The distribution of Babesia divergens infection within the cattle population of Northern Ireland

Surveillance and Risk Analysis for Bovine Babesiosis in England and Wales to Inform Disease Distribution

Babesia divergens is a zoonotic piroplasm that infects both cattle and humans in Europe. Disease transmission occurs through Ixodes ricinus tick bites, a species that is increasing in abundance and distribution across Europe in response to climate and land-use changes. Developments in agri-environment policy and changing consumer demands may also have unintended consequences on tick-borne disease rates. Currently, B. divergens surveillance in British cattle is limited, rendering temporal trend analysis and the detection of potential zoonotic hotspots impossible. The objective of this study was to assess syndromic surveillance as a means of determining babesiosis distribution in British cattle, and to evaluate the intrinsic disease risk factors in order to respond to disease threats posed by changing environments. Samples from 95 clinically affected cattle on 70 unique holdings were screened for Babesia spp., using established blood smear examination techniques and a B. divergens-specific PCR method, between April and December 2021. B. divergens was detected in 45/95 animals (47.4%), with PCR offering the advantage of identification at species level. Infection with Anaplasma phagocytophilum was detected in 19/95 animals (20%). Co-infection was detected in five animals. The cases were recorded across multiple geographic regions and throughout the sampling period. Univariate logistic regression analysis failed to identify any statistically significant risk factors for B. divergens presence. This study demonstrates that bovine babesiosis is geographically widespread throughout England and Wales, placing a large proportion of the cattle population at risk of infection, with the potential for zoonotic transmission to humans.

Prevalence of Babesia spp. pathogens in the ticks Dermacentor reticulatus and Ixodes ricinus in the UK

The emergence of Babesia pathogens novel to the UK is of growing concern; these include Babesia canis and Babesia caballi. However, a better understanding of changes in the prevalence of endemic Babesia species such as Babesia venatorum and Babesia divergens is also of importance. Here, the prevalence of Babesia pathogens in both Dermacentor reticulatus and Ixodes ricinus ticks was assessed. Dermacentor reticulatus were collected from six sites known to harbour populations of this species in west Wales and southern England. DNA was extracted from 879 individual ticks and subjected to PCR and sequence analysis. Seven Babesia species were detected in 7.5% of the ticks, including B. caballi (0.68%), B. bovis (1.7%), B. microti (1.02%), B. bigemina (0.34%), B. capreoli (0.34%), and one isolate of B. canis (0.34%). Two of the field sites with grazing equines present had ticks that were positive for B. caballi. For I. ricinus, up to 200 nymphs were collected from each of 24 cattle farms in south-west England. Nymphs were divided into 6 pools of 30 from each farm for DNA extraction, PCR, and sequencing. Samples from seven out of the 24 farms tested positive for Babesia, and most were positive for more than one species. Babesia divergens was identified from five farms, and three of these farms had two pooled samples positive for B. divergens, which given the low overall prevalence rate suggests that B. divergens may be highly clustered within the tick population. Most of the remaining positive samples were Babesia venatorum, demonstrating that this zoonotic pathogen is widespread in livestock habitats. The data suggest that B. canis is not yet widely prevalent in established D. reticulatus populations in the UK, but that there is a need to raise awareness of the risk of equine piroplasmosis in areas with endemic D. reticulatus foci, since B. caballi appears more widely established.

Animal reservoirs of zoonotic Babesia species: A global systematic review and meta-analysis of their prevalence, distribution and species diversity

Zoonotic babesiosis caused by Babesia divergens, B. microti and B. venatorum is a vector-borne protozoan zoonosis of increasing public health importance worldwide. A complex system of animal reservoirs including a wide range of mammals and a limited number of birds play a central role in maintaining the infection. Governed by the PRISMA guidelines, we conducted a systematic review and meta-analysis to determine the global prevalence, distribution and the diversity of zoonotic Babesia species in animal reservoirs. We pooled data using the random-effects model and determined quality of individual studies, heterogeneity and across study bias using the Joanna Briggs Institute critical appraisal instrument for prevalence studies, Cochran's Q-test and Egger's regression test respectively. Seventy nine studies from 29 countries reported a total 9311 positive cases of zoonotic Babesia infections from 46,649 animal reservoirs, yielding an overall estimated prevalence of 12.45% (95% CI: 10.09-15.27). Continental prevalence ranged between 8.55 (95% CI: 1.90-31.11) in Africa and 27.81% (95% CI: 21.25-35.48) in North America. Estimated prevalence in relation to country income levels, methods of diagnosis, study periods, sample sizes and reservoir categories ranged between 4.97 (95% CI: 1.80-13.00) and 30.12% (95% CI: 22.49-39.04). B. divergens was the most prevalent (12.50%, 95% CI: 8.30-18.39) of the 3 species of zoonotic Babesia reported in animal reservoirs. Zoonotic Babesia infections are prevalent in animal reservoirs across the world with the highest prevalence in North America and domestic animals. B. microti had the widest geographic distribution. We recommend tick control as well as strategic and prophylactic treatment against these parasites in animal reservoirs to curtail the economic losses associated with zoonotic Babesia species and possible transmission to humans.

Zoonotic Tick-Borne Pathogens in Temperate and Cold Regions of Europe-A Review on the Prevalence in Domestic Animals

Ticks transmit a variety of pathogens affecting both human and animal health. In temperate and cold regions of Europe (Western, Central, Eastern, and Northern Europe), the most relevant zoonotic tick-borne pathogens are tick-borne encephalitis virus (TBEV), Borrelia spp. and Anaplasma phagocytophilum. More rarely, Rickettsia spp., Neoehrlichia mikurensis, and zoonotic Babesia spp. are identified as a cause of human disease. Domestic animals may also be clinically affected by these pathogens, and, furthermore, can be regarded as sentinel hosts for their occurrence in a certain area, or even play a role as reservoirs or amplifying hosts. For example, viraemic ruminants may transmit TBEV to humans via raw milk products. This review summarizes the role of domestic animals, including ruminants, horses, dogs, and cats, in the ecology of TBEV, Borrelia spp., A. phagocytophilum, Rickettsia spp., N. mikurensis, and zoonotic Babesia species. It gives an overview on the (sero-)prevalence of these infectious agents in domestic animals in temperate/cold regions of Europe, based on 148 individual prevalence studies. Meta-analyses of seroprevalence in asymptomatic animals estimated an overall seroprevalence of 2.7% for TBEV, 12.9% for Borrelia burgdorferi sensu lato (s.l.), 16.2% for A. phagocytophilum and 7.4% for Babesia divergens, with a high level of heterogeneity. Subgroup analyses with regard to animal species, diagnostic test, geographical region and decade of sampling were mostly non-significant, with the exception of significantly lower B. burgdorferi s.l. seroprevalences in dogs than in horses and cattle. More surveillance studies employing highly sensitive and specific test methods and including hitherto non-investigated regions are needed to determine if and how global changes in terms of climate, land use, agricultural practices and human behavior impact the frequency of zoonotic tick-borne pathogens in domestic animals.

Molecular detection of Babesia divergens and Mycoplasma wenyonii infection in cattle from Bosnia And Herzegovina

We report two cases of bovine babesiosis caused by Babesia divergens in a region of central Bosnia and Herzegovina. The cases were detected in June 2017 and July 2018 from two small backyard farms. Routine clinical assessments, including physical examination and haematology, revealed lethargy, fever, anaemia, leukopenia and haemoglobinuria in the affected animals. Serum alterations included an elevation of aspartate aminotransferase and a decrease of serum phosphate or hypophosphatemia. Thrombocytopenia was detected in the first clinical case. Microscopic examination of blood smears revealed intracytoplasmic protozoan parasites from the genus Babesia. Molecular screening of both animals confirmed the presence of Babesia divergens, the causative agent of bovine babesiosis. B. divergens DNA was also detected in two engorged female Ixodes ricinus ticks removed from these animals. In addition, Mycoplasma wenyonii DNA was identified by molecular screening in the animal examined in June 2017, and in I. ricinus ticks feeding on this animal. This study provides molecular confirmation of B. divergens as a cause of piroplasmosis in cattle in South-East Europe. The detection of M. wenyonii DNA ain I. ricinus also provides the first evidence of this bacterium in ticks in Europe.

Changing incidence of bovine babesiosis in Ireland

BACKGROUND

In Ireland bovine babesiosis is caused by the tick-borne blood parasite, Babesia divergens. A survey of veterinary practitioners and farmers in the 1980's revealed an annual incidence of 1.7% associated with considerable economic losses. However, two subsequent surveys in the 1990's indicated a decline in clinical babesiosis. Recent evidence from continental Europe suggests that, probably due to climate change, the distribution of the tick vector of B. divergens, Ixodes ricinus is extending to more northerly regions and higher altitudes. In addition, milder winters are thought to widen the window of tick activity. In order to determine whether any such changes have affected the incidence of bovine babesiosis in Ireland, a questionnaire survey of farmers and veterinarians was carried out and compared with data from previous surveys.

RESULTS

Our survey indicates that while the incidence of clinical disease has continued to decline, cases can occur at any time of year. In contrast to previous surveys, affected farms were the same size as unaffected ones. There was no correlation between disease risk and the presence of deer on the land. Disease severity and mortality rates were increased because many infections were advanced by the time they were detected and treated.

CONCLUSION

While the precise reasons for the decline in the incidence of redwater are unknown, changes in agricultural practice are likely to be of importance. A reversal of the trend could be devastating, as vigilance among farmers and veterinarians is flagging and the national herd is losing its protective immunity to disease.

Modelling bovine babesiosis: a tool to simulate scenarios for pathogen spread and to test control measures for the disease

Tick-borne diseases are of increasing concern in many countries, particularly as a consequence of changes in land use and climate. Ticks are vectors of numerous pathogens (viruses, bacteria, protozoa) that can be harmful to humans and animals. In the context of animal health, bovine babesiosis poses a recurrent threat to cattle herds. In this study, we use a modeling approach to investigate the spread of babesiosis and evaluate control measures. A previously developed tick population dynamics model (here, Ixodes ricinus) is coupled with a pathogen spread model (here, the protozoan Babesia divergens), which describes pathogen spread in a dairy herd through the following processes: transmission, acquisition, transovarial transmission, transstadial persistence, and clearance of the pathogen. An assessment of the simulated B. divergens prevalence levels in ticks and cattle in the context of existing knowledge and data suggested that the model provides a realistic representation of pathogen spread. The model was then used to evaluate the influence of host density and the effect of acaricides on B. divergens prevalence in cattle. Increasing deer density results in an increase in prevalence in cattle whereas increasing cattle stocking rate results in a slight decrease. A potential increase in deer density would thus have an amplification effect on disease spread due to the increase in the number of infected ticks. Regular use of acaricides produces a reduction in pathogen prevalence in cattle. This model could be adapted to other tick-borne diseases.

A Vegetation Index qualifying pasture edges is related to Ixodes ricinus density and to Babesia divergens seroprevalence in dairy cattle herds

Babesia divergens, transmitted by the tick Ixodes ricinus, is the main agent of bovine piroplasmosis in France. This Apicomplexa often is present in asymptomatic carriers; however, clinical cases are rare. While numerous factors are known to influence tick density, no risk factor of contact with B. divergens has been identified for cattle. Our study aimed to explore whether a Vegetation Index could serve as an indirect indicator of within-herd B. divergens seroprevalence. In February 2007, blood samples were taken from all of the cows in 19 dairy cattle herds in Western France and IFAT serology was performed individually to measure B. divergens seroprevalence. The following spring, I. ricinus nymphs were collected by drag sampling along transects on the vegetation of each farm's pasture perimeters. Tick density was related significantly to a Vegetation Index (V.I., ranging from 1 to 5) that took into account the abundance of trees and bushes on the edge of pastures: most ticks (57%) were found in transects with the highest V.I. (covering 15% of the explored surface in the study area). At the farm level, the proportion of transects presenting I. ricinus nymphs was significantly related to B. divergens seroprevalence: the farms with more than 15% of transects with I. ricinus had a significantly higher risk of high seroprevalence. The proportion of pasture perimeters where the V.I.=5 also was significantly related to B. divergens seroprevalence: the farms where more than 20% of transects had a V.I.=5 had a significantly higher risk of high seroprevalence. Given that the Vegetation Index is a steady indicator of the potential I. ricinus density in the biotope, we recommend that the risk of high B. divergens seroprevalence in cows be evaluated using this tool rather than drag samplings.

Detection of Babesia divergens in southern Norway by using an immunofluorescence antibody test in cow sera

BACKGROUND

The incidence of bovine babesiosis, caused by Babesia divergens (Apicomplexa: Piroplasmida) has decreased markedly since the 1930 s, but may re-emerge as a consequence of climate change and changes in legislation and pasturing practices. This is a potentially serious disease, with both economical and animal welfare consequences. Therefore, there is a need to survey the distribution of B. divergens.

METHODS

We tested sera from 306 healthy pastured cows from 24 farms along the southern Norwegian coast by using an indirect immunofluorescence IgG antibody test (IFAT). Fractions of seropositive cows were compared by calculating 95% CI.

RESULTS

The results of this test showed that 27% of the sera were positive for B. divergens antibodies. The fraction of antibody-positive sera that we detected showed a two-humped distribution, with a high fraction of positives being found in municipalities in the western and eastern parts of the study area, while the municipalities between these areas had few or no positive serum samples.

CONCLUSIONS

Neither the farmers' observations nor the Norwegian Dairy Herd Recording System give an adequate picture of the distribution of bovine babesiosis. Serological testing of cows by using IFAT is a convenient way of screening for the presence of B. divergens in an area.

Babesia divergens, a bovine blood parasite of veterinary and zoonotic importance

Babesia divergens is an intraerythrocytic protozoan parasite, transmitted by the tick Ixodes ricinus, and is the main agent of bovine babesiosis in Europe. It is not only a cause of significant loss to the cattle industry; it can also infect immunocompromised humans, causing medical emergencies characterized by rapid fulmination and parasitemias that may exceed 70%. The current emphasis in Europe on sustainable agriculture and extensification is likely to lead to an increase in vector tick populations with increased risk of infection. Despite the veterinary and zoonotic importance of this parasite, relatively little research has been carried out on B. divergens, and many questions regarding the parasite's epidemiology and the host's response remain unanswered. A better understanding of the species' biology and host-parasite interactions may lead to improved control mechanisms and new trends in vaccine and antibabesial drug development. This review provides the first comprehensive summary of B. divergens biology, including its morphology, life cycle, and host specificity, and the current state of knowledge of both human and bovine infections.

Piroplasms of domestic animals in the Macedonia region of Greece. 2. Piroplasms of cattle

A study was carried out on piroplasms of cattle in the Macedonia region of Greece. During 1984-1986, 602 serum samples were collected from cattle in 33 localities. Blood smears were also prepared from 50 of the animals in 13 localities. The indirect fluorescent antibody (IFA) test revealed that 41.4% of cattle sera were positive to Theileria orientalis, 2.0% to Theileria annulata, 21.6% to Babesia bovis, 15.2% to Babesia bigemina, 5.1% to Babesia major and 2.7% to Babesia divergens. Some of the positive titres were probably due to cross reactions. T. orientalis was widely distributed. T. annulata was limited to a small number of foci. B. bigemina and B. bovis, often present together, were widespread, whereas B. major was only present in a small number of localities. No convincing evidence of B. divergens infection was found. By examination of Giemsa stained blood smears T. orientalis, T. annulata and a Babesia sp. were detected.

Studies on the use of gerbil-derived Babesia divergens antigen for diagnosis of bovine babesiosis

Babesia divergens antigen obtained from bovine and gerbil erythrocytes was compared for the diagnosis of bovine babesiosis by the indirect immunofluorescence antibody test (IFAT) and the enzyme-linked immunosorbent assay (ELISA). Using a range of sera from the field and from experimental cattle, it was found that antigen from the two sources did not differ significantly in sensitivity or specificity. Antigen from gerbils may, therefore, be used for serological surveys of bovine babesiosis caused by B. divergens. The IFAT and ELISA were also compared and it was concluded that they are equally effective in the detection of positive samples. For small-scale surveys, the IFAT using gerbil-derived antigen is adequate, but for large surveys the ELISA is preferable.

Babesiosis: under-reporting or case-clustering?

Babesiosis is a tick-borne protozoan disease which principally affects animals but occasionally affects humans. Cases have been reported from many parts of Europe with no evidence of case-clustering. We report the second case of babesiosis from a small area in the west of Ireland.