Effect of season on the productivity of camels (Camelus dromedarius and the prevalence of their major parasites in eastern Ethiopia

Approaches for disease prioritization and decision-making in animal health, 2000-2021: a structured scoping review

This scoping review identifies and describes the methods used to prioritize diseases for resource allocation across disease control, surveillance, and research and the methods used generally in decision-making on animal health policy. Three electronic databases (Medline/PubMed, Embase, and CAB Abstracts) were searched for articles from 2000 to 2021. Searches identified 6, 395 articles after de-duplication, with an additional 64 articles added manually. A total of 6, 460 articles were imported to online document review management software (sysrev.com) for screening. Based on inclusion and exclusion criteria, 532 articles passed the first screening, and after a second round of screening, 336 articles were recommended for full review. A total of 40 articles were removed after data extraction. Another 11 articles were added, having been obtained from cross-citations of already identified articles, providing a total of 307 articles to be considered in the scoping review. The results show that the main methods used for disease prioritization were based on economic analysis, multi-criteria evaluation, risk assessment, simple ranking, spatial risk mapping, and simulation modeling. Disease prioritization was performed to aid in decision-making related to various categories: (1) disease control, prevention, or eradication strategies, (2) general organizational strategy, (3) identification of high-risk areas or populations, (4) assessment of risk of disease introduction or occurrence, (5) disease surveillance, and (6) research priority setting. Of the articles included in data extraction, 50.5% had a national focus, 12.3% were local, 11.9% were regional, 6.5% were sub-national, and 3.9% were global. In 15.2% of the articles, the geographic focus was not specified. The scoping review revealed the lack of comprehensive, integrated, and mutually compatible approaches to disease prioritization and decision support tools for animal health. We recommend that future studies should focus on creating comprehensive and harmonized frameworks describing methods for disease prioritization and decision-making tools in animal health.

African Animal Trypanosomiasis: A Systematic Review on Prevalence, Risk Factors and Drug Resistance in Sub-Saharan Africa

African animal trypanosomiasis (AAT) a parasitic disease of livestock in sub-Saharan Africa causing tremendous loses. Sub-Saharan continental estimation of mean prevalence in both large and small domestic animals, risk factors, tsetse and non-tsetse prevalence and drug resistance is lacking. A review and meta-analysis was done to better comprehend changes in AAT prevalence and drug resistance. Publish/Perish software was used to search and extract peer-reviewed articles in Google scholar, PubMed and CrossRef. In addition, ResearchGate and African Journals Online (AJOL) were used. Screening and selection of articles from 2000-2021 was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Articles 304 were retrieved; on domestic animals 192, tsetse and non-tsetse vectors 44, risk factors 49 and trypanocidal drug resistance 30. Prevalence varied by, host animals in different countries, diagnostic methods and species of Trypanosoma. Cattle had the highest prevalence with Ethiopia and Nigeria leading, T. congolense (11.80-13.40%) and T. vivax (10.50-18.80%) being detected most. This was followed by camels and pigs. Common diagnostic method used was buffy coat microscopy. However; polymerase chain reaction (PCR), CATT and ELISA had higher detection rates. G. pallidipes caused most infections in Eastern regions while G. palpalis followed by G. mortisans in Western Africa. Eastern Africa reported more non-tsetse biting flies with Stomoxys leading. Common risk factors were, body conditions, breed type, age, sex and seasons. Ethiopia and Nigeria had the highest trypanocidal resistance 30.00-35.00% and highest AAT prevalence. Isometamidium and diminazene showed more resistance with T. congolense being most resistant species 11.00-83.00%.

Efficacy of diminazene diaceturate and isometamidium chloride hydrochloride for the treatment of Trypanosoma evansi in mice model

Diminazene diaceturate (DIM) and isometamidium chloride hydrochloride (ISMM) have been widely used for the treatment of animal trypanosomosis. We evaluated the efficacy of standard doses of DIM and ISMM followed by their double doses for the treatment of Trypanosoma evansi in experimentally infected mice. A T. evansi strain obtained from a naturally infected camel in Afar was used. 25 swiss white mice randomly divided in to five groups were inoculated with 0.2 mL of blood containing 10³ trypanosomes. At the peak of parasitemia (≈ 2 weeks post infection), groups A and B were treated with the standard dose (3.5 mg/kg body weight [BWT]) of DIM; groups C and D were treated with the standard dose (0.5 mg/kg BWT) of ISMM; and group E served as infected control. In the DIM standard dose groups, relapses and peak parasitemia were observed 20- and 25-days post treatment respectively. Similarly, relapses and peak parasitemia were observed 21- and 27-days post treatment in the ISMM standard dose groups. All mice in the control group died within two weeks post infection. Following relapses, mice were treated with the double doses of DIM (7 mg/kg BWT) or ISMM (1 mg/kg BWT). Parasitemia was not detected for 3 months following the double dose treatments. Following dexamethasone administration for 7 days, all but one mouse in the DIM group remained negative for another month. In general, although the T. evansi strain was resistant to the standard doses of DIM and ISMM their double doses completely cleared the infection.

Analysis of variation in growth and spline-based growth models for Marecha and Lassi dromedary camels

Camel is an important domestic animal that is well adapted to extremely harsh environments. Due to its multi-purpose role, the camel is gaining importance, particularly as a meat producer. Body weights at different ages and growth curves have been extensively studied in several livestock species. However, the information on the camel is very limited. We investigate patterns of variation in birth weight and weaning weight of two prominent breeds of camels in Pakistan, namely Marecha and Lassi. A further objective is not only to develop growth models which will account for systematic differences due to breed and sex but also to allow for individual variation in growth, by the application of appropriate statistical models. Birth weight, weaning, and monthly weights for a period of up to 48 months were recorded for each camel. Growth records of 137 camels consisting of 108 Marecha and 29 Lassi were obtained. Differences were detected between the two breeds, Marecha and Lassi, as well as differences between sexes, but only after 2 years of age. Beyond that, female Marecha camels had slower growth than males, whereas Lassi (mostly females) had faster growth than female Marechas. In addition, there is a sizable variation between individuals within the same breed-sex combination. The results of the present study will be of use to explore the potential of the camel as a meat producer in Pakistan.

Prevalence and distribution of Trypanosoma evansi in camels in Somaliland

The prevalence and distribution of Trypanosoma evansi (T. evansi) infection on camels in Somaliland were studied using the card agglutination test (CATT/T. evansi). A total of 2575 camels were surveyed. The overall animal-level apparent (test) prevalence in Somaliland was 26.4%. The prevalence was highest in the Sahil Region (37.3%) followed by Togdheer (28.4%), Sanaag (27.4%), and Sool (26.2%). There was a significant difference in the seroprevalence between the regions (χ² = 35.2, df = 1, P < 0.001) with the prevalence being significantly higher in Sahil than in Woqooyi Galbeed and Awdal, respectively. Camels from the eastern districts were two times more likely to be infected than camels from the western districts (P < 0.001). Herds in the coastal area were also more likely to be infected (37.0%) than herds from the inland areas (26.9%).The seroprevalence varied significantly between body condition score groups (P < 0.001) with the highest seroprevalence in camels of poor body condition (39.5%) and the lowest in camels of good body condition (18.4%) score. Animals in poor body condition were almost three times more likely to be positive than animals in good body condition (OR = 2.9; 95% CI 2.2, 3.8).

Systematic review and meta-analysis on the global distribution, host range, and prevalence of Trypanosoma evansi

BACKGROUND

Surra is an animal trypanosomosis, caused by infection with Trypanosoma evansi and leading to severe economic loss due to mortality and morbidity. Compared to tsetse-transmitted animal trypanosomoses, little attention is given to the epidemiology and control of surra. Understanding its epidemiology is a first step in local and global efforts to control the disease. We conducted a systematic review and meta-analysis of published studies on distribution, host ranges and prevalence of T. evansi infection.

METHODS

Four electronic databases were searched for publications on T. evansi that met our inclusion criteria for the systematic review. Subsets of publications were subjected to meta-analysis for the pooled prevalence of T. evansi in various hosts as determined by multiple detection methods.

RESULTS

A total of 272 references published between 1906-2017 were included. Trypanosoma evansi was reported from 48 countries; largely confined to Africa and Asia with publications on natural T. evansi infections from 77% (n = 48) of countries, contrasting with seven countries in South America, and four in Europe where T. evansi is not endemic but was imported with infected animals. Although surra is a notifiable disease, many countries do not report surra cases to OIE. Trypanosoma evansi was mainly reported from dromedary camels in Africa and the Middle East, water buffaloes, cattle, dogs and horses in East and Southeast Asia. In South America, the acute form of the disease was reported in horses and dogs. Surra was also reported in a wide range of wild animals. Some rare human cases occurred in India and Vietnam. Meta-analysis on a subset of 165 publications indicated pooled prevalence of T. evansi in domestic animals ranging from 14-31%, 6-28% and 2-9% using respectively antibody detection, molecular and parasitological tests, with camels as the most affected, followed by buffalo and cattle.

CONCLUSIONS

This study illustrates that T. evansi affects a wide range of domestic and wild animals in Africa, Asia and South America with highest prevalence observed in dromedary camels. For successful control of T. evansi, both locally and globally, the role of wild animals in the epidemiology of surra needs further investigation.

Estimating the economic impact of Trypanosoma evansi infection on production of camel herds in Somaliland

The traditional livestock sector in Somalia is based on nomadic pastoralism where sheep, goats and camels are herded in large numbers. Data from 1609 females (27 % lactating) and 550 males (26 % exported) belonging to 40 pastoralists were analysed in this study. The expected amount of revenue the herders could lose per year in the studied area was estimated at US$404,630 being made up of US$314,630 from decreased milk yield and US$90,000 from reduced market value of exported animals. However, all the camels in Somaliland are at risk of acquiring surra infection, and therefore extrapolating the current findings to the total population could potentially lose US$223,164,000. This highlights the loss in the magnitude of US$164,253,600 from decreased milk yield and US$58,910,400 from body condition loss. Overall, the benefit in controlling Trypanosoma evansi infection in the study area was US$398,880 (n = 2159). On average, US$720 was saved per head per year from improved milk production in treated animals and US$615 from the increased value of exported camels. It is concluded that all three-treatment options evaluated were economically beneficial strategies; however, the biannual treatment of seropositive camels in the herds was the best financial option.

Milk production and feeding behavior in the camel (Camelus dromedarius) during 4 watering regimens

Camels survive and produce milk during recurrent prolonged hot and dry periods. The objective was to evaluate how different watering intervals affected milk production and feeding. Eight lactating camels (Camelus dromedarius) were recruited and subjected to 4 watering regimens in a Latin square design experiment performed at Haramaya University in Ethiopia. Each regimen lasted 16 d with 5 d of daily watering between periods: water was offered at 1,315 h once daily (W1); on d 4, 8, 12, and 16 (W4); on d 8 and 16 (W8); and on d 16 (W16). One camel became sick in the second period and its results were excluded. Camels were kept in a pen with minimal shade and a noon temperature of 30.9±0.1°C. They had free access to hay and were offered 2 kg of concentrates 3 times daily. At noon on d 1, 4, 8, 12, and 16, a blood sample was taken from the jugular vein before watering. All calves were kept together in a separate pen. Morning and afternoon calves stimulated milk let-down before the camels were hand-milked, after which the calves suckled, emptying the udder. Camels maintained the milk volume during water deprivation for about 1 wk, but they produced less milk during the second week during W16. Morning milk osmolality increased from 315±3 on d 1 to 333±3 mosm/kg on d 4 during W4 and from 321±3 on d 1 to 342±3 mosm/kg on d 8 during W8. After watering at 1315 h, milk osmolality decreased to 316±3 and 323±3 mosm/kg, respectively, the same afternoon and then increased during recurrent water deprivation to 338±3 (W4) and 347±3 mosm/kg (W8) on d 16, respectively. During W16, osmolality increased from 318±3 to 336±3 mosm/kg during the first 4 d of water deprivation, but during the remaining 12 d the further rise in osmolality was not higher compared with that on d 4. The change in milk osmolality was linearly correlated to plasma osmolality (r=0.8), but milk lactose content did not increase. Contrary to widespread belief, camels did not dilute their milk when dehydrated. Instead milk osmolality increased in parallel to blood osmolality. This study provides further support to earlier observations on camels' adaptation to their environment.