Microglia produce the amyloidogenic ABri peptide in familial British dementia

Mutations in ITM2B cause familial British, Danish, Chinese and Korean dementias. In familial British dementia (FBD) a mutation in the stop codon of the ITM2B gene (also known as BRI2 ) causes a C-terminal cleavage fragment of the ITM2B/BRI2 protein to be extended by 11 amino acids. This fragment, termed amyloid-Bri (ABri), is highly insoluble and forms extracellular plaques in the brain. ABri plaques are accompanied by tau pathology, neuronal cell death and progressive dementia, with striking parallels to the aetiology and pathogenesis of Alzheimer's disease. The molecular mechanisms underpinning FBD are ill-defined. Using patient-derived induced pluripotent stem cells, we show that expression of ITM2B/BRI2 is 34-fold higher in microglia than neurons, and 15-fold higher in microglia compared with astrocytes. This cell-specific enrichment is supported by expression data from both mouse and human brain tissue. ITM2B/BRI2 protein levels are higher in iPSC-microglia compared with neurons and astrocytes. Consequently, the ABri peptide was detected in patient iPSC-derived microglial lysates and conditioned media but was undetectable in patient-derived neurons and control microglia. Pathological examination of post-mortem tissue support ABri expression in microglia that are in proximity to pre-amyloid deposits. Finally, gene co-expression analysis supports a role for ITM2B/BRI2 in disease-associated microglial responses. These data demonstrate that microglia are the major contributors to the production of amyloid forming peptides in FBD, potentially acting as instigators of neurodegeneration. Additionally, these data also suggest ITM2B/BRI2 may be part of a microglial response to disease, motivating further investigations of its role in microglial activation. This has implications for our understanding of the role of microglia and the innate immune response in the pathogenesis of FBD and other neurodegenerative dementias including Alzheimer's disease.

Whole genome analysis in APOE4 homozygotes identifies the DAB1-RELN pathway in Alzheimer's disease pathogenesis

The APOE-ε4 allele is known to predispose to amyloid deposition and consequently is strongly associated with Alzheimer's disease (AD) risk. There is debate as to whether the APOE gene accounts for all genetic variation of the APOE locus. Another question which remains is whether APOE-ε4 carriers have other genetic factors influencing the progression of amyloid positive individuals to AD. We conducted a genome-wide association study in a sample of 5,390 APOE-ε4 homozygous (ε4ε4) individuals (288 cases and 5102 controls) aged 65 or over in the UK Biobank. We found no significant associations of SNPs in the APOE locus with AD in the sample of ε4ε4 individuals. However, we identified a novel genome-wide significant locus associated to AD, mapping to DAB1 (rs112437613, OR = 2.28, CI = 1.73-3.01, p = 5.4 × 10^-9). This identification of DAB1 led us to investigate other components of the DAB1-RELN pathway for association. Analysis of the DAB1-RELN pathway indicated that the pathway itself was associated with AD, therefore suggesting an epistatic interaction between the APOE locus and the DAB1-RELN pathway.

A genetic link between risk for Alzheimer's disease and severe COVID-19 outcomes via the OAS1 gene

Recently, we reported oligoadenylate synthetase 1 (OAS1) contributed to the risk of Alzheimer's disease, by its enrichment in transcriptional networks expressed by microglia. However, the function of OAS1 within microglia was not known. Using genotyping from 1313 individuals with sporadic Alzheimer's disease and 1234 control individuals, we confirm the OAS1 variant, rs1131454, is associated with increased risk for Alzheimer's disease. The same OAS1 locus has been recently associated with severe coronavirus disease 2019 (COVID-19) outcomes, linking risk for both diseases. The single nucleotide polymorphisms rs1131454(A) and rs4766676(T) are associated with Alzheimer's disease, and rs10735079(A) and rs6489867(T) are associated with severe COVID-19, where the risk alleles are linked with decreased OAS1 expression. Analysing single-cell RNA-sequencing data of myeloid cells from Alzheimer's disease and COVID-19 patients, we identify co-expression networks containing interferon (IFN)-responsive genes, including OAS1, which are significantly upregulated with age and both diseases. In human induced pluripotent stem cell-derived microglia with lowered OAS1 expression, we show exaggerated production of TNF-α with IFN-γ stimulation, indicating OAS1 is required to limit the pro-inflammatory response of myeloid cells. Collectively, our data support a link between genetic risk for Alzheimer's disease and susceptibility to critical illness with COVID-19 centred on OAS1, a finding with potential implications for future treatments of Alzheimer's disease and COVID-19, and development of biomarkers to track disease progression.

Trem2 promotes anti-inflammatory responses in microglia and is suppressed under pro-inflammatory conditions

Genome-wide association studies have reported that, amongst other microglial genes, variants in TREM2 can profoundly increase the incidence of developing Alzheimer’s disease (AD). We have investigated the role of TREM2 in primary microglial cultures from wild type mice by using siRNA to decrease Trem2 expression, and in parallel from knock-in mice heterozygous or homozygous for the Trem2 R47H AD risk variant. The prevailing phenotype of Trem2 R47H knock-in mice was decreased expression levels of Trem2 in microglia, which resulted in decreased density of microglia in the hippocampus. Overall, primary microglia with reduced Trem2 expression, either by siRNA or from the R47H knock-in mice, displayed a similar phenotype. Comparison of the effects of decreased Trem2 expression under conditions of lipopolysaccharide (LPS) pro-inflammatory or IL-4 anti-inflammatory stimulation revealed the importance of Trem2 in driving a number of the genes up-regulated in the anti-inflammatory phenotype. RNA-seq analysis showed that IL-4 induced the expression of a program of genes including Arg1 and Ap1b1 in microglia, which showed an attenuated response to IL-4 when Trem2 expression was decreased. Genes showing a similar expression profile to Arg1 were enriched for STAT6 transcription factor recognition elements in their promoter, and Trem2 knockdown decreased levels of STAT6. LPS-induced pro-inflammatory stimulation suppressed Trem2 expression, thus preventing TREM2’s anti-inflammatory drive. Given that anti-inflammatory signaling is associated with tissue repair, understanding the signaling mechanisms downstream of Trem2 in coordinating the pro- and anti-inflammatory balance of microglia, particularly mediating effects of the IL-4-regulated anti-inflammatory pathway, has important implications for fighting neurodegenerative disease.

Knock-in models related to Alzheimer's disease: synaptic transmission, plaques and the role of microglia

Background

Microglia are active modulators of Alzheimer’s disease but their role in relation to amyloid plaques and synaptic changes due to rising amyloid beta is unclear. We add novel findings concerning these relationships and investigate which of our previously reported results from transgenic mice can be validated in knock-in mice, in which overexpression and other artefacts of transgenic technology are avoided.

Methods

App^NL-F and App^NL-G-F knock-in mice expressing humanised amyloid beta with mutations in App that cause familial Alzheimer’s disease were compared to wild type mice throughout life. In vitro approaches were used to understand microglial alterations at the genetic and protein levels and synaptic function and plasticity in CA1 hippocampal neurones, each in relationship to both age and stage of amyloid beta pathology. The contribution of microglia to neuronal function was further investigated by ablating microglia with CSF1R inhibitor PLX5622.

Results

Both App knock-in lines showed increased glutamate release probability prior to detection of plaques. Consistent with results in transgenic mice, this persisted throughout life in App^NL-F mice but was not evident in App^NL-G-F with sparse plaques. Unlike transgenic mice, loss of spontaneous excitatory activity only occurred at the latest stages, while no change could be detected in spontaneous inhibitory synaptic transmission or magnitude of long-term potentiation. Also, in contrast to transgenic mice, the microglial response in both App knock-in lines was delayed until a moderate plaque load developed. Surviving PLX5266-depleted microglia tended to be CD68-positive. Partial microglial ablation led to aged but not young wild type animals mimicking the increased glutamate release probability in App knock-ins and exacerbated the App knock-in phenotype. Complete ablation was less effective in altering synaptic function, while neither treatment altered plaque load.

Conclusions

Increased glutamate release probability is similar across knock-in and transgenic mouse models of Alzheimer’s disease, likely reflecting acute physiological effects of soluble amyloid beta. Microglia respond later to increased amyloid beta levels by proliferating and upregulating Cd68 and Trem2. Partial depletion of microglia suggests that, in wild type mice, alteration of surviving phagocytic microglia, rather than microglial loss, drives age-dependent effects on glutamate release that become exacerbated in Alzheimer’s disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-021-00457-0.

Prodromal neuroinflammatory, cholinergic and metabolite dysfunction detected by PET and MRS in the TgF344-AD transgenic rat model of AD: a collaborative multi-modal study

Mouse models of Alzheimer's disease (AD) are valuable but do not fully recapitulate human AD pathology, such as spontaneous Tau fibril accumulation and neuronal loss, necessitating the development of new AD models. The transgenic (TG) TgF344-AD rat has been reported to develop age-dependent AD features including neuronal loss and neurofibrillary tangles, despite only expressing APP and PSEN1 mutations, suggesting an improved modelling of AD hallmarks. Alterations in neuronal networks as well as learning performance and cognition tasks have been reported in this model, but none have combined a longitudinal, multimodal approach across multiple centres, which mimics the approaches commonly taken in clinical studies. We therefore aimed to further characterise the progression of AD-like pathology and cognition in the TgF344-AD rat from young-adults (6 months (m)) to mid- (12 m) and advanced-stage (18 m, 25 m) of the disease. Methods: TgF344-AD rats and wild-type (WT) littermates were imaged at 6 m, 12 m and 18 m with [¹⁸F]DPA-714 (TSPO, neuroinflammation), [¹⁸F]Florbetaben (Aβ) and [¹⁸F]ASEM (α7-nicotinic acetylcholine receptor) and with magnetic resonance spectroscopy (MRS) and with (S)-[¹⁸F]THK5117 (Tau) at 15 and 25 m. Behaviour tests were also performed at 6 m, 12 m and 18 m. Immunohistochemistry (CD11b, GFAP, Aβ, NeuN, NeuroChrom) and Tau (S)-[¹⁸F]THK5117 autoradiography, immunohistochemistry and Western blot were also performed. Results: [¹⁸F]DPA-714 positron emission tomography (PET) showed an increase in neuroinflammation in TG vs wildtype animals from 12 m in the hippocampus (+11%), and at the advanced-stage AD in the hippocampus (+12%), the thalamus (+11%) and frontal cortex (+14%). This finding coincided with strong increases in brain microgliosis (CD11b) and astrogliosis (GFAP) at these time-points as assessed by immunohistochemistry. In vivo [¹⁸F]ASEM PET revealed an age-dependent increase uptake in the striatum and pallidum/nucleus basalis of Meynert in WT only, similar to that observed with this tracer in humans, resulting in TG being significantly lower than WT by 18 m. In vivo [¹⁸F]Florbetaben PET scanning detected Aβ accumulation at 18 m, and (S)-[¹⁸F]THK5117 PET revealed subsequent Tau accumulation at 25m in hippocampal and cortical regions. Aβ plaques were low but detectable by immunohistochemistry from 6 m, increasing further at 12 and 18 m with Tau-positive neurons adjacent to Aβ plaques at 18 m. NeuroChrom (a pan neuronal marker) immunohistochemistry revealed a loss of neuronal staining at the Aβ plaques locations, while NeuN labelling revealed an age-dependent decrease in hippocampal neuron number in both genotypes. Behavioural assessment using the novel object recognition task revealed that both WT & TgF344-AD animals discriminated the novel from familiar object at 3 m and 6 m of age. However, low levels of exploration observed in both genotypes at later time-points resulted in neither genotype successfully completing the task. Deficits in social interaction were only observed at 3 m in the TgF344-AD animals. By in vivo MRS, we showed a decrease in neuronal marker N-acetyl-aspartate in the hippocampus at 18 m (-18% vs age-matched WT, and -31% vs 6 m TG) and increased Taurine in the cortex of TG (+35% vs age-matched WT, and +55% vs 6 m TG). Conclusions: This multi-centre multi-modal study demonstrates, for the first time, alterations in brain metabolites, cholinergic receptors and neuroinflammation in vivo in this model, validated by robust ex vivo approaches. Our data confirm that, unlike mouse models, the TgF344-AD express Tau pathology that can be detected via PET, albeit later than by ex vivo techniques, and is a useful model to assess and longitudinally monitor early neurotransmission dysfunction and neuroinflammation in AD.

Prevalence of ticks (Acari: Ixodidae) and Theileria annulata infection of cattle in Gezira State, Sudan

This study was conducted in Gezira State, central Sudan during January, May and August 2014 to determine species of ticks infesting cattle and prevalence of Theileria annulata infection and antibodies. A total of 200 head of cattle were sampled for ticks, blood smears, lymph node biopsy smears and sera from five study areas. Zebu (Butana and Kenana) and cross-bred (Zebu X Friesian) cattle of both sexes were sampled. Cattle age groups were younger than one year, one year to younger than four years and four years and older. Coat colour of cattle was recorded. The results revealed that cattle were infested with Rhipicephalus evertsi evertsi (n = 562, 51.6%), Hyalomma anatolicum (n = 289, 26.5%), H. rufipes (n = 70, 6.4%), R. sanguineus sanguineus (n = 59, 5.4%), R. decoloratus (n = 39, 3.6%), Amblyomma lepidum (n = 35, 3.2%), H. impeltatum (n = 26, 2.4%) and H. dromedarii (n = 9, 0.8%). Out of 200 blood and biopsy smears, 33 (16.5%) showed piroplasms for Theileria spp., while 29 (14.5%) were positive for Theileria spp. schizonts. Seropositivity for T. annulata using indirect fluorescent antibody (IFA) test was 94 (47%). It is concluded that there are three genera of hard ticks and eight species in Gezira State and tropical theileriosis is endemic in the state. These findings are the first records in Gezira State, Central Sudan and it is highly recommended to consider the endemicity of tropical theileriosis particularly in cattle upgrading programmes.

Genetic variability in response to amyloid beta deposition influences Alzheimer's disease risk

Genome-wide association studies of late-onset Alzheimer's disease risk have previously identified genes primarily expressed in microglia that form a transcriptional network. Using transgenic mouse models of amyloid deposition, we previously showed that many of the mouse orthologues of these risk genes are co-expressed and associated with amyloid pathology. In this new study, we generate an improved RNA-seq-derived network that is expressed in amyloid-responsive mouse microglia and we statistically compare this with gene-level variation in previous human Alzheimer's disease genome-wide association studies to predict at least four new risk genes for the disease (OAS1, LAPTM5, ITGAM/CD11b and LILRB4). Of the mouse orthologues of these genes Oas1a is likely to respond directly to amyloid at the transcriptional level, similarly to established risk gene Trem2, because the increase in Oas1a and Trem2 transcripts in response to amyloid deposition in transgenic mice is significantly higher than both the increase of the average microglial transcript and the increase in microglial number. In contrast, the mouse orthologues of LAPTM5, ITGAM/CD11b and LILRB4 (Laptm5, Itgam/CD11b and Lilra5) show increased transcripts in the presence of amyloid plaques similar in magnitude to the increase of the average microglial transcript and the increase in microglia number, except that Laptm5 and Lilra5 transcripts increase significantly quicker than the average microglial transcript as the plaque load becomes dense. This work suggests that genetic variability in the microglial response to amyloid deposition is a major determinant for Alzheimer's disease risk, and identification of these genes may help to predict the risk of developing Alzheimer's disease. These findings also provide further insights into the mechanisms underlying Alzheimer's disease for potential drug discovery.

Improving Mouse Models for Dementia. Are All the Effects in Tau Mouse Models Due to Overexpression?

Mouse models of Alzheimer's disease have commonly used transgenic overexpression of genes involved in production of amyloid β (APP and/or PSEN1/2) or Tau (MAPT) with mutations that result in familial forms of dementia. We discuss possible improvements that may create full models while avoiding the problems of overexpression and report synaptic results in APPKI models. We stress use of inappropriate controls without overexpression of the normal human protein and the mismatch between the learning deficits reported in mice with plaques but no tangles and the human condition. We focus on Tau overexpression, including new data that support previous reports of the grossly nonlinear relationship between Tau overexpression and neurofibrillary tangle load, with a twofold increase in Tau protein, resulting in a 100-fold increase in tangle density. These data also support the hypothesis that a high concentration of soluble Tau, in overexpression models, plays an important direct role in neurodegeneration, rather than only via aggregation. Finally, we hypothesize that there is an optimal concentration range over which Tau can bind to microtubules and a threshold beyond which much of the overexpressed protein is unable to bind. The excess thus causes toxicity in ways not necessarily related to the process in human dementias.

Effects of rising amyloidβ levels on hippocampal synaptic transmission, microglial response and cognition in APPSwe/PSEN1M146V transgenic mice

BACKGROUND

Progression of Alzheimer's disease is thought initially to depend on rising amyloidβ and its synaptic interactions. Transgenic mice (TASTPM; APPSwe/PSEN1M146V) show altered synaptic transmission, compatible with increased physiological function of amyloidβ, before plaques are detected. Recently, the importance of microglia has become apparent in the human disease. Similarly, TASTPM show a close association of plaque load with upregulated microglial genes.

METHODS

CA1 synaptic transmission and plasticity were investigated using in vitro electrophysiology. Microglial relationship to plaques was examined with immunohistochemistry. Behaviour was assessed with a forced-alternation T-maze, open field, light/dark box and elevated plus maze.

FINDINGS

The most striking finding is the increase in microglial numbers in TASTPM, which, like synaptic changes, begins before plaques are detected. Further increases and a reactive phenotype occur later, concurrent with development of larger plaques. Long-term potentiation is initially enhanced at pre-plaque stages but decrements with the initial appearance of plaques. Finally, despite altered plasticity, TASTPM have little cognitive deficit, even with a heavy plaque load, although they show altered non-cognitive behaviours.

INTERPRETATION

The pre-plaque synaptic changes and microglial proliferation are presumably related to low, non-toxic amyloidβ levels in the general neuropil and not directly associated with plaques. However, as plaques grow, microglia proliferate further, clustering around plaques and becoming phagocytic. Like in humans, even when plaque load is heavy, without development of neurofibrillary tangles and neurodegeneration, these alterations do not result in cognitive deficits. Behaviours are seen that could be consistent with pre-diagnosis changes in the human condition.

FUNDING

GlaxoSmithKline; BBSRC; UCL; ARUK; MRC.

Molecular, serological and parasitological survey of Theileria annulata in North Kordofan State, Sudan

This survey was conducted to detect Theileria annulata infection in indigenous (Zebu) and cross (indigenous × Friesian) cattle (n 604) of different sex & age groups, and to investigate prevalence of ticks infesting cattle in North Kordofan State, Sudan. Ticks, blood smears, serum samples and blood spots on filter paper were collected from four municipalities at four monthly intervals during the period from August 2008 to July 2009. Out of 604 blood smears, 69 (11.4%, 95% CI: 16.9-5.9) were positive for Theileria piroplasms; whereas, out of 240 serum samples, 164 (68.3%, 95% CI: 89.3-47.3) were positive for antibodies against T. annulata using IFA test. Using PCR, out of 100 blood spots on filter paper, 8 (8%, 95% CI: 9.6-6.4) revealed T. annulata DNA. The highest prevalence of Theileria spp. piroplasms and T. annulata antibodies was recorded in August (15.9 ± 4.6) followed by February (13.3 ± 3.8) and the lowest was in May (3.9 ± 1.0). Among cattle breeds, the highest prevalence of piroplasms (11.9 ± 5.0) and T. annulata antibodies (68.9 ± 10) was among zebu cattle. PCR assays revealed the highest prevalence rate of T. annulata DNA in February (12.5 ± 1.4) followed by August (6.1 ± 0.7) and the lowest was in May (5.7 ± 0.7). According to cattle breeds, T. annulata DNA was detected in cross-bred cattle (3.3 ± 0.4) more than zebu cattle (10 ± 1.6). Seven tick species belonging to four genera and were identified, Amblyomma lepidum, Hyalomma dromedarii, H. impeltatum, H. rufipes, Rhipicephalus evertsi evertsi, Rhipicephalus decoloratus, R. annulatus. The most abundant tick species was H. rufipes followed by H. impeltatum, R. e. evertsi, H. dromedarii, R. decoloratus, A. lepidum and R. annulatus. Theileria annulata has been detected for the first time in North Kordofan State, though at a low prevalence rate. This finding is an alarming situation since tropical theileriosis is an emerging disease and it is widely believed that this economically important tick-borne parasite does not exist in this state. The possible alternative vector(s) of T. annulata in the absence of the known vector H. anatolicum is discussed.

First effects of rising amyloid-β in transgenic mouse brain: synaptic transmission and gene expression

Understanding the earliest changes in Alzheimer’s disease may help in the prevention of cognitive impairment. In a transgenic mouse model, Cummings et al. show that synaptic changes occur shortly after soluble amyloid-β levels become measurable, and before the rapid increases in total Aβ and Aβ₄₂:Aβ₄₀ that lead to detectable plaque deposition.

Detecting and treating Alzheimer’s disease, before cognitive deficits occur, has become the health challenge of our time. The earliest known event in Alzheimer’s disease is rising amyloid-β. Previous studies have suggested that effects on synaptic transmission may precede plaque deposition. Here we report how relative levels of different soluble amyloid-β peptides in hippocampus, preceding plaque deposition, relate to synaptic and genomic changes. Immunoprecipitation-mass spectrometry was used to measure the early rise of different amyloid-β peptides in a mouse model of increasing amyloid-β (‘TASTPM’, transgenic for familial Alzheimer’s disease genes APP/PSEN1). In the third postnatal week, several amyloid-β peptides were above the limit of detection, including amyloid-β₄₀, amyloid-β₃₈ and amyloid-β₄₂ with an intensity ratio of 6:3:2, respectively. By 2 months amyloid-β levels had only increased by 50% and although the ratio of the different peptides remained constant, the first changes in synaptic currents, compared to wild-type mice could be detected with patch-clamp recordings. Between 2 and 4 months old, levels of amyloid-β₄₀ rose by ∼7-fold, but amyloid-β₄₂ rose by 25-fold, increasing the amyloid-β₄₂:amyloid-β₄₀ ratio to 1:1. Only at 4 months did plaque deposition become detectable and only in some mice; however, synaptic changes were evident in all hippocampal fields. These changes included increased glutamate release probability (P < 0.001, n = 7–9; consistent with the proposed physiological effect of amyloid-β) and loss of spontaneous action potential-mediated activity in the cornu ammonis 1 (CA1) and dentate gyrus regions of the hippocampus (P < 0.001, n = 7). Hence synaptic changes occur when the amyloid-β levels and amyloid-β₄₂:amyloid-β₄₀ ratio are still low compared to those necessary for plaque deposition. Genome-wide microarray analysis revealed changes in gene expression at 2–4 months including synaptic genes being strongly affected but often showing significant changes only by 4 months. We thus demonstrate that, in a mouse model of rising amyloid-β, the initial deposition of plaques does not occur until several months after the first amyloid-β becomes detectable but coincides with a rapid acceleration in the rise of amyloid-β levels and the amyloid-β₄₂:amyloid-β₄₀ ratio. Prior to acceleration, however, there is already a pronounced synaptic dysfunction, reflected as changes in synaptic transmission and altered gene expression, indicating that restoring synaptic function early in the disease progression may represent the earliest possible target for intervention in the onset of Alzheimer’s disease.

A genome-wide gene-expression analysis and database in transgenic mice during development of amyloid or tau pathology

We provide microarray data comparing genome-wide differential expression and pathology throughout life in four lines of "amyloid" transgenic mice (mutant human APP, PSEN1, or APP/PSEN1) and "TAU" transgenic mice (mutant human MAPT gene). Microarray data were validated by qPCR and by comparison to human studies, including genome-wide association study (GWAS) hits. Immune gene expression correlated tightly with plaques whereas synaptic genes correlated negatively with neurofibrillary tangles. Network analysis of immune gene modules revealed six hub genes in hippocampus of amyloid mice, four in common with cortex. The hippocampal network in TAU mice was similar except that Trem2 had hub status only in amyloid mice. The cortical network of TAU mice was entirely different with more hub genes and few in common with the other networks, suggesting reasons for specificity of cortical dysfunction in FTDP17. This Resource opens up many areas for investigation. All data are available and searchable at http://www.mouseac.org.

Naturally occurring infections of cattle with Theileria lestoquardi and sheep with Theileria annulata in the Sudan

Theileria annulata is endemic in northern Sudan, hindering all efforts at upgrading cattle for milk production. T. lestoquardi clinical cases occur throughout the year and causes annual outbreaks that result in substantial losses in sheep. In the northern Sudan both cattle and small ruminants are frequently raised together and/or share common grazing grounds at river banks. In an attempt to evaluate field cross infectivity of Theileria lestoquardi and T. annulata in cattle and sheep respectively, a PCR analysis was carried out on samples collected from closely reared sheep and cattle using both T. annulata and T. lestoquardi specific primers. A total of 19 sheep out of 51 (37.3%) were positive for T. lestoquardi while four sheep (7.8%) showed T. annulata specific amplicons. A total of 38 out of 52 (73.1%) surveyed cattle were PCR positive for T. annulata and only two (3.8%) showed T. lestoquardi specific bands. These findings indicate complex epidemiology of both infections in areas where both parasites are transmitted by the same vector and call for further investigations of this phenomenon.

A FOXO-Pak1 transcriptional pathway controls neuronal polarity

Neuronal polarity is essential for normal brain development and function. However, cell-intrinsic mechanisms that govern the establishment of neuronal polarity remain to be identified. Here, we report that knockdown of endogenous FOXO proteins in hippocampal and cerebellar granule neurons, including in the rat cerebellar cortex in vivo, reveals a requirement for the FOXO transcription factors in the establishment of neuronal polarity. The FOXO transcription factors, including the brain-enriched protein FOXO6, play a critical role in axo-dendritic polarization of undifferentiated neurites, and hence in a switch from unpolarized to polarized neuronal morphology. We also identify the gene encoding the protein kinase Pak1, which acts locally in neuronal processes to induce polarity, as a critical direct target gene of the FOXO transcription factors. Knockdown of endogenous Pak1 phenocopies the effect of FOXO knockdown on neuronal polarity. Importantly, exogenous expression of Pak1 in the background of FOXO knockdown in both primary neurons and postnatal rat pups in vivo restores the polarized morphology of neurons. These findings define the FOXO proteins and Pak1 as components of a cell-intrinsic transcriptional pathway that orchestrates neuronal polarity, thus identifying a novel function for the FOXO transcription factors in a unique aspect of neural development.

Seroprevalence of tick-borne diseases among cattle in the Sudan

This study was carried out to determine the prevalence of Theileria annulata, Theileria mutans, Babesia bigemina, and Anaplasma marginale antibodies among cattle in the Sudan. A total of 600 serum samples were collected from indigenous (zebu) and crossbred cattle (zebu x Friesian) of both sex and different age groups. Indirect enzyme-linked immunosorbent assay was used to assess antibodies against tick-borne diseases in apparently healthy cattle. The overall prevalence rates of T. annulata, T. mutans, B. bigemina, and A. marginale antibodies were found to be 30.8%, 6.1%, 10.7%, and 38.9%, respectively. The highest seroprevalence of T. annulata was reported in Atbara and El Damer, Northern Sudan. There were no significant associations for the seroprevalence of all tick-borne diseases reported among different age groups. Although there were no significant differences between the two breeds of cattle examined for T. annulata, T. mutans, and B. bigemina antibodies, there was a significant difference for prevalence of antibodies against A. marginale, with highest percentages of antibodies in indigenous cattle. Six different combinations of mixed infection were detected. This is the first report in which antibodies against A. marginale among cattle in Northern Sudan is reported. The findings imply that antibodies to tick-borne infections are widely distributed in the region. The need for further investigations using more advanced techniques is recommended.

Development and evaluation of a loop-mediated isothermal amplification method for diagnosis of tropical theileriosis

A loop-mediated isothermal amplification (LAMP) assay was developed and evaluated for diagnosis of tropical theileriosis. A set of six primers was designed based on the unique gene of Theileria annulata (Theileria annulata strain Ankara hypothetical protein (GeneDB TA04795). The protocol for the reaction was setup and the specificity and sensitivity of the assay were established. The specificity experiment showed that LAMP primers amplified T. annulata DNA successfully, while no amplification was seen for Theileria parva, Theileria mutans, Theileria sergenti, Theileria sinensis, Babesia bovis as well as bovine genomic DNA and water control. When the sensitivity of LAMP assay was compared with that of conventional PCR a 10-fold higher sensitivity was found, with a detection limit of 10 pg/microl of genomic DNA isolated from a T. annulata-infected cell line. The LAMP product was confirmed by restriction digestion and staining with SYBR Green I. Furthermore, the LAMP assay was applied for the diagnosis of T. annulata in field samples and compared with reverse line blot (RLB), demonstrating that results of the LAMP assay corresponded to those of RLB. These results indicate that the LAMP assay is rapid and simple to run, cost-effective, sensitive and specific and has potential usefulness for application in epidemiological studies on T. annulata infection of cattle.

Reliminary survey of ticks (Acari: Ixodidae) on cattle in Central Equatoria State, Southern Sudan

In a preliminary survey conducted in 2005, the species composition and seasonality of ticks infesting cattle in Central Equatoria State, Southern Sudan was determined. Three locations were selected (Gumbo, Khor Rumla and Nyaing) and surveyed every 3 months. Two cattle herds in each of the three locations were visited four times during the study period. Total body collections of ticks were made from each of five cattle (Nilotic Zebu breed) kept in six different herds. Four tick genera and ten species were identified. The tick species identified were Amblyomma lepidum, Amblyomma variegatum, Boophilus annulatus, Boophilus decoloratus, Hyalomma marginatum rufipes, Hyalomma truncatum, Rhipicephalus appendiculatus, Rhipicephalus evertsi evertsi, Rhipicephalus praetextatus and Rhipicephalus sanguineus group. The highest number of ticks was collected in October during the rainy season. A finding of great significance was that R. appendiculatus, vector of East Coast fever, has now firmly established itself throughout the year with possible implications for cattle production in Central Equatoria State.

Comparisons among two serological tests and microscopic examination for the detection of Theileria annulata in cattle in northern Sudan

We tested the agreement between microscopic examination (ME), a surface protein-detecting enzyme-linked immunosorbent assay (TaSP ELISA) and an indirect fluorescent assay (IFA) for detection of Theileria annulata in 2,661 naturally infected cattle from northern Sudan (samples collected between June 2001 and July 2002). In the ME, we detected piroplasms in 364/2,661 cattle (14%), and the kappas between the ME and the serological tests were poor (TaSP ELISA 10%; IFA 8%). The TaSP ELISA detected 885/2,661 cattle as positive, and the Rogan-and-Gladen corrected true prevalence of this sample was estimated to be 30%. The relative sensitivity and specificity of the IFA (compared to the previously validated TaSP ELISA) were 70.7% and 81.8%, respectively.

Determination of potential risk factors associated with Theileria annulata and Theileria parva infections of cattle in the Sudan

A multi-variate logistic regression analysis was performed on two sets of data on the prevalence of Theileria annulata in Northern Sudan and Theileria parva in Southern Sudan, to determine the potential risk factors that might affect the distribution of the infections in those regions. The logistic regression model was fit with the tested risk factors for each disease, separately. The results indicated that locations, management systems and age could be held as risk factors for T. annulata infection in Northern Sudan, while for T. parva locations and seasons could be held as risk factors in Southern Sudan. The results of this study will assist in the development of more effective control strategies for smallholder dairy farms in the country.

Epidemiological studies on tick-borne diseases of cattle in Central Equatoria State, Southern Sudan

A herd-based study was carried out in Central Equatoria State, Southern Sudan, to study epidemiological aspects of tick-borne diseases. Six herds of cattle situated in three different locations were selected and investigated every 3 months during the year 2005. Blood smears for Giemsa staining and blood spots on filter paper for deoxyribonucleic acid extraction were collected from 600 apparently healthy indigenous cattle. A total of 69 (11.5%) samples showed the presence of piroplasms in Giemsa-stained blood smears, and polymerase chain reaction increased the detection limit to 297 (49.5%). Using reverse line blot, it was possible to detect and differentiate eight different piroplasms namely, Theileria parva (71.2%), Theileria mutans (73%), Theileria velifera (45.3%), Theileria taurotragi (2.7%), Theileria buffeli (0.5%), Theileria annulata (0.2%), Babesia bovis (1.7%), and Babesia bigemina (0.3%). Mixed infections were detected in 406 samples (67.7%) accounting for 17 different combinations. High infection of Theileria parva was reported among young calves compared to older cattle. The highest prevalence of Theileria parva was reported in the rainy season (October). The implications of these results on the epidemiology of tick-borne diseases are discussed with emphasis on East Coast fever.

Natural infection rates and transmission of Theileria annulata by Hyalomma anatolicum anatolicum ticks in the Sudan

Hyalomma anatolicum anatolicum nymphs were collected from two localities in the Sudan: Eddamer in Northern Sudan and Wad-Medani in Central Sudan. They were allowed to moult to adult ticks, which were assessed for Theileria infection in their salivary glands using Feulgen stain. At Eddamer, 49.6% of 123 ticks examined were infected with Theileria and the mean intensity of infection was 1.3 (i.e. the number of infected acini/number of infected ticks). At Wad-Medani, 8.6% of 162 ticks were infected and the mean intensity of infection was 7.9. The prevalence of infection was higher in female than in male ticks at both localities. When adult H. a. anatolicum were applied onto two susceptible calves, both animals developed the severe form of theileriosis.

Preliminary survey of ticks (Acari: Ixodidae) on cattle in northern Sudan

In a cross sectional survey conducted during the period June 2001 to July 2002, the geographical distribution of ticks on cattle in the Sudan was determined. Seventeen locations were surveyed from Northern, Central, Eastern, Western, Blue Nile and White Nile Provinces. Total body collections of ticks were made from 20 cattle at each location. Four tick genera and 11 species were identified. The tick species collected included Amblyomma lepidum, Amblyomma variegatum, Boophilus decoloratus, Hyalomma anatolicum anatolicum, Hyalomma dromedarii, Hyalomma impeltatum, Hyalomma marginatum rufipes, Hyalomma truncatum, Rhipicephalus evertsi evertsi, Rhipicephalus sanguineus group and Rhipicephalus simus simus. Major ecological changes have occurred due to extensive animal movement, deforestation, desertification and establishment of large mechanized agricultural schemes. These factors have certainly affected the distribution of ticks and tick-borne diseases in the Sudan. The absence of A. variegatum and A. lepidum in northern Sudan was not surprising, since these tick species are known to survive in humid areas and not in the desert and semi-desert areas of northern Sudan. The absence of B. annulatus in northern and central Sudan is in accordance with the finding that this tick species is restricted to the southern parts of the central Sudan. The presence of H. anatolicum anatolicum in Um Benin in relatively high abundance is an interesting finding. The present finding may indicate that the southern limit of this species has changed and moved southwards to latitude 13 degrees N. It is concluded that major changes in tick distribution have taken place in the Sudan.

Application of the recombinant Theileria annulata surface protein in an indirect ELISA for the diagnosis of tropical theileriosis

The recombinant surface protein of Theileria annulata (TaSP) was used in the standardization and validation of an enzyme linked immunosorbent assay (ELISA) for the detection of circulating antibodies against tropical theileriosis. ELISA data were expressed as the percentage positivity (PP) of the reactivity of an internal positive control. A total of 50 sera samples from a disease-free area were used for the calculation of the cut-off value which served as a threshold between the positive and the negative sera samples. This was determined as the mean PP plus two standard deviations or the twice the mean PP of the results obtained with these negative samples. The obtained thresholds were 17.8% and 18.3%, respectively. Accordingly, the reactivity of 140 field sera samples collected at random from an area known to be endemic for tropical theileriosis in Sudan was determined as PP values which were then compared to the results obtained using the indirect fluorescence antibody test (IFAT) from the same samples. Both tests showed a high degree of correlation. The TaSP-ELISA had a sensitivity of 99.1% and specificity of 90.47% when taking the IFAT as a reference test. Our test has proved its suitability for the diagnosis of tropical theileriosis and could be used in serological surveys to map out the prevalence of the disease or to monitor vaccination efficiencies in disease-free populations.

Survey of Theileria lestoquardi antibodies among Sudanese sheep

The prevalence of Theileria lestoquardi antibodies in Sudanese sheep from nine geographical areas in Sudan was determined using indirect fluorescent antibody "IFA" test. Out of 315 samples examined, 51 (16.2%) were found positive and ranged between 23.4% in River Nile State and 10% in Kasala and Darfour Provinces with an overall prevalence of 16.2% indicating widespread distribution of the infection. We also report on presence of antibodies reactive to Theileria annulata in sheep sera.