Tick-borne rickettsial diseases are considered as one of the major constraints to livestock improvement programmes as they are responsible for serious health problems resulting in reduced animal productivity and economic losses [15]. It has been documented that ticks of Rhipicephalus sp. and Haemaphysailis sp. are responsible to transmit Anaplasma marginale to a variety of vertebrate host due to elevated temperature and favorable climate, in tropical countries [16]. Our results are in line with these established facts as in present study, ticks belonging to, Rhipicephalus and Haemaphysalis were identified from the cattle under investigation during morpho-taxonomic identification (data not shown here).
Diagnosis of A. marginale is performed by both modern and conventional methods. The most common but less reliable method is the Giemsa stained blood smear screening for the detection of these bacteria within the erythrocytes [17]. However, this technique is unable to detect pre-symptomatic, and carrier animals having low parasitemia [18]. PCR is usually considered as gold standard for the detection of tick borne blood parasites and it is more sensitive and reliable than parasite detection by blood smear screening [6]. The sensitivity of PCR for detection of Anaplasma marginale (8.6% prevalence) was higher than the blood smears screening (4.3% prevalence) during present study. Ybanez et al. [19] had also documented that PCR based detection of Anaplasma marginale is more sensitive tool than through Giemsa stained blood smear screening. Several studies regarding the detection of Anaplasma marginale infection in cattle have been reported from Africa {25.4% in Tunisia [20]); 21.9% in Morocco [21], 6.1% in Sudan [22] and 3.7% in Egypt[23]},2.3% from Turkey [24] and 5.4% from Brazil [25]. There are few studies from various parts of Pakistan reporting the prevalence of Anaplasma marginale in cattle. Atif et al. [26] had reported 9% prevalence of Anaplasma marginale in Giemsa stained blood smear of cattle collected from Sargodha District in Punjab. Sajid et al. [27] had reported 4.07% (34/836) prevalence of Anaplasma marginale in cattle samples collected from Khanewal District in Punjab through blood smear screening. In a recent study, Turi et al. [28] has reported 41.6% prevalence of Anaplasma marginale in cattle blood samples collected from District Peshawar and Lakki Marwat through real time PCR technique. Similarly, Farooqi et al. [29] has reported PCR based prevalence to be 18.33% (165/900) in cattle and buffalo blood samples collected from various parts of Khyber Pukhtoon Khwa. The difference in infection rates of Anaplasma marginale may be due to differences in tick control programmes, habitat suitability for ticks, farm management, husbandry practices, wildlife reservoir hosts and/or abiotic factors as reported by others [20, 30].
The data on genetic diversity of Anaplasma marginale is very rare from Pakistan. To investigate the genetic background of Anaplasma marginale present in Pakistan, we performed phylogenetic analysis based on a 265 base pair amplicon from major surface protein–1b gene that revealed greater genetic diversity as several diverse genetic groups can be seen in phylogenetic tree based on partial sequence homology (Fig. 2). Analysis revealed that sequences obtained during present study are clustered with the previously reported sequences from United States of America (AF348137 and CP000030) indicating that these are closely related genetic variants (Fig. 1).
Prevalence of Anaplasma marginale varied with sampling season during present study and highest parasite prevalence was observed during autumn (Table 1). High parasite prevalence in autumn during present study is probably due to abundance of vector ticks that were developed during summer months. Our result is contradictory to the findings of Vohra et al. [31] and Roy et al. [32] who had reported high prevalence of Anaplasma marginale in summer season. These differences observed in the prevalence between these studies are due to different geographical locations, abundance of tick vector and breeding microenvironment of ticks (temperature and humidity)[33].
According to our result Holstein Friesian breed had highest infection rate of Anaplasma marginale as compared to cross and Sahiwal breed (Table 1). Our result is in line with result of Tay et al. [34] who had reported that Anaplasma spp. prevalence was higher in Holstien cattle as compared to local breeds. This result may be due to some kind of resistance of the local breed that is developed against rickettsial infection. Indeed, local breeds are known to be more resistant to tick-borne pathogens [3]. Longer and thicker hairs of Holstein Friesian breed may be the factor for their higher infestion of ticks as compared to other breed. It has been reported that there is a positive association of hair length and coat thickness with the number of ticks [35]. However, our result is contradictory to findings of Belkahia et al. [20] who had showed Holstein cattle were significantly less infected by Anaplasma marginale (p < 0.001) than other breeds.
Epidemiological data analysis for gender, although remained non significant, revealed that female cattle were more prone to Anaplasma marginale infection than male. This is in accordance with Kamani et al. [36] who revealed prevalence of Anaplasma infection was higher in female cattle possibly due to the fact that they were kept longer for breeding and milk production purpose, supplied insufficient feed against their high demand. The immune suppression in advanced pregnancy and or lactation in high producing study animals are the possible reasons for the higher prevalence of Anaplasma marginale in female cattle [8]. The dog associated with herd of cattle is another parameter that has showed significant association with the Anaplasma infection indicating that dogs are acting as tick carrier and bring the infection to the herd Our results are contradictory to Ashraf et al. [6] which showed higher Anaplasma marginale prevalence in buffalo herds without dog. Significantly higher prevalence of Anaplasma marginale was observed in traditionally managed farms where the animals were not regularly vaccinated against tick borne diseases and water was supplied through pools with contaminated water instead of pumps providing fresh ground water. Our results is in accordance with Swai et al. [37] and Atif et al. [38] who had reported significantly higher prevalence of Anaplasma marginale in traditionally managed farms when compared to modern ones. Poor management, lack of tick control practices and inadequate economic sustainability of poor resource smallholders may contribute to the higher prevalence of Anaplasma marginale [38].
Analysis of the complete blood count parameters indicated significant decrease in hematocrait, mean cell hemoglobin and mean corpuscular hemoglobin concentration in parasite positive cattle. These observations are in line with Gannguly et al. [39] who had reported that in severely infected cases, cattle had hemoglobin level as low as 3 g/dl and packed cell volume was decreased to 1.99 × 106/µl. This might be due to damage caused by Anaplasma marginale inside the RBC’s during their multiplication. Our result is also in accordance with Riond et al. [40] who had reported decreased mean corpuscular hemoglobin concentration and increased mean corpuscular volume in Anaplasma marginale infected as compared to uninfected cattle. They have reported that fast destruction of RBCs by phagocytosis leads to their increased demand, therefore bone marrow cells starts to release immature RBCs. The immature RBCs are bigger in size than mature RBCs having more corpuscular volume. In present study, the mean corpuscular volume was non- significantly increased in infected animals. It reflects that animal’s haemopiotic system was activated in response to erythrophagocytosis initiated by parasitic damage to erythrocytes and that leads to decrease in RBC, this may be also due to increased level of activated complement products and removal of destroyed cells by bovine reticuloendothelial system [41]. Analysis of hematological parameters indicated that white blood cells, platelet count and lymphocytes (%) were significantly decreased in Anaplasma marginale positive cattle blood samples than in blood samples where parasite was not detected (Table 3). Our result coincide with Khan et al. [42] who recorded significant decrease of WBCs in prepatent phase and non-significant decrease of WBCs in early and late stages of the disease. Our results are in agreement with the finding of Riond et al. [40] who had reported that anemic cattle showed thrombocytopenia i.e a condition in which there is a low blood platelet count. The increased platelet consumption may be attributed to an immune-mediated process or result from intravascular disseminated coagulation [43].
In conclusion, we are reporting the prevalence of Anaplasma marginale infection in three cattle breeds from Pakistan with Holstein Friesian breed being most susceptible to this infection. We have documented that PCR is more reliable and sensitive technique for Anaplasma marginale detection than blood smear screening. We are also reporting that parasite prevalence varied with the sampling season and presence of Anaplasma marginale had significant effects on the hematological profile of all cattle breeds under investigation. Data generated through this study will pave the way for the control of anaplasmosis in Pakistan. We recommend this technique to the livestock owners for prophylactic detection of Anaplasma marginale in cattle blood in order to improve their economic output.