Integrated control of vector-borne diseases of livestock--pyrethroids: panacea or poison?

Tick- and tsetse-borne diseases cost Africa approximately US$4-5 billion per year in livestock production-associated losses. The use of pyrethroid-treated cattle to control ticks and tsetse promises to be an increasingly important tool to counter this loss. However, uncontrolled use of this technology might lead to environmental damage, acaricide resistance in tick populations and a possible exacerbation of tick-borne diseases. Recent research to identify, quantify and to develop strategies to avoid these effects are highlighted

Cross-sectional study of Fasciola gigantica and other trematode infections of cattle in Edu Local Government Area, Kwara State, North-central Nigeria

BACKGROUND: Trematode infections of livestock are of global veterinary and public health importance causing serious economic losses. Majority of data on burden of trematode infections in Nigeria are based on abattoir surveys and there are very few data on herd level risk factors. The present study investigated the prevalence of, and herd level risk factors for, fasciolosis and other trematode infections in cattle in Edu Local Government Area (LGA). METHODS: A cross-sectional survey used two-stage study design to investigate cattle belonging to 65 households. Two questionnaires were administered for household-level and individual cattle-level data. Faecal and blood samples were obtained from the cattle. Logistic regression analyses were performed to determine risk factors for infections. RESULTS: Of 686 faecal samples analysed, 74.9 %, 16.1 %, 7.3 % and 1.2 % were positive for infections with Fasciola gigantica, paramphistomes, Dicrocoelium hospes and Schistosoma bovis respectively. Fasciola gigantica had higher prevalence in adult cattle (77.3 %) than weaners (62.5 %). Majority of co-infections was a combination of F. gigantica with paramphistomes 84/130 (64.6 %). Most (58.9 %) of the cattle belonged to FAMACHA© score 2. The mean packed cell volume (PCV) was 34.4 %. The sensitivity and specificity of FAMACHA© for anaemia (PCV < 24 %) were 18.2 and 96.9 %, respectively. Positive correlation was obtained between faecal egg counts for F. gigantica and paramphistomes (R = 0.15, P = 0.0001). Adult cattle were more likely to be infected with F. gigantica (odds ratio, OR: 1.94; Confidence Interval, CI: 1.19–3.16) than weaners. Cattle belonging to household heads aged between 40–59 years were more likely infected with paramphistomes (OR: 1.95; CI: 1.02–3.74) than those belonging to other age groups. Cattles from herds with size ≥ 100 were more likely infected with D. hospes than those from smaller herds (OR: 6.98; CI: 2.94–16.6). CONCLUSION: This study revealed high prevalence of infection with F. gigantica in Kwara State. The co-infections by F. gigantica and paramphistomes with a positive correlation should be considered during anthelmintic therapy. There is a need to optimise and validate the FAMACHA© for use in cattle based on breeds and variation in colour of ocular mucous membrane. Risk factors identified could assist in tailoring control strategies for various trematode infections to particular groups of farmers and cattle. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13071-016-1737-5) contains supplementary material, which is available to authorized users

Development and Application of ELISAs to Improve the Chemoprophylactic Control of African Bovine Trypanosomiasis

The control of bovine trypanosomiasis in Africa continues to rely heavily on the chemoprophylactic drug isometamidium chloride (SamorinRTM). However, despite many years of use, no methods are available which are sufficiently sensitive to measure drug levels in treated cattle. Two new enzyme-linked immunosorbent assay (ELISA) procedures for the detection and quantification of isometamidium in bovine serum were developed and validated. The first of these, an indirect competition ELISA (ICE) was capable of detecting isometamidium to approximately 0.1 ngml-1. Following the treatment of cattle with isometamidium chloride by intramuscular injection at the recommended prophylactic dose rate of 1.0 mgkg-1, the drug could be detected in serum samples for up to four months. In a controlled laboratory experiment, Boran cattle injected intramuscularly with isometamidium chloride (dose 1.0 mgkg-1 body weight) were challenged at monthly intervals with Glossina morsitans centralis infected with one of three populations of T. congolense (IL 3893, IL 3889 or IL 1180) until all animals became infected. Untreated control cattle confirmed the infectivity of challenge. All cattle challenged with IL 3893 or IL 3889 developed infection following the first challenge, at which time the mean serum drug concentration was 6 ngml-1. Cattle challenged with IL 1180 became infected following 6 to 8 challenges. The mean serum drug concentration in these cattle at the time of their third challenge with IL 1180 was 0.75 ngml-1. Trypanosome populations IL 3893 and IL 3889 were considered to be highly resistant to isometamidium, while IL 1180, relatively sensitive. Hence, T. congolense persisting at serum isometamidium concentrations greater than 0.75 ngml-1 can be considered moderately resistant, and at concentrations greater than 6 ngml-1 markedly resistant. In a second, similar experiment isometamidium treated (1.0 mgkg-1) Boran cattle were with challenged monthly with T. congolense IL 1180 or a moderately isometamidium resistant T. congolense clone (IL 3343). The distribution of trypanosome challenge over a number of three month prophylactic periods was uneven, and almost ail challenge (based on the infection rate in untreated control cattle) occurred at the end of such periods. At the time of challenge, concentrations in the treated group were at their lowest and no inferences could be made about drug resistance in trypanosome infections, all of which were caused by T. vivax. A simpler, competitive enzyme immunoassay (CEIA) developed for isometamidium in bovine serum has several advantages over the ICE; fewer incubation steps; frozen storage of microtitre plates in batches; overnight competition incubation. The response variance of 57 untreated cattle was small (CV approximately 10%); partitioning showed 77% of this variance to be intrinsic to the samples, and 23% due to procedure (CV of duplicates wells approximately 5%). The CEIA could detect isometamidium in serum of treated cattle for up to ten weeks following treatment, with a high level of reproducibility. The limit of detection is approximately 0.5 ngml-1. The CEIA was used to investigate the pharmacokinetics of isometamidium in Friesian cattle (Bos taurus) treated intravenously and intramuscularly (dose rate 1.0 mgkg-1 body weight). The major pharmacokinetic parameters were calculated using standard pharmacokinetic equations. The large VSS (mean 24 lkg-1), and the prolonged MRT (83 h) and terminal phase half-life (136 h) following intravenous injection were consistent with extensive uptake of the drug into tissues such as liver, kidney and spleen. The relatively low bioavailability (60%), and prolonged MAT (7.8 days) following intramuscular injection was consistent with a primary depot at the site of injection. Isometamidium could be detected using the CEIA in the sera of all but one of 24 cattle treated intramuscularly (1.0 mgkg-1 body weight) in an area of natural tsetse challenge. Treated cattle were protected against trypanosome infections for at least 18 weeks; thereafter three trypanosome infections were detected, between 20 and 22 weeks following treatment. In contrast, in 18 untreated control cattle, nine trypanosome infections were detected over the first 18 weeks. While there was no evidence of drug-resistant trypanosomes, the CEIA was capable of quantifying drug-levels in 20 out of 23 cattle for at least 70 days. Finally, the CEIA was used to investigate the role of isometamidium in an experimentally induced wasting syndrome in Maasai Zebu cattle under a regimen of frequently repeated isometamidium treatments. Significant weight loss and mortality occurred in poorly nourished cattle after three or four isometamidium treatments and additional treatments with diminazene. Weight losses and glutamate dehydrogenase levels were correlated with isometamidium concentrations which showed small but significant elevations with successive treatments, but no marked increases. Such frequently repeated treatment regimens must be considered inadvisable. In conclusion, the two ELISAs are capable of determining isometamidium concentrations in sera from cattle in the field, and promise to provide a practical means of rationalising chemoprophylactic drug regimens, particularly where they can assist in identifying the development of trypanocidal drug resistance

Diagnosis of cattle diseases endemic to sub-Saharan Africa : evaluating a low cost decision support tool in use by veterinary personnel

Background: Diagnosis is key to control and prevention of livestock diseases. In areas of sub-Saharan Africa where private practitioners rarely replace Government veterinary services reduced in effectiveness by structural adjustment programmes, those who remain lack resources for diagnosis and might benefit from decision support. Methodology/Principal Findings: We evaluated whether a low-cost diagnostic decision support tool would lead to changes in clinical diagnostic practice by fifteen veterinary and animal health officers undertaking primary animal healthcare in Uganda. The eight diseases covered by the tool included 98% of all bovine diagnoses made before or after its introduction. It may therefore inform proportional morbidity in the area; breed, age and geographic location effects were consistent with current epidemiological understanding. Trypanosomosis, theileriosis, anaplasmosis, and parasitic gastroenteritis were the most common conditions among 713 bovine clinical cases diagnosed prior to introduction of the tool. Thereafter, in 747 bovine clinical cases estimated proportional morbidity of fasciolosis doubled, while theileriosis and parasitic gastroenteritis were diagnosed less commonly and the average number of clinical signs increased from 3.5 to 4.9 per case, with 28% of cases reporting six or more signs compared to 3% beforehand. Anaemia/pallor, weakness and staring coat contributed most to this increase, approximately doubling in number and were recorded in over half of all cases. Finally, although lack of a gold standard hindered objective assessment of whether the tool improved the reliability of diagnosis, informative concordance and misclassification matrices yielded useful insights into its role in the diagnostic process. Conclusions/Significance: The diagnostic decision support tool covered the majority of diagnoses made before or after its introduction, leading to a significant increase in the number of clinical signs recorded, suggesting this as a key beneficial consequence of its use. It may also inform approximate proportional morbidity and represent a useful epidemiological tool in poorly resourced areas

Trematode infections in cattle in Arumeru District, Tanzania are associated with irrigation

Background The relationship between the environment and infection of cattle with trematodes was studied at Arumeru District, Arusha Region, northern Tanzania. Randomly selected villages were grouped into three cattle management strata, (i) zero-grazing (ZZ) (ii) communal grazing without irrigation (ZC) and (iii) communal grazing with irrigation (ZCI). Methods Faecal samples were collected from 241 cattle, and processed using the Flukefinder® method. Snail intermediate hosts were collected with a snail scoop from the water bodies in the study villages and identified morphologically. Results The overall prevalence of F. gigantica, paramphistomes and S. bovis were 33%, 37% and 2% respectively. Prevalence for F. gigantica, paramphistomes, and S. bovis for each stratum were, zero-grazing (ZZ) (29.7%, 36.0% and 0%), communal grazing without irrigation (ZC) (6.3%, 15.0% and 3.8%) and communal grazing with irrigation (ZCI) (57.7%, 56.7% and 1.0%) respectively. The differences between strata were significant for F. gigantica (p < 0.001) and paramphistomes (p < 0.05) but not for S. bovis. Irrigation could account for the high prevalence of F. gigantica and paramphistomes in the ZCI stratum as compared to the ZZ and ZC strata. The higher prevalences of F. gigantica and paramphistomes in the ZZ stratum compared with the ZC stratum were unexpected and attributed to the practice of farmers in some ZZ stratum villages buying fodder for their cattle obtained from pastures in ZCI villages. Conclusion Trematode infections in cattle are prevalent in Arumeru District. Fasciola gigantica and paramphistomes are associated with grazing in areas with irrigation of crops. Zero-grazing of cattle does not necessarily prevent the risk of infection

Associations between trematode infections in cattle and freshwater snails in highland and lowland areas of Iringa Rural District, Tanzania

SUMMARYThe epidemiology of trematode infections in cattle was investigated within highland and lowland areas of Iringa Rural District, in southern Tanzania. Fecal samples were collected from 450 cattle in 15 villages at altitudes ranging from 696 to 1800 m above the sea level. Freshwater snails were collected from selected water bodies and screened for emergence of cercariae. The infection rates in cattle wereFasciola gigantica28·2%, paramphistomes 62·8% andSchistosoma bovis4·8%. Notably, prevalence of trematode infections in cattle was much higher in highland (altitude &gt; 1500 m) as compared with lowland (altitude &lt; 1500 m) areas and was statistically significant (P-value = 0·000) forF. giganticaand paramphistomes but not forS. bovis. The snails collected includedLymnaea natalensis, Bulinus africanus, Bulinus tropicus, Bulinus forskali, Biomphalaria pfeifferi, Melanoides tuberculataandBellamya constrictawith a greater proportion of highland (75%) than lowland (36%) water bodies harbouring snails. Altitude is a major factor shaping the epidemiology ofF. giganticaand paramphistomes infections in cattle in Iringa Rural District with greater emphasis upon control needed in highland areas.</jats:p

Herd prevalence of bovine brucellosis and analysis of risk factors in cattle in urban and peri-urban areas of the Kampala economic zone, Uganda

<p>Abstract</p> <p>Background</p> <p>Human brucellosis has been found to be prevalent in the urban areas of Kampala, the capital city of Uganda. A cross-sectional study was designed to generate precise information on the prevalence of brucellosis in cattle and risk factors for the disease in its urban and peri-urban dairy farming systems.</p> <p>Results</p> <p>The adjusted herd prevalence of brucellosis was 6.5% (11/177, 95% CI: 3.6%-10.0%) and the adjusted individual animal prevalence was 5.0% (21/423, 95% CI: 2.7% - 9.3%) based on diagnosis using commercial kits of the competitive enzyme-linked immunosorbent assay (CELISA) for <it>Brucella abortus </it>antibodies. Mean within-herd prevalence was found to be 25.9% (95% CI: 9.7% - 53.1%) and brucellosis prevalence in an infected herd ranged from 9.1% to 50%. A risk factor could not be identified at the animal level but two risk factors were identified at the herd level: large herd size and history of abortion. The mean number of milking cows in a free-grazing herd (5.0) was significantly larger than a herd with a movement restricted (1.7, p < 0.001).</p> <p>Conclusions</p> <p>Vaccination should be targeted at commercial large-scale farms with free-grazing farming to control brucellosis in cattle in and around Kampala city.</p