Potential causes of Acaricide Resistance in Rhipicephalus and Amblyomma Ticks (Acari: Ixodidae) in Namwala District, Zambia

Acaricide resistance in ticks poses a great threat to livestock production in many parts of the world where ticks are a problem. The objectives of this study were to screen for acaricide resistance in Rhipicephalus and Amblyomma ticks using phenotypic and molecular assays, and to assess current tick control practices used by cattle farmers in the traditional sector of Namwala District. The larval packet test was used to screen for acaricide resistance in ticks covering concentrations up to twice the discriminatory dose for amitraz, diazinon and cypermethrin. Genetic mutations associated with resistance to amitraz (A22C-T8P and T65C-L22S), and organophosphates/ pyrethroids (G1120A) were screened using polymerase chain reaction and sequencing. Information on tick control practices at the household level was collected using a semi-structured questionnaire. Intermediate resistance (21-50%) to amitraz and cypermethrin was detected in both Rhipicephalus and Amblyomma ticks, with both tick genera showing susceptibility to diazinon (<10%). None of the ticks in this study had the reported acaricide resistance-conferring molecular markers that were screened for. The findings suggest that the resistance detected in the studied tick population may be due to other mechanisms that are yet to be identified. Tick control practices observed amongst the farmers, such as incorrect use of acaricide concentrations and rotations could be fuelling the development of acaricide resistance. It is critical to comprehensively unravel the factors that could be contributing to acaricide treatment failure as this would allow for application of appropriate remedial actions for effective tick control in Zambia.

Short communication: Potential causes of Acaricide Resistance in Rhipicephalus and Amblyomma Ticks (Acari: Ixodidae) in Namwala District, Zambia

Acaricide resistance in ticks poses a great threat to livestock production in many parts of the world where ticks are a problem. The objectives of this study were to screen for acaricide resistance in Rhipicephalus and Amblyomma ticks using phenotypic and molecular assays, and to assess current tick control practices used by cattle farmers in the traditional sector of Namwala District. The larval packet test was used to screen for acaricide resistance in ticks covering concentrations up to twice the discriminatory dose for amitraz, diazinon and cypermethrin. Genetic mutations associated with resistance to amitraz (A22C-T8P and T65C-L22S), and organophosphates/ pyrethroids (G1120A) were screened using polymerase chain reaction and sequencing. Information on tick control practices at the household level was collected using a semi-structured questionnaire. Intermediate resistance (21-50%) to amitraz and cypermethrin was detected in both Rhipicephalus and Amblyomma ticks, with both tick genera showing susceptibility to diazinon (<10%). None of the ticks in this study had the reported acaricide resistance-conferring molecular markers that were screened for. The findings suggest that the resistance detected in the studied tick population may be due to other mechanisms that are yet to be identified. Tick control practices observed amongst the farmers, such as incorrect use of acaricide concentrations and rotations could be fuelling the development of acaricide resistance. It is critical to comprehensively unravel the factors that could be contributing to acaricide treatment failure as this would allow for application of appropriate remedial actions for effective tick control in Zambia.

Scoping review of distribution models for selected Amblyomma ticks and rickettsial group pathogens

The rising prevalence of tick-borne diseases in humans in recent decades has called attention to the need for more information on geographic risk for public health planning. Species distribution models (SDMs) are an increasingly utilized method of constructing potential geographic ranges. There are many knowledge gaps in our understanding of risk of exposure to tick-borne pathogens, particularly for those in the rickettsial group. Here, we conducted a systematic scoping review of the SDM literature for rickettsial pathogens and tick vectors in the genus Amblyomma. Of the 174 reviewed articles, only 24 studies used SDMs to estimate the potential extent of vector and/or pathogen ranges. The majority of studies (79%) estimated only tick distributions using vector presence as a proxy for pathogen exposure. Studies were conducted at different scales and across multiple continents. Few studies undertook original data collection, and SDMs were mostly built with presence-only datasets from public database or surveillance sources. The reliance on existing data sources, using ticks as a proxy for disease risk, may simply reflect a lag in new data acquisition and a thorough understanding of the tick-pathogen ecology involved.

Amblyomma ticks and future climates.

This expert opinion discusses the evidence of how the climate can influence the distribution of ticks of the Amblyomma genus, as well as the prevalence of tick-borne diseases, in climate change scenarios.

Molecular detection of Rickettsia africae in Amblyomma ticks collected in cattle from Southern and Central Mozambique

Introduction: Rickettsia are Gram-negative and obligate intracellular bacteria, which cause typhus and spotted fever-like diseases in humans. In Africa, Rickettsia africae of the Spotted Fever Group Rickettsia (SFGR) is the etiologic agent of the African Tick-Bite Fever. The disease is transmitted by ticks of the genus Amblyomma, which serve as vectors and reservoirs of Rickettsia. In this study, we aimed to detect Rickettsia species in ticks collected from cattle in south and central Mozambique. Methodology: DNA from 412 adult ticks and 22 pools of larvae were extracted and tested for the presence of Rickettsia genes gltA, ompA and ompB by PCR, followed by sequencing and phylogenetic analysis. Results: Our results showed that in adult ticks, 79.5% (n = 330), 66% (n = 274) and 67% (n = 275) samples were positive for gltA, ompA and ompB genes, respectively. Among the 22 pools of larvae analysed, 77.2% (n = 17) were positive for the three genes tested. The infection rates ranged from 43% to 100% for Rickettsia by gltA in all locations studied, with maximum values of 100% observed in the districts of Maputo province namely Changalane, Boane and Matutuine district. The phylogenetic analysis of amplified sequences revealed that samples under study grouped with R. africae for the 3 genes. Conclusion: The study showed that Spotted Fever Group Rickettsia represented by R. africae widely circulate in Amblyomma ticks collected in south and central regions of Mozambique.

Systematic review of distribution models for Amblyomma ticks and Rickettsial group pathogens

The rising prevalence of tick-borne diseases in humans in recent decades has called attention to the need for more information on geographic risk for public health planning. Species distribution models (SDMs) are an increasingly utilized method of constructing potential geographic ranges.There are many knowledge gaps in our understanding of risk of exposure to tick-borne pathogens, particularly for those in the rickettsial group. Here, we conducted a systematic review of the SDM literature for rickettsial pathogens and tick vectors in the genus Amblyomma. Of the 174 reviewed papers, only 24 studies used SDMs to estimate the potential extent of vector and/or pathogen ranges. The majority of studies (79%) estimated only tick distributions using vector presence as a proxy for pathogen exposure. Studies were conducted at different scales and across multiple continents. Few studies undertook original data collection, and SDMs were mostly built with presence-only datasets from public database or surveillance sources. While we identify agap in knowledge, this may simply reflect a lag in new data acquisition and a thorough understanding of the tick-pathogen ecology involved.

Molecular detection of rickettsial agents of hard ticks (Acari: Ixodidae) collected from wild birds of Panama

Ticks (Acari: Ixodidae) collected from wild birds in Panama were tested for the presence of tick-borne pathogens as Rickettsia, Anaplasma, Ehrlichia, Bartonella, Borrelia, Hepatozoon sp., and Babesia. Overall 124 ticks were found in 57 birds belonging to 28 species: Amblyomma longirostre (32 larvae, 1 nymph), Amblyomma nodosum (30 nymphs), Amblyomma geayi (15 larvae, 1 nymph), Amblyomma varium (5 larvae, 2 nymphs), Amblyomma naponense (2 larvae), Amblyomma ovale (2 larvae), and Amblyomma calcaratum (1 larva). DNA of Rickettsia amblyommatis was detected in 65% of A. longirostre, 69% of A. geayi and 14% of A. varium. Moreover, results from two larvae of A. longirostre showed DNA of unidentified Rickettsia sp. No DNA of Borrelia, Bartonella, Anaplasmataceae neither Babesia nor Hepatozoon was detected. These results expand knowledge about the host for immature Amblyomma ticks in Panama and show the first data of Rickettsia in ticks collected from birds in this country.