Field validation of clinical and laboratory diagnosis of wildebeest associated malignant catarrhal fever in cattle

Explanatory models and animal health-seeking behavior for East Coast fever in rural Kenya: an ethnographic study

Introduction

Explanatory models of disease focus on individuals' and groups' understandings of diseases, revealing a disconnect between livestock keepers and animal health providers. Animal health providers rely on models grounded in their veterinary training and experience. At the same time, livestock keepers may construct models based on traditional knowledge and their lived experience with East Coast fever in their cattle herds. To better understand East Coast fever and develop more efficient management strategies, this ethnographic study used the explanatory models' framework to provide a structured way for comprehending and contrasting different beliefs and understandings of East Coast fever as perceived by the livestock keepers across the different livestock production systems.

Method

Multiple data collection methods were employed, including unstructured observations, 30 in-depth interviews (IDIs), 18 focus group discussions (FGDs), and 25 key informant interviews (KIIs).

Results

Adult cattle, calves and sheep were perceived as susceptible to East Coast fever. However, there were varying perceptions of livestock susceptible to East Coast fever in the different livestock production systems. East Coast fever was attributed to multiple factors, including ticks, tsetse flies, mosquitos, birds, stagnant, dirty, or contaminated water, and livestock-wildlife interactions. However, some aspects were specific to the production system. Livestock keepers classified diseases based on observable signs, grouping diseases with similar signs under the same classification. Moreover, livestock keepers described different forms of East Coast fever ranging from treatable to fatal, which could be distinguished by the signs they presented. Self-treatment with drugs from the local agro-vet shops was the initial course of action during suspected cases of East Coast fever. Animal health practitioners were the last resort if self-treatment did not produce the desired outcome. Livestock keepers perceived avoidance of stagnant or contaminated water, tick control, and fencing as effective control measures for East Coast fever in their livestock herd. Very few livestock keepers were aware of an East Coast fever vaccine.

Discussion

Mechanistic explanations hold little significance in controlling East Coast fever. Instead, understanding and addressing livestock keepers' beliefs regarding ECF is crucial for promoting behaviors that support interventions across different livestock production systems.

Molecular Tools to Identify and Characterize Malignant Catarrhal Fever Viruses (MCFV) of Ruminants and Captive Artiodactyla

The family Herpesviridae includes viruses identified in mammals, birds and reptiles. All herpesviruses share a similar structure, consisting of a large linear double-stranded DNA genome surrounded by a proteic icosahedral capsid further contained within a lipidic bilayer envelope. The continuous rise of genetic variability and the evolutionary selective pressure underlie the appearance and consolidation of novel viral strains. This applies also to several gamma(γ)-herpesviruses, whose role as primary pathogen has been often neglected and, among these to newly emerged viruses or virus variants responsible for the development of Malignant Catarrhal Fever (MCF) or MCF-like disease. The identification of γ-herpesviruses adapted to new zoological hosts requires specific molecular tools for detection and characterization. These viruses can cause MCF in livestock and wild animals, a disease generally sporadic but with serious welfare implications and which, in many cases, leads to death within a few days from the appearance of the clinical signs. In the absence of a vaccine, the first step to improve disease control is based on the improvement of molecular tools to identify and characterize these viruses, their phylogenetic relationships and evolutionary interaction with the host species. A Panherpes PCR-specific test, based on the conserved DNA polymerase gene, employing consensus/degenerate and deoxyinosine-substituted primers followed by sequencing, is still the preferred diagnostic test to confirm and characterize herpesviral infections. The drawback of this test is the amplification of a relatively short sequence, which makes phylogenetic analysis less stringent. Based on these diagnostic requirements, and with a specific focus on γ-herpesviruses, the present review aims to critically analyze the currently available methods to identify and characterize novel MCFV strains, to highlight advantages and drawbacks and to identify the gaps to be filled in order to address research priorities. Possible approaches for improving or further developing these molecular tools are also suggested.

Development of a recombinant ELISA for ovine herpesvirus 2, suitable for use in sheep

The minor capsid protein of ovine herpesvirus 2, identified as a potential antigen for serological testing, was over-expressed and purified to allow its assessment in ELISA. The corresponding gene sequence (OvHV-2 orf65, Ov65) was modified to incorporate epitope tags and internal restriction enzyme sites in an E. coli codon-optimised version of the gene. This codon-optimised gene was then subject to internal deletions to identify regions of the protein that could be removed while maintaining protein solubility and antigenicity. It was found that a derivative with deletion of the conserved 5'-end of the gene (Ov65delB) expressed a polypeptide that was soluble when over-expressed in bacteria and was detected by OvHV-2 specific sera. Proteomic analysis of the affinity purified Ov65delB showed that it contained multiple predicted Ov65 tryptic peptides but also showed contamination by co-purifying E. coli proteins. An indirect ELISA, based on this affinity-purified OV65delB, was optimised for use with sheep and cattle samples and cut-off values were established based on known negative serum samples. Analysis of groups of samples that were either presumed infected (UK sheep) or tested OvHV-2 positive or negative by PCR (cattle MCF diagnostic samples) showed that the assay had 95 % sensitivity and 96 % specificity for sheep serum; and 80 % sensitivity and 95 % specificity for cattle serum. The lower sensitivity with cattle samples appeared to be due to a lack of serological response in some MCF-affected cattle. This recombinant antigen therefore shows promise as the basis of an inexpensive, simple and reliable test that can be used to detect OvHV-2-specific antibody responses in both MCF-affected animals and in OvHV-2 reservoir hosts.

Prioritizing smallholder animal health needs in East Africa, West Africa, and South Asia using three approaches: Literature review, expert workshops, and practitioner surveys

Managing the health needs of livestock contributes to reducing poverty and improving the livelihoods of smallholder and pastoralist livestock keepers globally. Animal health practitioners, producers, policymakers, and researchers all must prioritize how to mobilize limited resources. This study employed three approaches to prioritize animal health needs in East and West Africa and South Asia to identify diseases and syndromes that impact livestock keepers. The approaches were a) systematic literature review, b) a series of expert workshops, and c) a practitioner survey of veterinarians and para-veterinary professionals. The top constraints that emerged from all three approaches include endo/ ectoparasites, foot and mouth disease, brucellosis, peste des petits ruminants, Newcastle disease, and avian influenza. Expert workshops additionally identified contagious caprine pleuropneumonia, contagious bovine pleuropneumonia, mastitis, and reproductive disorders as constraints not emphasized in the literature review. Practitioner survey results additionally identified nutrition as a constraint for smallholder dairy and pastoralist small ruminant production. Experts attending the workshops agreed most constraints can be managed using existing veterinary technologies and best husbandry practices, which supports a shift away from focusing on individual diseases and new technologies towards addressing systemic challenges that limit access to veterinary services and inputs. Few research studies focused on incidence/ prevalence of disease and impact, suggesting better incorporation of socio-economic impact measures in future research would better represent the interests of livestock keepers.

A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle

Wildebeest-associated malignant catarrhal fever (WA-MCF), a fatal disease of cattle caused by alcelaphine herpesvirus 1 (AlHV-1), is one of the most important seasonal diseases of cattle in wildebeest endemic areas, with annual incidence reaching 10%. Here we report efficacy of over 80% for a vaccine based on the attenuated AlHV-1 C500 strain, in preventing fatal WA-MCF in cattle exposed to natural wildebeest challenge. The study was conducted at Kapiti Plains Ranch Ltd, south-east of Nairobi, Kenya. In 2016, 146 cattle were selected for a randomised placebo-controlled trial. Cattle were stratified according to breed and age and randomly assigned to groups given vaccine or culture medium mixed with Emulsigen®. Cattle received prime and boost inoculations one month apart and few adverse reactions (n = 4) were observed. Indirect ELISA demonstrated that all cattle in the vaccine group developed a serological response to AlHV-1. The study herd was grazed with wildebeest from one month after booster vaccination. Three cattle, two that received vaccine and one control, succumbed to conditions unrelated to WA-MCF before the study ended. Twenty-five cattle succumbed to WA-MCF; four of the remaining 71 cattle in the vaccine group (5.6%) and 21 of the remaining 72 control cattle (29.2%; χ² = 13.6, df = 1, p < 0.001). All of the WA-MCF affected cattle were confirmed by PCR to be infected with AlHV-1 and in 23 cases exhibited histopathology typical of WA-MCF. Vaccine efficacy was determined to be 80.6% (95% CI 46.5-93.0%). Hence, the AlHV-1 C500 vaccine is a safe and potentially effective novel method for controlling WA-MCF in cattle. The implementation of this vaccine may have significant impacts on marginalised cattle keeping communities.