Ticks are blood-feeding ecto-parasites that have a cosmopolitan distribution in tropical and subtropical regions of the world. Ticks cause economic losses in the form of reduced blood, meat and dairy products, as well as pathogen transmission. Different acaricides such as organochlorines, organophosphates, formamidines (e.g. amitraz), synthetic pyrethroids, macrocyclic lactones, fipronil, and fluazuron are currently used sequentially or simultaneously to control tick infestations. Most acaricide treatments now face increasingly high chances of failure, due to the resistance selection in different tick populations against these drugs. Acaricide resistance in ticks can be developed in different ways, including amino acid substitutions that result in morphological changes in the acaricide target, metabolic detoxification, and reduced acaricide entry through the outer layer of the tick body. The current literature brings a plethora of information regarding the use of different acaricides for tick control, resistance selection, analysis of mutations in target sites, and resistance mitigation. Alternatives such as synergistic use of different acaricides, plant-derived phytochemicals, fungi as biological control agents, and anti-tick vaccines have been recommended to avoid and mitigate acaricide resistance. The purpose of this review was to summarize and discuss different acaricides applied for tick control, their mechanisms of action and resistance selection, genetic polymorphisms in their target molecules, as well as the approaches used for diagnosis and mitigation of acaricide resistance, specifically in Rhipicephalus microplus ticks.
Tick sialome is comprised of a rich cocktail of bioactive molecules that function as a tool to disarm host immunity, assist blood-feeding, and play a vibrant role in pathogen transmission. The adaptation of the tick’s blood-feeding behavior has lead to the evolution of bioactive molecules in its saliva to assist them to overwhelm hosts’ defense mechanisms. During a blood meal, a tick secretes different salivary molecules including vasodilators, platelet aggregation inhibitors, anticoagulants, anti-inflammatory proteins, and inhibitors of complement activation; the salivary repertoire changes to meet various needs such as tick attachment, feeding, and modulation or impairment of the local dynamic and vigorous host responses. For instance, the tick’s salivary immunomodulatory and cement proteins facilitate the tick’s attachment to the host to enhance prolonged blood-feeding and to modulate the host’s innate and adaptive immune responses. Recent advances implemented in the field of “omics” have substantially assisted our understanding of host immune modulation and immune inhibition against the molecular dynamics of tick salivary molecules in a crosstalk between the tick–host interface. A deep understanding of the tick salivary molecules, their substantial roles in multifactorial immunological cascades, variations in secretion, and host immune responses against these molecules is necessary to control these parasites. In this article, we reviewed updated knowledge about the molecular mechanisms underlying host responses to diverse elements in tick saliva throughout tick invasion, as well as host defense strategies. In conclusion, understanding the mechanisms involved in the complex interactions between the tick salivary components and host responses is essential to decipher the host defense mechanisms against the tick evasion strategies at tick-host interface which is promising in the development of effective anti-tick vaccines and drug therapeutics.
Theileria annulata is a tick-associated parasite that causes tropical theileriosis in livestock and is responsible for huge economic losses. Studies have been neglected on the effect of Theileria spp. on cattle in Khyber Pakhtunkhwa (KP), Pakistan. The present study was designed to determine the genetic diversity and assess the risk factors associated with Theileria infection in selected districts of KP. Information on the risk factors related to the Theileria infection was collected through a questionnaire. Blood samples were collected from symptomatic cattle from January 2019 to February 2020, identified morphologically through microscopic examination, and processed for molecular characterization using the 18S rRNA gene as a genetic marker. Of the 555 cattle examined (136, 24.5%) and (294, 53%) were found positive for Theileria spp. by microscopic examination and a PCR test, respectively. Based on the PCR test, the highest prevalence of infection was found in district Upper Dir (46/75, 61.3%), followed by Lower Dir (54/90, 60%); Malakand (51/88, 57.9%); Peshawar (40/80, 50%); and Charsadda (52/112, 46.4%), with the lowest in Bajaur (51/110, 46.34%). A BLAST analysis of the 18S rDNA sequences showed 99.5% identity with T. annulata. In a phylogenetic tree, the 18S rDNA sequence of T. annulata clustered with sequences from Pakistan, China, and Italy. A significant association was observed between the prevalence of infection and different host characteristics. The highest infection was found in adult cattle (216/360, 60%); females (218/377, 57.8%); and Holstein Friesian (120/180, 66.6%). Theileria infection was significantly associated with management practices. Higher infection rates were observed in free-grazing cattle (190/412, 42.2%); those kept in unhygienic conditions (246/405, 60.7%); cattle in combined farming systems (165/255, 64.8%); and those in congested stall systems (150/218, 68.8%). Seasonal patterns were found to be significantly associated with infection, and a higher infection rate was observed in summer (215/350, 61.4%) than in winter (79/205, 38.5%). Identified risk factors should be considered in designing practical control approaches to reduce the burden of Theileria infection. Large scale studies are required to explore the diversity of Theileria species in KP, Pakistan.
Background: Camel production in Saudi Arabia is severely affected by various diseases and by inadequate veterinary services. Ticks and tick-borne pathogens (TBPs ) affect the health and wellbeing of camels consequently diminishing their productivity and performances. In addition, camels may act as hosts for TBPs (e.g. Anaplasma phagocytophilum ) causing diseases in humans. The current study aimed to determine the prevalence of ixodid ticks and molecularly investigate the associated pathogens in camels from Saudi Arabia. Methods: Blood and tick samples were collected from camels ( n = 170) in Riyad Province of Saudi Arabia. Ticks were morphologically identified, and blood of camels were molecularly screened for apicomplexan (i.e. Babesia spp . , Theileria spp., Hepatozoon spp.) and rickettsial parasites (i.e. Ehrlichia spp. and Anaplasma spp.). Results: Of the 170 camels examined, 116 (68.2%; 95% CI: 60.9–75.1%) were infested by ticks with a mean intensity of 2.53 (95% CI: 2.4–2.6). In total of 296 ticks collected, Hyalomma dromedarii was the most prevalent (76.4%), followed by Hyalomma impeltatum (23.3%) and Hyalomma excavatum (0.3%). Of the tested animals, 13 (7.6%; 95% CI: 4.3–12.8%) scored positive to at least one TBP, with Anaplasma platys (5.3%; 95% CI: 2.7–9.9%) being the most prevalent species, followed by Anaplasma phagocytophilum , Anaplasma sp., Ehrlichia canis and Hepatozoon canis (0.6% each; 95% CI: 0.04–3.4%). None of the camels were found to be co-infected with more than one pathogen. All samples tested negative for Babesia spp. and Theileria spp. Conclusions: The present study reveals the occurrence of different tick species and tick-borne pathogens in camels from Saudi Arabia. Importantly, these camels may carry A. phagocytophilum and A. platys , representing a potential risk to humans.
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