Prevalence and Genetic Diversity of Anaplasma marginale Strains in Cattle in South Africa

Anaplasma Species in Africa-A Century of Discovery: A Review on Molecular Epidemiology, Genetic Diversity, and Control

Anaplasma species, belonging to the family Anaplasmataceae in the order Rickettsiales, are obligate intracellular bacteria responsible for various tick-borne diseases of veterinary and human significance worldwide. With advancements in molecular techniques, seven formal species of Anaplasma and numerous unclassified species have been described. In Africa, several Anaplasma species and strains have been identified in different animals and tick species. This review aims to provide an overview of the current understanding of the molecular epidemiology and genetic diversity of classified and unclassified Anaplasma species detected in animals and ticks across Africa. The review also covers control measures that have been taken to prevent anaplasmosis transmission on the continent. This information is critical when developing anaplasmosis management and control programs in Africa.

Temporal Dynamics of Anaplasma marginale Infections and the Composition of Anaplasma spp. in Calves in the Mnisi Communal Area, Mpumalanga, South Africa

Bovine anaplasmosis, caused by Anaplasma marginale, is one of the most important tick-borne diseases of cattle. Anaplasma marginale is known to be present in the Mnisi community, Mpumalanga Province, with frequent cases of anaplasmosis reported. This study investigated the infection dynamics in calves (n = 10) in two habitats in the study area over 12 months. A duplex real-time PCR assay targeting the msp1β gene of A. marginale and the groEL gene of A. centrale confirmed the presence of A. marginale in five calves in a peri-urban area from the first month, but in only two calves at the wildlife-livestock interface and only after six months. These results were confirmed by 16S rRNA microbiome analysis. Over 50 A. marginale msp1α genotypes were detected in the calves along with five novel Msp1a repeats. Calves in the peri-urban area were more likely to be infected with A. marginale than calves in the wildlife-livestock interface. Cattle management, acaricide treatment, and cattle density could explain differences in infection prevalence in the two areas. Our results revealed that most calves were superinfected by distinct A. marginale strains within the study period, indicating continuous challenge with multiple strains that should lead to robust immunity in the calves and endemic stability in the area.

Epidemiology of Ticks and Tick-Borne Pathogens in Domestic Ruminants across Southern African Development Community (SADC) Region from 1980 until 2021: A Systematic Review and Meta-Analysis

Ticks are hematophagous ectoparasites that are capable of infesting a wide range of mammals, including domestic animals, ruminants, wildlife, and humans across the world, and they transmit disease-causing pathogens. Numerous individual epidemiological studies have been conducted on the distribution and prevalence of ticks and tick-borne diseases (TBDs) in the Southern African Developing Community (SADC) region, but no effort has been undertaken to synchronize findings, which would be helpful in the implementation of consolidated tick control measures. With the aim of generating consolidated pooled prevalence estimates of ticks and TBDs in the SADC region, we performed a systematic review and meta-analysis of published articles using the PRISMA 2020 guidelines. A deep search was performed on five electronic databases, namely, PubMed, ScienceDirect, Google Scholar, AJOL, and Springer Link. Of the 347 articles identified, only 61 of the articles were eligible for inclusion. In total, 18,355 tick specimens were collected, belonging to the genera Amblyomma, Haemaphysalis, Hyalomma, and Rhipicephalus (including Boophilus) across several countries, including South Africa (n = 8), Tanzania (n = 3), Zambia (n = 2), Zimbabwe (n = 2), Madagascar (n = 2), Angola (n = 2), Mozambique (n = 1), and Comoros (n = 1). The overall pooled prevalence estimate (PPE) of TBPs in livestock was 52.2%, with the highest PPE in cattle [51.2%], followed by sheep [45.4%], and goats [29.9%]. For bacteria-like and rickettsial TBPs, Anaplasma marginale had the highest PPE of 45.9%, followed by A. centrale [14.7%], A. phagocytophilum [2.52%], and A. bovis [0.88%], whilst Ehrlichia ruminantium had a PPE of 4.2%. For piroplasmids, Babesia bigemina and B. bovis had PPEs of 20.8% and 20.3%, respectively. Theileria velifera had the highest PPE of 43.0%, followed by T. mutans [29.1%], T. parva [25.0%], and other Theileria spp. [14.06%]. Findings from this study suggest the need for a consolidated scientific approach in the investigation of ticks, TBPs, and TBDs in the whole SADC region, as most of the TBDs are transboundary and require a regional control strategy.

Screening and Analysis of Anaplasma marginale Tunisian Isolates Reveal the Diversity of lipA Phylogeographic Marker and the Conservation of OmpA Protein Vaccine Candidate

Bovine anaplasmosis caused by Anaplasma marginale is a disease responsible for serious animal health problems and great economic losses all over the world. Thereby, the identification of A. marginale isolates from various bioclimatic areas in each country, the phylogeographic analysis of these isolates based on the most informative markers, and the evaluation of the most promising candidate antigens are crucial steps in developing effective vaccines against a wide range of A. marginale strains. In order to contribute to this challenge, a total of 791 bovine samples from various bioclimatic areas of Tunisia were tested for the occurrence of A. marginale DNA through msp4 gene fragment amplification. Phylogeographic analysis was performed by using lipA and sucB gene analyses, and the genetic relationship with previously characterized A. marginale isolates and strains was analyzed by applying similarity comparison and phylogenetic analysis. To evaluate the conservation of OmpA protein vaccine candidate, almost complete ompA nucleotide sequences were also obtained from Tunisian isolates, and various bioinformatics software were used in order to analyze the physicochemical properties and the secondary and tertiary structures of their deduced proteins and to predict their immunodominant epitopes of B and T cells. A. marginale DNA was detected in 19 bovine samples (2.4%). Risk factor analysis shows that cattle derived from subhumid bioclimatic area were more infected than those that originated from other areas. The analysis of lipA phylogeographic marker indicated a higher diversity of Tunisian A. marginale isolates compared with other available worldwide isolates and strains. Molecular, phylogenetic, and immuno-informatics analyses of the vaccine candidate OmpA protein demonstrated that this antigen and its predicted immunodominant epitopes of B and T cells appear to be highly conserved between Tunisian isolates and compared with isolates from other countries, suggesting that the minimal intraspecific modifications will not affect the potential cross-protective capacity of humoral and cell-mediated immune responses against multiple A. marginale worldwide strains.

Anaplasma marginale outer membrane protein vaccine candidates are conserved in North American and South African strains

Bovine anaplasmosis is a globally economically important tick-borne disease caused by the obligate intraerythrocytic rickettsia, Anaplasma marginale. A live Anaplasma centrale blood-based vaccine is available, but it does not protect against all A. marginale field strains and may also transmit other blood-borne pathogens. Five potential outer membrane protein (OMP) vaccine candidates have been well-characterised in A. marginale strains from the USA, however, their levels of conservation in other countries must be ascertained in order to inform their use in a vaccine with regional or global efficacy. This study assessed the amino acid variation in vaccine candidate OMPs in South African strains of A. marginale, and also compared the immunogenic properties between South African and US strains. OMP genes Am779, Am854, omp7, omp8 and omp9 were amplified and sequenced from a set of genetically diverse South African samples with different msp1α-genotypes. OMPs Am854 and Am779 were highly conserved, with 99-100 % amino acid identity, while Omp7, Omp8 and Omp9 had 79-100 % identity with US strains. As has been shown previously, Omp7-9 possess conserved N- and C- termini, a central variable region, and a highly conserved CD4 T-cell epitope, FLLVDDA(I/V)V, in the N-terminal region. Western blot analysis of recombinant OMPs indicates strong antigenic conservation between South African and US strains of A. marginale, suggesting that they are good candidates for use in a novel global vaccine cocktail, although further work on the best formulation and delivery methods will be necessary.

Genetic characterization of tick-borne pathogens in ticks infesting cattle and sheep from three South African provinces

Ticks are involved in the transmission of many public health and veterinary important pathogens. Although tick-borne pathogens are widely distributed in South Africa, information on tick-pathogen relationship needs to be updated particularly using modern molecular techniques. This study used PCR and sequencing to confirm the identity of the tick species collected from cattle and sheep from KwaZulu-Natal, Free State and Eastern Cape. Furthermore, presence of Babesia spp., Theileria spp., Anaplasma marginale, Rickettsia spp., Ehrlichia ruminantium and Coxiella burnetii was detected from tick DNA using species-specific PCR or nested PCRs. The study samples consisted of 390 adult ticks (male and female) which were pooled according to species, host animal and sampling site (three ticks per pool) for DNA extraction. The PCR results revealed that out of 130 tick DNA pools, 30 (23.1%) were positive for at least one pathogen. The most frequent pathogen was C. burnetii (9.2%), followed by Rickettsia spp. (7.7%), A. marginale (3.8%), T. mutans (3.1%), T. taurotragi (2.3%) and E. ruminantium (1.5%). The highest prevalence of pathogens was observed in ticks collected from cattle in Eastern Cape (16/42) and the lowest was in ticks obtained from sheep in Free State (1/21). Infected ticks were identified as Rhipicephalus evertsi evertsi (n = 13), R. appendiculatus (n = 3), R. decoloratus (n = 7) and Amblyomma hebraeum (n = 7). Coinfection with two pathogens was found in 21% of pathogen-positive pools. Analysis of Theileria taurotragi 18S rRNA, T. mutans 18S rRNA, C. burnetii htpB, Rickettsia spp. gltA, Rickettsia spp. ompA, E. ruminantium pCS20 and A. marginale Msp5 sequences showed that the pathogens detected in this study were genetically related to isolates previously reported in Africa. These findings provide important information on distribution of ticks and tick-borne pathogens of ruminants and will contribute in the formulation of future control strategies in South Africa.

Prevalence of Anaplasma species in India and the World in dairy animals: A systematic review and meta-analysis

In the present study, the prevalence of Anaplasma species in diary animals from India and World was estimated using meta-analysis. Based on systematic review of studies on Anaplasma species from India [35] and World [66] from 1988 to 2017 and 1978-2017, respectively, using online databases and offline literatures, meta-analysis using meta package in R-Software was done. Prevalence of Anaplasma species in India and World were 11% [95% level, Confidence Interval[CI] 7-16%, Prediction Interval[PI] 1-69%] and 39% [95% level, CI 30-49%, PI 2-95%], and these were obtained using 31,117 and 46,365 samples, respectively. Period-wise analysis revealed high Anaplasma species prevalence before 2011 for India and the World than from 2011 through 2017. Zone-wise prevalence indicated high prevalence in Central zone [61%] and low in West and South zones [6%] in India, and continent-wise, it was high in South America [82%]. The studies used methods including blood smear examination, serology and nucleic acid-based techniques and revealed high prevalence in serology for India [34%] and World [46%], low prevalence by blood smear for India [7%] and World [21%], but higher sensitivity using nucleic acid-based techniques. Species-wise indicated higher prevalence in cattle [12%] than buffaloes [2%] in India. Prevalence was lower in India compared to the World and higher in South America. Overall, anaplasmosis causes low productivity in dairy animals and economic loss to dairy farmers. Hence, there is a need to control Anaplasma infections in high risk areas by adopting effective therapeutic and preventive measures so as to improve the economic benefits in dairy farming.

Serological evidence of exposure to some zoonotic microorganisms in cattle and humans with occupational exposure to livestock in Antioquia, Colombia

Bacteria belonging to Anaplasma, Ehrlichia, Rickettsia and Coxiella genera are considered emerging pathogens and livestock is one of the contexts where the transmission of these microorganisms can occur. The goal of this study was to determine serological evidence for the exposure to these bacteria in cattle and humans with occupational exposure to livestock in the subregions North and Magdalena Medio, Antioquia, Colombia, and to explore related factors. A cross-sectional study was conducted in 48 livestock farms distributed in six municipalities from both subregions: Belmira, Entrerríos and San Pedro de los Milagros (North), and Puerto Berrío, Puerto Nare and Puerto Triunfo (Magdalena Medio). Blood samples from 332 people and 384 bovines were evaluated by serology (IgM and IgG) screening for bacteria from the Anaplasma, Ehrlichia, Rickettsia, and Coxiella genera. Seropositivity in humans from both regions was 42.4% (95%CI: 31.2-55.1) for Anaplasma, 74.2% (95%CI: 66.0-84.4) for Ehrlichia, 72.5% (95%CI: 62.1-82.0) for Rickettsia, and 60.7% (95%CI: 59.7-69.1) for Coxiella burnetii. In cattle, seropositivity was 31.6% (95%CI: 19.9-44.2), 66.8% (95%CI: 55.2-78.1), 64.6% (95%CI: 53.8-74.5), and 61.6% (95%CI: 51.9-69.2), respectively. History of biting by ticks, milking, vaccination, having dogs and hens in the residence, as well as the consumption of raw milk derivatives were some factors associated with the infection by the bacteria studied. The results suggest a previous and recent exposure to these zoonotic bacteria genera in people with occupational exposure to livestock, as well as in cattle in the two studied subregions.

Evidence confirming the phylogenetic position of Anaplasma centrale (ex Theiler 1911) Ristic and Kreier 1984

In 1911, Sir Arnold Theiler isolated and described a parasite that was very similar to Anaplasma marginale but which was more centrally located within the erythrocytes of the host cells, and was much less pathogenic than A. marginale. He named the parasite A. marginale variety centrale. The name Anaplasma centrale, referring to the same organism, was published in Validation List No. 15 in 1984, but the publication was based on an erroneous assumption that Theiler had indicated that it was a separate species. Many authors have subsequently accepted this organism as a separate species, but evidence to indicate that it is a distinct species has never been presented. The near full-length 16S rRNA gene sequence, and the deduced amino acid sequences for groEL and msp4 from several isolates of A. marginale and A. centrale from around South Africa were compared with those of the A. marginale type strain, St Maries, and the A. centrale Israel strain and other reference sequences. Phylogenetic analyses of these sequences demonstrated that A. centrale consistently forms a separate clade from A. marginale, supported by high bootstrap values (≥90 %), revealing that there is divergence between these two organisms. In addition, we discuss distinctive characteristics which have been published recently, such as differences in Msp1a/Msp1aS gene structure, as well as genome architecture that provide further evidence to suggest that A. centrale is, in fact, a separate species. Our results, therefore, provide evidence to support the existing nomenclature, and confirm that A. centrale (ex Theiler 1911) Ristic and Kreier 1984 is, indeed, a distinct species.

Detection and Characterisation of Anaplasma marginale and A. centrale in South Africa

Bovine anaplasmosis is endemic in South Africa and it has a negative economic impact on cattle farming. An improved understanding of Anaplasma marginale and Anaplasma marginale variety centrale (A. centrale) transmission, together with improved tools for pathogen detection and characterisation, are required to inform best management practices. Direct detection methods currently in use for A. marginale and A. centrale in South Africa are light microscopic examination of tissue and organ smears, conventional, nested, and quantitative real-time polymerase chain reaction (qPCR) assays, and a reverse line blot hybridisation assay. Of these, qPCR is the most sensitive for detection of A. marginale and A. centrale in South Africa. Serological assays also feature in routine diagnostics, but cross-reactions prevent accurate species identification. Recently, genetic characterisation has confirmed that A. marginale and A. centrale are separate species. Diversity studies targeting Msp1a repeats for A. marginale and Msp1aS repeats for A. centrale have revealed high genetic variation and point to correspondingly high levels of variation in A. marginale outer membrane proteins (OMPs), which have been shown to be potential vaccine candidates in North American studies. Information on these OMPs is lacking for South African A. marginale strains and should be considered in future recombinant vaccine development studies, ultimately informing the development of regional or global vaccines.

Co-infections with multiple genotypes of Anaplasma marginale in cattle indicate pathogen diversity

BACKGROUND

Only a few studies have examined the presence of Anaplasma marginale and Anaplasma centrale in South Africa, and no studies have comprehensively examined these species across the whole country. To undertake this country-wide study we adapted a duplex quantitative real-time PCR (qPCR) assay for use in South Africa but found that one of the genes on which the assay was based was variable. Therefore, we sequenced a variety of field samples and tested the assay on the variants detected. We used the assay to screen 517 cattle samples sourced from all nine provinces of South Africa, and subsequently examined A. marginale positive samples for msp1α genotype to gauge strain diversity.

RESULTS

Although the A. marginale msp1β gene is variable, the qPCR functions at an acceptable efficiency. The A. centrale groEL gene was not variable within the qPCR assay region. Of the cattle samples screened using the assay, 57% and 17% were found to be positive for A. marginale and A. centrale, respectively. Approximately 15% of the cattle were co-infected. Msp1α genotyping revealed 36 novel repeat sequences. Together with data from previous studies, we analysed the Msp1a repeats from South Africa where a total of 99 repeats have been described that can be attributed to 190 msp1α genotypes. While 22% of these repeats are also found in other countries, only two South African genotypes are also found in other countries; otherwise, the genotypes are unique to South Africa.

CONCLUSIONS

Anaplasma marginale was prevalent in the Western Cape, KwaZulu-Natal and Mpumalanga and absent in the Northern Cape. Anaplasma centrale was prevalent in the Western Cape and KwaZulu-Natal and absent in the Northern Cape and Eastern Cape. None of the cattle in the study were known to be vaccinated with A. centrale, so finding positive cattle indicates that this organism appears to be naturally circulating in cattle. A diverse population of A. marginale strains are found in South Africa, with some msp1α genotypes widely distributed across the country, and others appearing only once in one province. This diversity should be taken into account in future vaccine development studies.

Anaplasma infection prevalence in beef and dairy cattle in the south east region of Botswana

Infection of cattle by the tick-borne intra-erythrocytic bacteria of the genus Anaplasma occurs worldwide. Nevertheless, prevalence rates in specific regions are still required to inform cattle farming management decisions. A study was carried out to determine Anaplasma infection prevalence in beef and dairy cattle in the south east region of Botswana. Two methods were used: competitive inhibition enzyme-linked immune-sorbent assay (cELISA) and conventional polymerase chain reaction (PCR). A total of 429 cattle consisting 207 beef and 222 dairy animals were sampled and tested. The prevalence was 91% and 31% by cELISA and PCR, respectively. A Z test revealed a statistical difference between the point prevalence as determined by cELISA compared to PCR (p=0). There was no statistical difference between the point prevalence of Anaplasma infection as determined by cELISA (p=0.45) between beef and dairy cattle. But there was a significant difference (p=0.001) between the animals by PCR with the prevalence in beef cattle nearly double that in dairy cattle. Individual herd prevalence ranged from 79% to 100% by cELISA, and 0 to 100% by PCR. Though not statistically significant sero-prevalence in both beef and dairy animals tended to be higher in urban/peri-urban areas compared to rural areas. The cELISA mean percentage inhibition (PI) for all cattle was found to be 58.6 (95% CI: 56.8-60.4). There was no statistically significant difference between the mean PI of sera from beef cattle (56.4 (95% CI: 54.1-58.7)) as compared to dairy cattle (60.7 (95%CI: 58.0-63.3)). However, there was a tendency towards statistical significance with beef animals having a lower PI value than dairy animals. Anaplasma infection was endemic in cattle in the south east region of Botswana with similar infection in beef and dairy animals. Further research should be done to identify the strains prevalent in the cattle herds.

Comparison of three nucleic acid-based tests for detecting <i>Anaplasma marginale</i> and <i>Anaplasma centrale</i> in cattle

Several nucleic acid-based assays have been developed for detecting Anaplasma marginale and Anaplasma centrale in vectors and hosts, making the choice of method to use in endemic areas difficult. We evaluated the ability of the reverse line blot (RLB) hybridisation assay, two nested polymerase chain reaction (nPCR) assays and a duplex real-time quantitative polymerase chain reaction (qPCR) assay to detect A. marginale and A. centrale infections in cattle (n = 66) in South Africa. The lowest detection limits for A. marginale plasmid DNA were 2500 copies by the RLB assay, 250 copies by the nPCR and qPCR assays and 2500, 250 and 25 copies of A. centrale plasmid DNA by the RLB, nPCR and qPCR assays respectively. The qPCR assay detected more A. marginale- and A. centrale-positive samples than the other assays, either as single or mixed infections. Although the results of the qPCR and nPCR tests were in agreement for the majority (38) of A. marginale-positive samples, 13 samples tested negative for A. marginale using nPCR but positive using qPCR. To explain this discrepancy, the target sequence region of the nPCR assay was evaluated by cloning and sequencing the msp1β gene from selected field samples. The results indicated sequence variation in the internal forward primer (AM100) area amongst the South African A. marginale msp1β sequences, resulting in false negatives. We propose the use of the duplex qPCR assay in future studies as it is more sensitive and offers the benefits of quantification and multiplex detection of both Anaplasma spp.

Characterization of Anaplasma marginale subsp. centrale Strains by Use of msp1aS Genotyping Reveals a Wildlife Reservoir

Bovine anaplasmosis caused by the intraerythrocytic rickettsial pathogen Anaplasma marginale is endemic in South Africa. Anaplasma marginale subspecies centrale also infects cattle; however, it causes a milder form of anaplasmosis and is used as a live vaccine against A. marginale There has been less interest in the epidemiology of A. marginale subsp. centrale, and, as a result, there are few reports detecting natural infections of this organism. When detected in cattle, it is often assumed that it is due to vaccination, and in most cases, it is reported as coinfection with A. marginale without characterization of the strain. A total of 380 blood samples from wild ruminant species and cattle collected from biobanks, national parks, and other regions of South Africa were used in duplex real-time PCR assays to simultaneously detect A. marginale and A. marginale subsp. centrale. PCR results indicated high occurrence of A. marginale subsp. centrale infections, ranging from 25 to 100% in national parks. Samples positive for A. marginale subsp. centrale were further characterized using the msp1aS gene, a homolog of msp1α of A. marginale, which contains repeats at the 5' ends that are useful for genotyping strains. A total of 47 Msp1aS repeats were identified, which corresponded to 32 A. marginale subsp. centrale genotypes detected in cattle, buffalo, and wildebeest. RepeatAnalyzer was used to examine strain diversity. Our results demonstrate a diversity of A. marginale subsp. centrale strains from cattle and wildlife hosts from South Africa and indicate the utility of msp1aS as a genotypic marker for A. marginale subsp. centrale strain diversity.

RepeatAnalyzer: a tool for analysing and managing short-sequence repeat data

Background

Short-sequence repeats (SSRs) occur in both prokaryotic and eukaryotic DNA, inter- and intragenically, and may be exact or inexact copies. When heterogeneous SSRs are present in a given locus, we can take advantage of the pattern of different repeats to genotype strains based on the SSRs. Cataloguing and tracking these repeats can be difficult as diverse groups of researchers are involved in the identification of the repeats. Additionally, the task is error-prone when done manually.

Results

We developed RepeatAnalyzer, a new software tool capable of tracking, managing, analysing and cataloguing SSRs and genotypes using Anaplasma marginale as a model species. RepeatAnalyzer’s analysis capability includes novel metrics for measuring regional genetic diversity (corresponding to variety and regularity of SSR occurrence). As a part of its visualization capabilities, RepeatAnalyzer produces high quality maps of the geographic distribution of genotypes or SSRs over a region of interest. RepeatAnalyzer’s repeat identification functionality was validated for all SSRs and genotypes reported in 21 publications, using 380 A. marginale isolates gathered from the five publications within that list that provided access to their isolates. The tool produced accurate genotyping results in every case. In addition, it uncovered a number of errors in the published literature: 11 cases where SSRs were misreported, 5 cases where two different SSRs had been given the same name, and 16 cases where two or more names had been given to a single SSR. The analysis and visualization functionalities of the tool are demonstrated using several examples.

Conclusions

RepeatAnalyzer is a robust software tool that can be used for storing, managing, and analysing short-sequence repeats for the purpose of strain identification. The tool can be used for any set of SSRs regardless of species. When applied to A. marginale, our test case, we show that genotype lengths for a given region follow a normal distribution, while SSR frequencies follow a power-law-like distribution. Further, we find that over 90 % of repeats are 28 to 29 amino acids long, which is in agreement with conventional wisdom. Lastly, our analysis reveals that the most common edit distance is five or six, which is counter-intuitive since we expected that result to be closer to one, resulting from the simplest change from one repeat to another.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2686-2) contains supplementary material, which is available to authorized users.

First molecular survey and novel genetic variants' identification of Anaplasma marginale, A. centrale and A. bovis in cattle from Tunisia

Few data are available about the presence and distribution of Anaplasma species in cattle in North African countries. In this study prevalence, co-infections, risk factors and genetic diversity of Anaplasma species were evaluated in bovines from Northern Tunisia. A total of 232 cattle from 36 randomly selected farms in three Tunisian localities were investigated for the presence of Anaplasma species in blood by Real-time PCR and/or nested PCR. Overall infection rates of Anaplasma spp., Anaplasma marginale, Anaplasma centrale and Anaplasma bovis were 34.9%, 25.4%, 15.1%, and 3.9%, respectively. Anaplasma phagocytophilum was not detected in cattle. The most common co-infection pattern was an association of A. marginale and A. centrale (11.2%). Five cattle (2.1%) all reared in the sub-humid bioclimatic area, were co-infected by the three Anaplasma species. Molecular prevalence of Anaplasma infection varied significantly according to locality, bioclimatic area, tick infestation and type of breeding. Animals of the Holstein breed were less infected by A. marginale and A. centrale than other breeds. Genetic analysis of A. marginale msp4 gene indicated a high sequence diversity of Tunisian strains, suggesting a multiple introduction of infected cattle from different origins. Phylogenetic studies based on the 16S rRNA gene showed that the most prevalent A. centrale strains were closely related to the A. centrale vaccine strain. Moreover, all A. bovis variants clustered with other A. bovis sequences obtained from domestic and wild ruminant strains. This is the first molecular investigation on Anaplasma species in Tunisian cattle providing pivotal background for designing epidemiological studies and to develop control strategies in the country.

Fecal shedding of thermophilic Campylobacter in a dairy herd producing raw milk for direct human consumption

Factors affecting the fecal shedding of thermophilic Campylobacter in Italian dairy farms were investigated in a 12-month longitudinal study performed on a dairy farm authorized to sell raw milk in Italy. Fifty animals were randomly selected from 140 adult and young animals, and fecal samples were collected six times at 2-month intervals. At each sampling time, three trough water samples and two trough feed samples also were collected for both adult and young animals. Samples were analyzed with real-time PCR assay and culture examination. Overall, 33 samples (9.7%) were positive for thermophilic Campylobacter by real-time PCR: 26 (9.2%) of 280 fecal samples, 6 (16.6%) of 36 water samples, and 1 (4.2%) of 24 feed samples. Campylobacter jejuni was isolated from 6 of 280 samples; no other Campylobacter species was isolated. A higher (but not significantly) number of positive fecal samples were found in younger animals (11.33 versus 6.92% of adult animals), and a significantly higher number of positive water samples were collected from the water troughs of young animals. A distinct temporal trend was observed during the study period for both cows and calves, with two prevalence peaks between November and December and between May and July. Several factors such as calving, housing practices, herd size, management practices forcing together a higher number of animals, and variations in feed or water sources (previously reported as a cause of temporal variation in different farming conditions) were excluded as the cause of the two seasonal peaks in this study. The factors affecting the seasonality of Campylobacter shedding in the dairy herds remain unclear and warrant further investigation. The results of the present study indicate that special attention should be paid to farm hygiene management on farms authorized to produce and sell raw milk, with increased surveillance by the authorities at certain times of the year.

Four-year monitoring of foodborne pathogens in raw milk sold by vending machines in Italy

Prevalence data were collected from official microbiological records monitoring four selected foodborne pathogens (Salmonella, Listeria monocytogenes, Escherichia coli O157:H7, and Campylobacter jejuni) in raw milk sold by self-service vending machines in seven Italian regions (60,907 samples from 1,239 vending machines) from 2008 to 2011. Data from samples analyzed by both culture-based and real-time PCR methods were collected in one region. One hundred raw milk consumers in four regions were interviewed while purchasing raw milk from vending machines. One hundred seventy-eight of 60,907 samples were positive for one of the four foodborne pathogens investigated: 18 samples were positive for Salmonella, 83 for L. monocytogenes, 24 for E. coli O157:H7, and 53 for C. jejuni in the seven regions investigated. No significant differences in prevalence were found among regions, but a significant increase in C. jejuni prevalence was observed over the years of the study. A comparison of the two analysis methods revealed that real-time PCR was 2.71 to 9.40 times more sensitive than the culture-based method. Data on consumer habits revealed that some behaviors may enhance the risk of infection linked to raw milk consumption: 37% of consumers did not boil milk before consumption, 93% never used an insulated bag to transport raw milk home, and raw milk was consumed by children younger than 5 years of age. These results emphasize that end-product controls alone are not sufficient to guarantee an adequate level of consumer protection. The beta distribution of positive samples in this study and the data on raw milk consumer habits will be useful for the development of a national quantitative risk assessment of Salmonella, L. monocytogenes, E. coli O157, and C. jejuni infection associated with raw milk consumption.

The influence of interspecific competition and host preference on the phylogeography of two African ixodid tick species

A comparative phylogeographic study on two economically important African tick species, Amblyomma hebraeum and Hyalomma rufipes was performed to test the influence of host specificity and host movement on dispersion. Pairwise AMOVA analyses of 277 mtDNA COI sequences supported significant population differentiation among the majority of sampling sites. The geographic mitochondrial structure was not supported by nuclear ITS-2 sequencing, probably attributed to a recent divergence. The three-host generalist, A. hebraeum, showed less mtDNA geographic structure, and a lower level of genetic diversity, while the more host-specific H. rufipes displayed higher levels of population differentiation and two distinct mtDNA assemblages (one predominantly confined to South Africa/Namibia and the other to Mozambique and East Africa). A zone of overlap is present in southern Mozambique. A mechanistic climate model suggests that climate alone cannot be responsible for the disruption in female gene flow. Our findings furthermore suggest that female gene dispersal of ticks is more dependent on the presence of juvenile hosts in the environment than on the ability of adult hosts to disperse across the landscape. Documented interspecific competition between the juvenile stages of H. rufipes and H. truncatum is implicated as a contributing factor towards disrupting gene flow between the two southern African H. rufipes genetic assemblages.

Quantitative risk assessment of verocytotoxin-producing Escherichia coli O157 and Campylobacter jejuni related to consumption of raw milk in a province in Northern Italy

A quantitative risk assessment was developed to describe the risk of campylobacteriosis and hemolytic uremic syndrome (HUS) linked to consumption of raw milk sold in vending machines in Northern Italy. Exposure assessment considered the microbiological status of dairy farms, expected milk contamination, storage conditions from bulk tank to home storage, microbial growth during storage, destruction experiments, consumption frequency of raw milk, age of consumers, serving size, and consumption preference. The differential risk between milk handled under regulation conditions (4°C throughout all phases) and the worst field handling conditions was considered. The probability of Campylobacter jejuni infection was modeled with a single-hit dose-response beta-Poisson model, whereas for HUS an exponential dose-response model was chosen and two probabilities were used to model the higher susceptibility of children younger than 5 years old. For every 10,000 to 20,000 consumers each year, the models predicted for the best and worst storage conditions, respectively, 2.12 and 1.14 campylobacteriosis cases and 0.02 and 0.09 HUS cases in the 0- to 5-year age group and 0.1 and 0.5 HUS cases in the >5-year age group. The expected pediatric HUS cases do not differ considerably from those reported in Italy by the Minister of Health. The model developed may be a useful tool for extending the assessment of the risk of campylobacteriosis and HUS due to raw milk consumption at the national level in Italy. Considering the epidemiological implications of this study, the risk of illness linked to raw milk consumption should not be ignored and could be reduced by the use of simple measures. Boiling milk before consumption and strict control of temperatures by farmers during raw milk distribution have significant effects on campylobacteriosis and HUS and are essential measures for risk management.

Foodborne pathogens in in-line milk filters and associated on-farm risk factors in dairy farms authorized to produce and sell raw milk in northern Italy

All dairy farms authorized to produce and sell raw milk in a province of Northern Italy were investigated to determine the presence of Campylobacter spp., verocytotoxin-producing Escherichia coli (VTEC), Listeria monocytogenes, and Salmonella spp. in in-line milk filters and to assess their association with suspected risk factors on farms. A logistic regression model was used to analyze data collected describing the characteristics and management practices of 27 farms and the microbiological status of 378 in-line milk filters by both culture-based and molecular methods. Thermotolerant Campylobacter, VTEC, and L. monocytogenes were detected in 24 (6.45%), 32 (8.4%), and 2 (0.5%) samples, respectively. No Salmonella spp. were detected. For risk analysis, data of L. monocytogenes and Salmonella spp. were not included in the model because of the low prevalence or absence of these organisms. The univariate analysis disclosed that the presence of VTEC and/or Campylobacter spp. in milk filters was associated with lack of cleanliness of bedding, water trough, and feed trough; nonevaluation of water hardness; lack of cleanliness of milk tank; and nonapplication of forestripping. After multivariate analysis, an association was observed with inadequate cleanliness of bedding and milk tank and the nonapplication of forestripping. PCR analysis of milk filters was a rapid and sensitive method for the microbiological evaluation of herd contamination status and should be included among the registration requirements for the authorization to produce and sell raw milk. Specific control actions must be incorporated into the farmer's daily practices to ensure the low-risk production of raw milk.

Seroprevalence of IgG antibodies against Anaplasma marginale in cattle from south Mozambique

The current study aimed to investigate the seroprevalence of IgG antibodies to Anaplasma marginale in cattle from Maputo, Gaza and Inhambane provinces, south Mozambique. A total of 809 serum samples from cattle were obtained and tested by indirect enzyme-linked immunosorbent assay (i-ELISA). The chi-square test at 5% significance was used to assess the association between seroprevalence and the variables gender, age and geographic origin of animals. The overall seropositivity was 76.5% (n = 619) and anti-A. marginale antibodies were detected in 89.1% (n = 156), 68.4% (n = 308) and 84.2% (n = 155) of the animals in the provinces of Maputo, Gaza and Inhambane, respectively. A significant association (p < 0.05) was found with the geographic origin of the animals, while sex had no significant relationship. The frequencies of seropositive in the age groups were 63.2% (n = 72), 80.0% (n = 92), 83.1% (n = 98) and 77.3% (n = 357) for animals <12; >12 and ≤24; >24 and ≤36; >36 months, respectively. These results indicate that in southern Mozambique there are areas of enzootic stability to A. marginale. Thus, epidemiological monitoring is required to monitor the immune status of animals in the region.

Pathogen prevalence in ticks collected from the vegetation and livestock in Nigeria

Ticks are important disease vectors that can cause considerable economic losses by affecting animal health and productivity, especially in tropical and subtropical regions. In this study, we investigated the prevalence and diversity of bacterial and protozoan tick-borne pathogens in ticks collected from the vegetation and cattle in Nigeria by PCR. The infection rates of questing ticks were 3.1% for Rickettsia species, 0.1% for Coxiella burnetii and 0.4% for Borrelia species. Other pathogens, such as Babesia, Theileria, Anaplasma, and Ehrlichia species, were not detected in ticks from the vegetation. Feeding ticks collected from cattle displayed infection rates of 12.5% for Rickettsia species, 14% for Coxiella burnetii, 5.9% for Anaplasma species, 5.1% for Ehrlichia species, and 2.9% for Theileria mutans. Babesia and Borrelia species were not detected in ticks collected from cattle. Mixed infections were found only in feeding ticks and mainly Rickettsia species and Coxiella burnetii were involved. The diversity of tick-borne pathogens in Nigeria was higher in feeding than in questing ticks, suggesting that cattle serve as reservoirs for at least some of the pathogens studied, in particular C. burnetii. The total estimated herd infection rates of 20.6% for a Rickettsia africae-like species, 27% for Coxiella burnetii, and 8.5% for Anaplasma marginale/centrale suggest that these pathogens may have considerable implications for human and animal health.

An overview of methods used to clarify pathogenesis mechanisms of Campylobacter jejuni

Thermotolerant campylobacters are the most frequent cause of bacterial infection of the lower intestine worldwide. The mechanism of pathogenesis of Campylobacter jejuni comprises four main stages: adhesion to intestinal cells, colonization of the digestive tract, invasion of targeted cells, and toxin production. In response to the high number of cases of human campylobacteriosis, various virulence study models are available according to the virulence stage being analyzed. The aim of this review is to compare the different study models used to look at human disease. Molecular biology tools used to identify genes or proteins involved in virulence mechanisms are also summarized. Despite high cost and limited availability, animal models are frequently used to study digestive disease, in particular to analyze the colonization stage. Eukaryotic cell cultures have been developed because of fewer restrictions on their use and the lower cost of these cultures compared with animal models, and this ex vivo approach makes it possible to mimic the bacterial cell-host interactions observed in natural disease cases. Models are complemented by molecular biology tools, especially mutagenesis and DNA microarray methods to identify putative virulence genes or proteins and permit their characterization. No current model seems to be ideal for studying the complete range of C. jejuni virulence. However, the models available deal with different aspects of the complex pathogenic mechanisms particular to this bacterium.

The natural history of Anaplasma marginale

The intracellular pathogen Anaplasma marginale (Rickettsiales: Anaplasmataceae), described by Sir Arnold Theiler in 1910, is endemic worldwide in tropical and subtropical areas. Infection of cattle with A. marginale causes bovine anaplasmosis, a mild to severe hemolytic disease that results in considerable economic loss to both dairy and beef industries. Transmission of A. marginale to cattle occurs biologically by ticks and mechanically by biting flies and by blood-contaminated fomites. Both male ticks and cattle hosts become persistently infected with A. marginale and serve as reservoirs of infection. While erythrocytes are the major site of infection in cattle, A. marginale undergoes a complex developmental cycle in ticks that begins by infection of gut cells, and transmission to susceptible hosts occurs from salivary glands during feeding. Major surface proteins (MSPs) play a crucial role in the interaction of A. marginale with host cells, and include adhesion proteins and MSPs from multigene families that undergo antigenic change and selection in cattle, thus contributing to maintenance of persistent infections. Many geographic strains of A. marginale have been identified worldwide, which vary in genotype, antigenic composition, morphology and infectivity for ticks. Isolates of A. marginale may be maintained by independent transmission events and a mechanism of infection/exclusion in cattle and ticks. The increasing numbers of A. marginale genotypes identified in some geographic regions most likely resulted from intensive cattle movement. However, concurrent A. marginale strain infections in cattle was reported, but these strains were more distantly related. Phylogenetic studies of selected geographic isolates of A. marginale, using msp4 and msp1alpha, provided information about the biogeography and evolution of A. marginale, and msp1alpha genotypes appear to have evolved under positive selection pressure. Live and killed vaccines have been used for control of anaplasmosis and both types of vaccines have advantages and disadvantages. Vaccines have effectively prevented clinical anaplasmosis in cattle but have failed to block A. marginale infection. Vaccines are needed that can prevent clinical disease and, simultaneously, prevent infection in cattle and ticks, thus eliminating these hosts as reservoirs of infection. Advances in genomics, proteomics, immunology and biochemical and molecular technologies during the last decade have been applied to research on A. marginale and related organisms, and the recent development of a cell culture system for A. marginale has provided a format for studying the pathogen/tick interface. Recent advancements and new research methodologies should provide additional opportunities for development of new strategies for control and prevention of bovine anaplasmosis.