Rift Valley Fever Outbreak in Livestock, Mozambique, 2014.

In early 2014, abortions and death of ruminants were reported on farms in Maputo and Gaza Provinces, Mozambique. Serologic analysis and quantitative and conventional reverse transcription PCR confirmed the presence of Rift Valley fever virus. The viruses belonged to lineage C, which is prevalent among Rift Valley fever viruses in southern Africa.

Variation and covariation in strongyle infection in East African shorthorn zebu calves.

Parasite burden varies widely between individuals within a population, and can covary with multiple aspects of individual phenotype. Here we investigate the sources of variation in faecal strongyle eggs counts, and its association with body weight and a suite of haematological measures, in a cohort of indigenous zebu calves in Western Kenya, using relatedness matrices reconstructed from single nucleotide polymorphism (SNP) genotypes. Strongyle egg count was heritable (h(2) = 23.9%, s.e. = 11.8%) and we also found heritability of white blood cell counts (WBC) (h(2) = 27.6%, s.e. = 10.6%). All the traits investigated showed negative phenotypic covariances with strongyle egg count throughout the first year: high worm counts were associated with low values of WBC, red blood cell count, total serum protein and absolute eosinophil count. Furthermore, calf body weight at 1 week old was a significant predictor of strongyle EPG at 16-51 weeks, with smaller calves having a higher strongyle egg count later in life. Our results indicate a genetic basis to strongyle EPG in this population, and also reveal consistently strong negative associations between strongyle infection and other important aspects of the multivariate phenotype.

A longitudinal assessment of the serological response to Theileria parva and other tick-borne parasites from birth to one year in a cohort of indigenous calves in western Kenya.

Tick-borne diseases are a major impediment to improved productivity of livestock in sub-Saharan Africa. Improved control of these diseases would be assisted by detailed epidemiological data. Here we used longitudinal, serological data to determine the patterns of exposure to Theileria parva, Theileria mutans, Babesia bigemina and Anaplasma marginale from 548 indigenous calves in western Kenya. The percentage of calves seropositive for the first three parasites declined from initial high levels due to maternal antibody until week 16, after which the percentage increased until the end of the study. In contrast, the percentage of calves seropositive for T. mutans increased from week 6 and reached a maximal level at week 16. Overall 423 (77%) calves seroconverted to T. parva, 451 (82%) to T. mutans, 195 (36%) to B. bigemina and 275 (50%) to A. marginale. Theileria parva antibody levels were sustained following infection, in contrast to those of the other three haemoparasites. Three times as many calves seroconverted to T. mutans before seroconverting to T. parva. No T. parva antibody response was detected in 25 calves that died of T. parva infection, suggesting that most deaths due to T. parva are the result of acute disease from primary exposure.

Evidence of lumpy skin disease virus over-wintering by transstadial persistence in Amblyomma hebraeum and transovarial persistence in Rhipicephalus decoloratus ticks.

Lumpy skin disease is a debilitating cattle disease caused by the lumpy skin disease virus (LSDV), belonging to the genus Capripoxvirus. Epidemics of the disease usually occur in summer, when insect activity is high. Limited information is available on how LSDV persists during inter-epidemic periods. Transmission of LSDV by mosquitoes such as Aedes aegypti has been shown to be mechanical, there is no carrier state in cattle and the role of wildlife in the epidemiology of the disease seems to be of minor importance. Recent studies in ticks have shown transstadial persistence of LSDV in Rhipicephalus appendiculatus and Amblyomma hebraeum as well as transovarial persistence of the virus in Rhipicephalus decoloratus, R. appendiculatus and A. hebraeum. The over-wintering of ticks off the host as part of their life cycles is well known: A. hebraeum and R. appendiculatus over-winter, for example, on the ground as engorged nymphs/unfed (emergent) adults while R. decoloratus over-winters on the ground as engorged females. In this study, transstadial and transovarial persistence of LSDV from experimentally infected A. hebraeum nymphs and R. decoloratus females after exposure to cold temperatures of 5 °C at night and 20 °C during the day for 2 months was reported. This observation suggests possible over-wintering of the virus in these tick species.

Mechanical transmission of lumpy skin disease virus by Rhipicephalus appendiculatus male ticks.

Lumpy skin disease (LSD) is an economically important, acute or sub-acute, viral disease of cattle that occurs across Africa and in the Middle East. The aim of this study was to investigate if lumpy skin disease virus (LSDV) can be transmitted mechanically by African brown ear ticks (Rhipicephalus appendiculatus Neum.). Laboratory-bred R. appendiculatus males were fed on experimentally infected viraemic 'donor' cattle. Partially fed male ticks were then transferred to feed on an uninfected 'recipient' cow. The recipient animal became viraemic, showed mild clinical signs of LSD and seroconverted. Additionally, R. appendiculatus males were found to transmit LSDV through feeding on skin lacking visible lesions, demonstrating that viraemic animals without lesions at the feeding site of ticks may be a source of infection. This is the first time that transmission of poxviruses by a tick species has been demonstrated and the importance of this mode of transmission in the spread of LSDV in endemic settings is discussed.

Parasite co-infections show synergistic and antagonistic interactions on growth performance of East African zebu cattle under one year.

The co-occurrence of different pathogen species and their simultaneous infection of hosts are common, and may affect host health outcomes. Co-infecting pathogens may interact synergistically (harming the host more) or antagonistically (harming the host less) compared with single infections. Here we have tested associations of infections and their co-infections with variation in growth rate using a subset of 455 animals of the Infectious Diseases of East Africa Livestock (IDEAL) cohort study surviving to one year. Data on live body weight, infections with helminth parasites and haemoparasites were collected every 5 weeks during the first year of life. Growth of zebu cattle during the first year of life was best described by a linear growth function. A large variation in daily weight gain with a range of 0·03-0·34 kg, and a mean of 0·135 kg (0·124, 0·146; 95% CI) was observed. After controlling for other significant covariates in mixed effects statistical models, the results revealed synergistic interactions (lower growth rates) with Theileria parva and Anaplasma marginale co-infections, and antagonistic interactions (relatively higher growth rates) with T. parva and Theileria mutans co-infections, compared with infections with T. parva only. Additionally, helminth infections can have a strong negative effect on the growth rates but this is burden-dependent, accounting for up to 30% decrease in growth rate in heavily infected animals. These findings present evidence of pathogen-pathogen interactions affecting host growth, and we discuss possible mechanisms that may explain observed directions of interactions as well as possible modifications to disease control strategies when co-infections are present.

Mortality in East African shorthorn zebu cattle under one year: predictors of infectious-disease mortality.

BACKGROUND: Infectious livestock diseases remain a major threat to attaining food security and are a source of economic and livelihood losses for people dependent on livestock for their livelihood. Knowledge of the vital infectious diseases that account for the majority of deaths is crucial in determining disease control strategies and in the allocation of limited funds available for disease control. Here we have estimated the mortality rates in zebu cattle raised in a smallholder mixed farming system during their first year of life, identified the periods of increased risk of death and the risk factors for calf mortality, and through analysis of post-mortem data, determined the aetiologies of calf mortality in this population. A longitudinal cohort study of 548 zebu cattle was conducted between 2007 and 2010. Each calf was followed during its first year of life or until lost from the study. Calves were randomly selected from 20 sub-locations and recruited within a week of birth from different farms over a 45 km radius area centered on Busia in the Western part of Kenya. The data comprised of 481.1 calf years of observation. Clinical examinations, sample collection and analysis were carried out at 5 week intervals, from birth until one year old. Cox proportional hazard models with frailty terms were used for the statistical analysis of risk factors. A standardized post-mortem examination was conducted on all animals that died during the study and appropriate samples collected. RESULTS: The all-cause mortality rate was estimated at 16.1 (13.0-19.2; 95% CI) per 100 calf years at risk. The Cox models identified high infection intensity with Theileria spp., the most lethal of which causes East Coast Fever disease, infection with Trypanosome spp., and helminth infections as measured by Strongyle spp. eggs per gram of faeces as the three important infections statistically associated with infectious disease mortality in these calves. Analysis of post-mortem data identified East Coast Fever as the main cause of death accounting for 40% of all deaths, haemonchosis 12% and heartwater disease 7%. CONCLUSION: The findings demonstrate the impact of endemic parasitic diseases in indigenous animals expected to be well adapted against disease pressures. Additionally, agreement between results of Cox models using data from simple diagnostic procedures and results from post-mortem analysis underline the potential use such diagnostic data to reduce calf mortality. The control strategies for the identified infectious diseases have been discussed.

Design and descriptive epidemiology of the Infectious Diseases of East African Livestock (IDEAL) project, a longitudinal calf cohort study in western Kenya.

BACKGROUND: There is a widely recognised lack of baseline epidemiological data on the dynamics and impacts of infectious cattle diseases in east Africa. The Infectious Diseases of East African Livestock (IDEAL) project is an epidemiological study of cattle health in western Kenya with the aim of providing baseline epidemiological data, investigating the impact of different infections on key responses such as growth, mortality and morbidity, the additive and/or multiplicative effects of co-infections, and the influence of management and genetic factors.A longitudinal cohort study of newborn calves was conducted in western Kenya between 2007-2009. Calves were randomly selected from all those reported in a 2 stage clustered sampling strategy. Calves were recruited between 3 and 7 days old. A team of veterinarians and animal health assistants carried out 5-weekly, clinical and postmortem visits. Blood and tissue samples were collected in association with all visits and screened using a range of laboratory based diagnostic methods for over 100 different pathogens or infectious exposures. RESULTS: The study followed the 548 calves over the first 51 weeks of life or until death and when they were reported clinically ill. The cohort experienced a high all cause mortality rate of 16% with at least 13% of these due to infectious diseases. Only 307 (6%) of routine visits were classified as clinical episodes, with a further 216 reported by farmers. 54% of calves reached one year without a reported clinical episode. Mortality was mainly to east coast fever, haemonchosis, and heartwater. Over 50 pathogens were detected in this population with exposure to a further 6 viruses and bacteria. CONCLUSION: The IDEAL study has demonstrated that it is possible to mount population based longitudinal animal studies. The results quantify for the first time in an animal population the high diversity of pathogens a population may have to deal with and the levels of co-infections with key pathogens such as Theileria parva. This study highlights the need to develop new systems based approaches to study pathogens in their natural settings to understand the impacts of co-infections on clinical outcomes and to develop new evidence based interventions that are relevant.

Detection of lumpy skin disease virus in saliva of ticks fed on lumpy skin disease virus-infected cattle.

Lumpy skin disease is an economically important disease of cattle that is caused by the lumpy skin disease virus (LSDV), which belongs to the genus Capripoxvirus. It is endemic in Africa and outbreaks have also been reported in the Middle-East. Transmission has mostly been associated with blood-feeding insects but recently, the authors have demonstrated mechanical transmission by Rhipicephalus appendiculatus as well as mechanical/intrastadial and transstadial transmission by Amblyomma hebraeum. Saliva is the medium of transmission of pathogens transmitted by biting arthropods and, simultaneously, it potentiates infection in the vertebrate host. This study aimed to detect LSDV in saliva of A. hebraeum and R. appendiculatus adult ticks fed, as nymphs or as adults, on LSDV-infected animals, thereby also demonstrating transstadial or mechanical/intrastadial passage of the virus in these ticks. Saliva samples were tested for LSDV by real-time PCR and virus isolation. Supernatants obtained from virus isolation were further tested by real-time PCR to confirm that the cytopathic effects observed were due to LSDV. Lumpy skin disease virus was detected, for the first time, in saliva samples of both A. hebraeum and R. appendiculatus ticks. At the same time, mechanical/intrastadial and transstadial passage of the virus was demonstrated and confirmed in R. appendiculatus and A. hebraeum.

Reflections on IDEAL: What we have learnt from a unique calf cohort study.

The year 2020 marks a decade since the final visit was made in the 'Infectious Diseases of East African Livestock' (IDEAL) project. However, data generation from samples obtained during this ambitious longitudinal study still continues. As the project launches its extensive open-access database and biobank to the scientific community, we reflect on the challenges overcome, the knowledge gained, and the advantages of such a project. We discuss the legacy of the IDEAL project and how it continues to generate evidence since being adopted by the Centre for Tropical Livestock Genetics and Health (CTLGH). We also examine the impact of the IDEAL project, from the authors perspective, for each of the stakeholders (the animal, the farmer, the consumer, the policy maker, the funding body, and the researcher and their institution) involved in the project and provide recommendations for future researchers who are interested in running longitudinal field studies.

Integrating global animal health, public health and tropical animal health issues into the veterinary curriculum: a South African/African perspective.

The globalisation of trade and food, the increased volume and speed of international travel, climate change, and the related escalation of emerging and re-emerging infectious diseases mean that countries are now more interconnected and interdependent than ever before. Africa is beleaguered by a range of endemic infectious and parasitic tropical diseases which, due to its diverse wildlife populations and indigenous livestock, can serve as a reservoir of high-impact or transboundary diseases and play a role in the emergence of disease, particularly at the wildlife, domestic animal and human interfaces. It is therefore essential to integrate animal and public health issues into the veterinary curriculum. Veterinary training in most parts of sub-Saharan Africa has focused on producing veterinarians to serve the livestock sector although socio-economic changes and privatisation of Veterinary Services have caused curriculum adjustments, as have globalisation and the increased risk of the spread of transboundary diseases. In South Africa, undergraduate veterinary training is more clinically oriented than in other regions. Animal and public health issues are covered in the curriculum, although their global relevance is not emphasised. The authors describe the undergraduate veterinary curriculum and summarise post-graduate programmes in South Africa. They also discuss a more comprehensive core-elective approach to the current curriculum and the need to adapt to new challenges facing the profession. Finally, they examine the potential use of innovative technology in undergraduate and post-graduate training and professional development, the importance of regional and international collaboration and the accreditation and recognition of veterinary training.

Climate change and animal health in Africa.

Climate change is expected to have direct and indirect impacts on African livestock. Direct impacts include increased ambient temperature, floods and droughts. Indirect impacts are the result of reduced availability of water and forage and changes in the environment that promote the spread of contagious diseases through increased contact between animals, or increased survival or availability of the agent or its intermediate host. The distribution and prevalence of vector-borne diseases may be the most significant effect of climate change. The potential vulnerability of the livestock industry will depend on its ability to adapt to such changes. Enhancing this adaptive capacity presents a practical way of coping with climate change. Adaptive capacity could be increased by enabling the African livestock owner to cope better with animal health problems through appropriate policy measures and institutional support. Developing an effective and sustainable animal health service, associated surveillance and emergency preparedness systems and sustainable disease control and prevention programmes is perhaps the most important strategy for dealing with climate change in many African countries.

Cloning and expression of Rift Valley fever virus nucleocapsid (N) protein and evaluation of a N-protein based indirect ELISA for the detection of specific IgG and IgM antibodies in domestic ruminants.

Serodiagnosis of Rift Valley fever (RVF) currently relies on the use of live or inactivated whole virus as antigens. The recombinant nucleocapsid (N) protein of RVF virus was tested for diagnostic applicability in an indirect enzyme-linked immunosorbent assay (I-ELISA), using sera from experimentally infected sheep (n=128), vaccinated sheep (n=240), and field-collected sera from sheep (n=251), goats (n=362) and cattle (n=100). The N-protein based I-ELISA performed at least as good as VN and HI tests. In goat the diagnostic sensitivity (D-Sn) and specificity (D-Sp) of the I-ELISA was 100% when using the anti-species IgG conjugate. Using protein G as a detection system, the D-Sn and D-Sp in goats were 99.4% and 99.5%, in sheep field sera both 100%, in cattle 100% and 98.3%, respectively. The I-ELISA based on recombinant N-protein has the potential to complement the traditional assays for serodiagnosis of RVF. Advantages of the N-protein are its safety, stability and cost-effectiveness in use and production.

Seroprevalence of respiratory viral pathogens of indigenous calves in Western Kenya.

Most studies of infectious diseases in East African cattle have concentrated on gastro-intestinal parasites and vector-borne diseases. As a result, relatively little is known about viral diseases, except for those that are clinically symptomatic or which affect international trade such as foot and mouth disease, bluetongue and epizootic haemorrhagic disease. Here, we investigate the seroprevalence, distribution and relationship between the viruses involved in respiratory disease, infectious bovine rhinotracheitis virus (IBR), bovine parainfluenza virus Type 3 (PIV3) and bovine viral diarrhoea virus (BVDV) in East African Shorthorn Zebu calves. These viruses contribute to the bovine respiratory disease complex (BRD) which is responsible for major economic losses in cattle from intensive farming systems as a result of pneumonia. We found that calves experience similar risks of infection for IBR, PIV3, and BVDV with a seroprevalence of 20.9%, 20.1% and 19.8% respectively. We confirm that positive associations exist between IBR, PIV3 and BVDV; being seropositive for any one of these three viruses means that an individual is more likely to be seropositive for the other two viruses than expected by chance.

The detection of lumpy skin disease virus in samples of experimentally infected cattle using different diagnostic techniques.

Lumpy skin disease (LSD) is a disease of cattle, primarily in Africa and Madagascar and rarely in the Middle East. It is caused by a capripoxvirus that belongs to the family Poxviridae. The disease is of economic importance in endemic areas. Effective control of LSD requires accurate and rapid laboratory techniques to confirm a tentative clinical diagnosis. Comparative studies on different diagnostic tests used at different stages of the disease have not been done. The aim of this study was to compare several of these tests. Six seronegative bulls, between 11 and 20 months of age, were infected intravenously and kept in an insect-free facility. The course of the infection was monitored. During a 3-month period blood samples and skin biopsies were collected for virus isolation and polymerase chain reaction (PCR). Skin biopsies were also examined using transmission electron microscopy (TEM). The incubation period in infected animals varied from 4-5 days. The length of the viraemic period did not correlate with the severity of clinical disease. Viraemia was detected from 1-12 days using virus isolation and from 4-11 days using the PCR, which is longer than has previously been reported. Virus was isolated from skin biopsies until Day 39 post infection (p.i.) and PCR could demonstrate viral DNA until Day 92 p.i. Transmission electron microscopy of negatively stained skin biopsies detected LSD virus only in one of the four bulls that developed skin lesions until Day 33 p.i. The PCR was a fast and sensitive method to demonstrate viral DNA in blood and skin samples. It could detect viral nucleic acid in skin lesions 53 days longer than virus isolation. Virus isolation from blood and skin samples was sensitive and reliable, but as a single test it may be too time-consuming to use although this depends on how rapidly the diagnosis must be confirmed. In conclusion, this study showed the PCR to be superior in detecting LSD virus from blood and skin samples. However, virus isolation is still required when the infectivity of the LSD virus is to be determined.

Lumpy skin disease: attempted propagation in tick cell lines and presence of viral DNA in field ticks collected from naturally-infected cattle.

Lumpy skin disease (LSD) is of substantial economic importance for the cattle industry in Africa and the Near and Middle East. Several insect species are thought to transmit the disease mechanically. Recent transmission studies have demonstrated the first evidence for a role of hard (ixodid) ticks as vectors of lumpy skin disease virus (LSDV). The aim of this study was to attempt in vitro growth of the virus in Rhipicephalus spp. tick cell lines and investigate in vivo the presence of the virus in ticks collected from cattle during LSD outbreaks in Egypt and South Africa. No evidence was obtained for replication of LSDV in tick cell lines although the virus was remarkably stable, remaining viable for 35 days at 28°C in tick cell cultures, in growth medium used for tick cells and in phosphate buffered saline. Viral DNA was detected in two-thirds of the 56 field ticks, making this the first report of the presence of potentially virulent LSDV in ticks collected from naturally infected animals.

Evidence of transstadial and mechanical transmission of lumpy skin disease virus by Amblyomma hebraeum ticks.

Lumpy skin disease (LSD) is an economically important disease caused by LSD virus (LSDV), a Capripoxvirus, characterized by fever and circumscribed skin lesions. It is suspected to be transmitted mechanically by biting flies. To assess the vector potential of Amblyomma hebraeum in transmission of LSDV, mechanical/intrastadial and transstadial modes of transmission of the virus by this tick species were investigated. Two cattle were artificially infected as sources (donors) of infection to ticks. Ticks were infected as either nymphs or adults. Male A. hebraeum ticks were partially fed on donor animals and transferred to recipient animals to test for mechanical/intrastadial transmission. Nymphal A. hebraeum were fed to repletion on donor animals. The emergent adult ticks were placed on recipient animals to test for transstadial transmission of the virus. Successful transmission of LSDV infection was determined in recipient animals by monitoring development of clinical signs, testing of blood for the presence of LSDV by real-time PCR, virus isolation and the serum neutralization test. This report provides further evidence of mechanical/intrastadial and, for the first time, transstadial transmission of LSDV by A. hebraeum. These findings implicate A. hebraeum as a possible maintenance host in the epidemiology of the disease.

The pathology of Rift Valley fever. I. Lesions occurring in natural cases in new-born lambs.

A widespread epizootic of Rift Valley fever occurred in the Republic of South Africa and South West Africa during 1974--75. This is a report on the gross pathology of 34 new-born lambs and the histopathology of 93 new-born lambs that died during this outbreak. The liver was affected in every case and showed the most pronounced lesions. The organ was grossly enlarged in most cases, with scattered greyish-white necrotic foci 1--2 mm in diameter and haemorrhages of varying size throughout. Haemorrhages were also frequently seen in the mucosa of the abomasum. The massive diffuse necrosis of hepatocytes (pannecrosis) associated with well-demarcated foci of primary coagulative necrosis, present in 100% of the cases examined, was characteristic of the histopathology of the new-born lamb. Bile thrombi were noticed in the livers of 31% of the lambs and intranuclear inclusions in 49% of the cases. The diagnostic significance of the microscopic liver lesions is discussed. Focal necrosis and haemorrhages were frequently seen in the adrenal cortex while generalized destruction of lymphocytes in the lymph nodes and spleen occurred in many of the animals. In addition, the following hitherto undescribed or previously not well-documented lesions are recorded: (i) mineralization of single or groups of necrotic hepatocytes in 62% of the livers: (ii) pyknosis and karyorrhexis of the cellular elements in the glomeruli and a hyalinized appearance of many of these affected glomeruli; and (iii) necrosis of the tips of the villi in the small intestine in some of the animals.

The pathology of Rift Valley fever. II. Lesions occurring in field cases in adult cattle, calves and aborted foetuses.

Since the original description of Rift Valley fever in sheep, cattle and man in the Rift Valley in Kenya in 1931, very little has been published on the disease in cattle. This report deals with the macroscopic and microscopic pathology of field cases of Rift Valley fever in 22 adult cattle, 8 calves and 8 aborted foetuses. The microscopic liver lesions in 13 adult cattle were characterized by marked centri- and midzonal eosinophilic necrosis, involving almost 2/3 of the lobules, and accompanied by sparsely distributed primary foci of necrosis. In 3 animals, however, the hepatic lesions were more focal in nature, while a massive hepatic necrosis was evident in 6 others. In calves, the lesions in the liver ranged from cases showing numerous haphazardly scattered primary foci of necrosis to cases where the latter were accompanied by eosinophilic necrosis of the remaining hepatocytes in the lobules. Vascular lesions, thrombosis and sinusoidal fibrin deposits were sometimes seen in the livers of both calves and adult cattle. Although the aborted foetuses were in a fairly advanced state of autolysis, it was still possible to make a diagnosis of Rift Valley fever from the characteristic lesions which were similar to those reported for new-born lambs. Other noteworthy lesions in adult cattle and calves included pyknosis and karyorrhexis of lymphocytes in the spleen and lymph nodes, widespread serosal and visceral haemorrhages which were sometimes accompanied by copious free blood in the gastrointestinal tract, and a nephrosis.

Photosensitivity in South Africa. IV. Pathological changes in the liver in ovine photosensitivity caused by the plant Asaemia axillaris (Thunb.) Harv. Ex Jackson.

Hepatic lesions in 4 field cases of ovine hepatogenous photosensitization caused by the plant, Asaemia axillaris (Thunb.) Harv. Ex Jackson, are described. The liver was usually swollen, friable and yellowish-brown, with distinct lobulation. Microscopically, the lesions ranged from peripheral coagulative necrosis in 1 animal to others with scattered single cell or small foci of necrosis as well as hepatocellular degeneration and unrest, ductular proliferation, portal fibroplasia and cholestasis. The liver lesions are compared with those of previously reported experimental cases of A. axillaris poisoning in sheep. The significance of zonal necrosis and factors that may have a bearing on their production in different hepatotoxic plant poisoning in sheep and cattle in South Africa are discussed.