distribution of A. phagocytophilum, only a few epidemiological reports have been documented in the sub-Saharan African countries such as Kenya. Therefore, this study aimed at identification and determination of A. phagocytophilum circulating in Small Mammals and associated ticks in Laikipia County. To accomplish the study objectives a sum of 385 blood and 84 tick archival samples from rodents (155 females and 230 males) were analysed for A. phagocytophilum. Blood sampled from Small Mammals were analysed by PCR-HRM analysis using primers that amplified the 16S ribosomal RNA. Infesting tick samples were also analysed by PCR-HRM analysis using primers derived from 16S rRNA. The results showed 19 out of 385 small mammal samples tested positive demonstrating a prevalence of 4.9%. Results from tick’s sample analysis also revealed 3 ticks of genus Haemaphysalis leachi (3/84) reacted positive corresponding to a prevalence of 3.6%. This study's prevalence varied between species of small Mammals examined (P = 0.021), with Arvicanthis niloticus (The African grass rat) exhibiting the highest prevalence of about 18.8%. Sequencing of the haplotypes from the study confirmed of Anaplasma phagocytophilum in the analysed positive samples. In GenBank BLAST analysis, haplotypes from this study had 98% to 100% identity similarity to a previously reported isolate 9B13 from Alces alces (KC800985).

Phylogenetic analysis of the haplotype obtained revealed ancestral relationship with strains from ticks (Haemaphysalis longicornis), Canis familiaris, A. alces, and A. agrarius that have been recorded in European Countries, China, and African Countries. Analysis was performed to determine relationship with the known human pathogenic A. phagocytophilum (variant HA) with non-pathogenic (variant 1). The analysis showed the published human pathogenic A. phagocytophilum (variant HA) with non-pathogenic (variant 1) variants formed a unique cluster distinct from haplotypes found in this investigation. Sequences reported in this investigation were published in GenBank with accession numbers OQ308965-OQ308976. This study indicates that, small mammals and their associated tick harbours A. phagocytophilum. Ability of H. leachi to act as a vector in the transmission of A. phagocytophilum transmission warrants additional investigation to assess the potential public health threat.