Hetron Mweemba Munang'andu

Stress-induced reversion to virulence of infectious pancreatic necrosis virus in naïve fry of Atlantic salmon (Salmo salar L.).

We have studied stress-induced reversion to virulence of infectious pancreatic necrosis virus (IPNV) in persistently infected Atlantic salmon (Salmo salar L.) fry. Naïve fry were persistently infected with a virulent strain (T217A221 of major structural virus protein 2, VP2) or a low virulent (T217T221) variant of IPNV. The fry were infected prior to immunocompetence as documented by lack of recombination activating gene-1, T-cell receptor and B-cell receptor mRNA expression at time of challenge. The fish were followed over 6 months and monitored monthly for presence of virus and viral genome mutations. No mutation was identified in the TA or TT group over the 6 months period post infection. Six months post infection TA and TT infected groups were subject to daily stress for 7 days and then sampled weekly for an additional period of 28 days post stress. Stress-responses were documented by down-regulation of mRNA expression of IFN-α1 and concomitant increase of replication levels of T217T221 infected fish at day 1 post stress. By 28 days post stress a T221A reversion was found in 3 of 6 fish in the T217T221 infected group. Sequencing of reverted isolates showed single nucleotide peaks on chromatograms for residue 221 for all three isolates and no mix of TA and TT strains. Replication fitness of reverted (TA) and non-reverted (TT) variants was studied in vitro under an antiviral state induced by recombinant IFN-α1. The T217A221 reverted variant replicated to levels 23-fold higher than the T217T221 strain in IFN-α1 treated cells. Finally, reverted TA strains were virulent when tested in an in vivo trial in susceptible salmon fry. In conclusion, these results indicate that stress plays a key role in viral replication in vivo and can facilitate conditions that will allow reversion from attenuated virus variants of IPNV.

A Review of Intra- and Extracellular Antigen Delivery Systems for Virus Vaccines of Finfish

Vaccine efficacy in aquaculture has for a long time depended on evaluating relative percent survival and antibody responses after vaccination. However, current advances in vaccine immunology show that the route in which antigens are delivered into cells is deterministic of the type of adaptive immune response evoked by vaccination. Antigens delivered by the intracellular route induce MHC-I restricted CD8+ responses while antigens presented through the extracellular route activate MHC-II restricted CD4+ responses implying that the route of antigen delivery is a conduit to induction of B- or T-cell immune responses. In finfish, different antigen delivery systems have been explored that include live, DNA, inactivated whole virus, fusion protein, virus-like particles, and subunit vaccines although mechanisms linking these delivery systems to protective immunity have not been studied in detail. Hence, in this review we provide a synopsis of different strategies used to administer viral antigens via the intra- or extracellular compartments. Further, we highlight the differences in immune responses induced by antigens processed by the endogenous route compared to exogenously processed antigens. Overall, we anticipate that the synopsis put together in this review will shed insights into limitations and successes of the current vaccination strategies used in finfish vaccinology.

Immunogenicity and Cross Protective Ability of the Central VP2 Amino Acids of Infectious Pancreatic Necrosis Virus in Atlantic Salmon (Salmo salar L.)

Infectious pancreatic necrosis virus (IPNV) is a member of the family Birnaviridae that has been linked to high mortalities in juvenile salmonids and postsmolt stages of Atlantic salmon (Salmo salar L.) after transfer to seawater. IPN vaccines have been available for a long time but their efficacy has been variable. The reason for the varying immune response to these vaccines has not well defined and studies on the importance of using vaccine trains homologous to the virulent field strain has not been conclusive. In this study we prepared one vaccine identical to the virulent Norwegian Sp strain NVI-015 (NCBI: 379740) (T217A221T247 of VP2) and three other vaccine strains developed using the same genomic backbone altered by reverse genetics at three residues yielding variants, T217T221T247, P217A221A247, P217T221A247. These 4 strains, differing in these three positions only, were used as inactivated, oil-adjuvanted vaccines while two strains, T217A221T247 and P217T221A247, were used as live vaccines. The results show that these three residues of the VP2 capsid play a key role for immunogenicity of IPNV vaccines. The virulent strain for inactivated vaccines elicited the highest level of virus neutralization (VN) titers and ELISA antibodies. Interestingly, differences in immunogenicity were not reflected in differences in post challenge survival percentages (PCSP) for oil-adjuvanted, inactivated vaccines but clearly so for live vaccines (TAT and PTA). Further post challenge viral carrier state correlated inversely with VN titers at challenge for inactivated vaccines and prevalence of pathology in target organs inversely correlated with protection for live vaccines. Overall, our findings show that a few residues localized on the VP2-capsid are important for immunogenicity of IPNV vaccines.

A Review of Bovine Tuberculosis in the Kafue Basin Ecosystem

The Kafue basin ecosystem is the only remaining natural habitat for the endangered Kafue lechwe antelope (Kobus leche Kafuensis). However, hydroelectricity power production, large-scale sugar plantations, commercial fishing and increasing livestock production are threatening its natural existence and sustainability. Further, increasing human settlements within and around the Kafue basin have resulted in decreased grazing grounds for the Kafue lechwe antelopes despite a corresponding increase in cattle population sharing the same pasture. Baseline epidemiological data have persistently reported findings of bovine tuberculosis (BTB) in both wild and domestic animals, although these have been deficient in terms of describing direct evidence in the role of either lechwe antelopes or cattle in the reported observations. Despite the current literature being deficient in establishing the casual role and transmission patterns of BTB, a bimodal route of infection at the livestock/wildlife interface has been postulated. Likewise, it is not known how much of (BTB) has the potential of causing disease in humans. This paper, seeks to underline those aspects that need further research and update available data on BTB in the Kafue basin with regards to the prevalence, distribution, risk factors, threats on wildlife conservation, livestock production, public health implications, and possible mitigatory measures.

Challenges and Economic Implications in the Control of Foot and Mouth Disease in Sub-Saharan Africa: Lessons from the Zambian Experience

Foot and mouth disease is one of the worlds most important livestock diseases for trade. FMD infections are complex in nature and there are many epidemiological factors needing clarification. Key questions relate to the control challenges and economic impact of the disease for resource-poor FMD endemic countries like Zambia. A review of the control challenges and economic impact of FMD outbreaks in Zambia was made. Information was collected from peer-reviewed journals articles, conference proceedings, unpublished scientific reports, and personal communication with scientists and personal field experiences. The challenges of controlling FMD using mainly vaccination and movement control are discussed. Impacts include losses in income of over US

The effect of seasonal variation on anthrax epidemiology in the upper Zambezi floodplain of western Zambia.

1.6 billion from exports of beef and sable antelopes and an annual cost of over US

A Review of Ecological Factors Associated with the Epidemiology of Wildlife Trypanosomiasis in the Luangwa and Zambezi Valley Ecosystems of Zambia

2.7 million on preventive measures. Further impacts included unquantified losses in production and low investment in agriculture resulting in slow economic growth. FMD persistence may be a result of inadequate epidemiological understanding of the disease and ineffectiveness of the control measures that are being applied. The identified gaps may be considered in the annual appraisal of the FMD national control strategy in order to advance on the progressive control pathway.

Trypanosoma brucei Infection in asymptomatic greater Kudus (Tragelaphus strepsiceros) on a game ranch in Zambia.

Anthrax has become endemic throughout the upper Zambezi floodplain located in the Western Province of Zambia over the recent years. To date, no comprehensive study has been carried out to determine whether recurrence of anthrax outbreaks may be linked to differences in precipitation and human activities. Retrospective data for the period 1999 to 2007 showed that a total of 1,216 bovine cases of anthrax were reported. During the same period, 1,790 human anthrax cases and a corresponding case fatality rate of 4.63% (83/1,790) was documented in the upper Zambezi floodplain. Occurrence of human cases was highly correlated with cattle outbreaks (r = 0.94, p < 0.001). Differences in precipitation were significantly associated with the occurrence of anthrax outbreaks (χ2 = 4.75, p < 0.03), indicating that the likelihood of outbreaks occurring was higher during the dry months when human occupancy of the floodplain was greater compared to the flooding months when people and livestock moved out of this region. Human dependency on the floodplain was shown to significantly influence the epidemiology of anthrax in the upper Zambezi floodplain of western Zambia. Methods for mitigating anthrax outbreaks by disrupting the cycle of transmission are herein highlighted.

Sarcoptes mite epidemiology and treatment in African buffalo (Syncerus caffer) calves captured for translocation from the Kafue game management area to game ranches

Trypanosomiasis has been endemic in wildlife in Zambia for more than a century. The disease has been associated with neurological disorders in humans. Current conservation strategies by the Zambian government of turning all game reserves into state-protected National Parks (NPs) and game management areas (GMAs) have led to the expansion of the wildlife and tsetse population in the Luangwa and Zambezi valley ecosystem. This ecological niche lies in the common tsetse fly belt that harbors the highest tsetse population density in Southern Africa. Ecological factors such as climate, vegetation and rainfall found in this niche allow for a favorable interplay between wild reservoir hosts and vector tsetse flies. These ecological factors that influence the survival of a wide range of wildlife species provide adequate habitat for tsetse flies thereby supporting the coexistence of disease reservoir hosts and vector tsetse flies leading to prolonged persistence of trypanosomiasis in the area. On the other hand, increase in anthropogenic activities poses a significant threat of reducing the tsetse and wildlife habitat in the area. Herein, we demonstrate that while conservation of wildlife and biodiversity is an important preservation strategy of natural resources, it could serve as a long-term reservoir of wildlife trypanosomiasis.

De Novo Transcriptome Analysis Shows That SAV-3 Infection Upregulates Pattern Recognition Receptors of the Endosomal Toll-Like and RIG-I-Like Receptor Signaling Pathways in Macrophage/Dendritic Like TO-Cells

Trypomastogotes of Trypanosoma brucei were detected from 4 asymptomatic kudus (Tragelaphus strepsiceros) on a game ranch located approximately 45 km north east of Lusaka, Zambia. Blood smears examined from 14 wildlife species comprising of the impala (Aepyceros melampus), Kafue lechwe (kobus leche kafuensis), sable antelope (Hippotragus niger), tsessebe (Damaliscus lunatus), warthog (Phacochoerus aethiopicus), puku (Kobus vardoni), zebra (Equus burchelli), waterbuck (Kobus ellipsiprymnus), bushbuck (Tragelaphus scriptus), reedbuck (Redunca arundinum), wilderbeest (Connochaetes taurinus), hartebeest (Alcephelus lichtensteini), African buffalo (Syncerus caffer), and kudu (Tragelaphus strepsiceros) showed that only the kudu had T. brucei. Although game ranching has emerged to be a successful ex-situ conservation strategy aimed at saving the declining wildlife population in the National Parks, our findings suggest that it has the potential of aiding the re-distribution of animal diseases. Hence, there is a need for augmenting wildlife conservation with disease control strategies aimed at reducing the risk of disease transmission between wildlife and domestic animals.