Tilapia lake virus disease (TiLVD) has emerged to be an important viral disease of farmed Nile tilapia (Oreochromis niloticus) having the potential to impede expansion of aquaculture production. There is a need for rapid diagnostic tools to identify infected fish to limit the spread in individual farms. We report the first detection of TiLV infection by PCR in farmed and wild Nile tilapia from Lake Victoria. There was no difference in prevalence between farmed and wild fish samples (p = .65), and of the 442 samples examined from 191 fish, 28 were positive for TiLV by PCR. In terms of tissue distribution, the head kidney (7.69%, N = 65) and spleen (10.99%, N = 191), samples had the highest prevalence (p < .0028) followed by heart samples (3.45%, N = 29). Conversely, the prevalence was low in the liver (0.71%, N = 140) and absent in brain samples (0.0%, N = 17), which have previously been shown to be target organs during acute infections. Phylogenetic analysis showed homology between our sequences and those from recent outbreaks in Israel and Thailand. Given that these findings were based on nucleic acid detection by PCR, future studies should seek to isolate the virus from fish in Lake Victoria and show its ability to cause disease and virulence in susceptible fish.

The oral route offers the most attractive approach of immunization of fish for a number of reasons: the ease of administration of antigens, it is less stressful than parenteral delivery and in principle, it is applicable to small and large sized fish; it also provides a procedure for oral boosting during grow-out periods in cages or ponds. There are, however, not many commercial vaccines available at the moment due to lack of efficacy and challenges associated with production of large quantities of antigens. These are required to stimulate an effective immune response locally and systemically, and need to be protected against degradation before they reach the sites where immune induction occurs. The hostile stomach environment is believed to be particularly important with regard to degradation of antigens in certain species. There is also a poor understanding about the requirements for proper immune induction following oral administration on one side, and the potential for induction of tolerance on the other. To what extent primary immunization via the oral route will elicit both local and systemic responses is not understood in detail. Furthermore, to what extent parenteral delivery will protect mucosal/gut surfaces and vice-versa is also not fully understood. We review the work that has been done on the subject and discuss it in light of recent advances that include mass production of antigens, including the use of plant systems. Different encapsulation techniques that have been developed in the quest to protect antigens against digestive degradation, as well as to target them for appropriate immune induction are also highlighted.

BackgroundAwareness of bovine tuberculosis (BTB) by cattle owners is of extreme importance to policy makers when considering mitigation. However, to our knowledge, little is known on cattle owners' awareness of BTB in Zambia. Similarly, such knowledge is uncommon within and outside Africa. The current study investigates the epidemiological characteristics of BTB in Zambian cattle in relation to awareness by cattle owners in high and low cattle BTB prevalence settings. A cross sectional study was designed and data was gathered based on 106 cattle owners and cattle herds; subjected to an interviewer-administered questionnaire and comparative intradermal tuberculin test using a cut-off for positivity of 4 mm, respectively.ResultsReported levels of cattle and wildlife contact by respondents was at 40%, 58.2% and 1.8%, were relatively proportional to herd level prevalence of cattle BTB at 64.8%, 58.1% and 5.9% in Blue lagoon, Lochinvar and Kazungula respectively. Although 42/106 (39.6%) of cattle owners had heard of BTB, only 3 (7%) had an idea on how the disease was spread. Cattle contact with wildlife was associated with high levels of awareness by cattle owners (χ2 = 43.5, df = 2, P < 0.001). Awareness of BTB in low prevalence settings was lower compared to high prevalence settings.ConclusionsOur study has revealed low levels of awareness among cattle owners on BTB. These results could be useful for policy makers when planning mitigation measures to consider awareness levels by cattle owners for effective implementation. Such information is useful for determining sensitisation programs for cattle owners before mitigation. These results further provide useful insights that disease control is a multi-factorial process with cattle owners as an integral part that can support policy implementation.

An enduring challenge in the vaccinology of infectious pancreatic necrosis virus (IPNV) is the lack of correlation between neutralizing antibodies and protection against mortality. To better understand the immunological basis of vaccine protection, an efficacy trial including Atlantic salmon (Salmo salar L.) vaccinated with a high antigen (HiAg) or low antigen (LoAg) dose vaccine was carried out in a cohabitation challenge model using the highly virulent Norwegian Sp strain NVI015. To pinpoint the immunological basis of vaccine protection, pathogenic mechanisms of IPNV were unraveled in control fish while obtaining feedback on mechanisms of protection in the vaccinated fish. During the incubation period, infection rates were highest in control fish, followed by the LoAg group with the lowest infections being in the HiAg group. Although both the liver and pancreas are target organs prone to tissue damage, infection in the liver was delayed until acute infection in most fish. A correlate of pathology determined as the cutoff threshold of viral copy numbers linked to tissue damage in target organs was estimated at ≥ 107.0, which corresponded with an increase in mortality. The kinetics of IFNα and Mx expression suggests that these genes can be used as biomarkers of IPNV infection progression. Mechanisms of vaccine protection involved reducing infection rates, preventing infection of the liver and reducing virus replication in target organs to levels below the correlate of pathology. Overall, the study shows that antigen dose corresponds with vaccine efficacy and that antibody levels can be used as a signature of protective immunity against pathological disease and mortality.

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.

African swine fever (ASF) is a highly contagious and deadly viral hemorrhagic disease of swine. In Zambia, ASF was first reported in 1912 in Eastern Province and is currently believed to be endemic in that province only. Strict quarantine measures implemented at the Luangwa River Bridge, the only surface outlet from Eastern Province, appeared to be successful in restricting the disease. However, in 1989, an outbreak occurred for the first time outside the endemic province. Sporadic outbreaks have since occurred almost throughout the country. These events have brought into acute focus our limited understanding of the epidemiology of ASF in Zambia. Here, we review the epidemiology of the disease in areas considered nonendemic from 1989 to 2015. Comprehensive sequence analysis conducted on genetic data of ASF viruses (ASFVs) detected in domestic pigs revealed that p72 genotypes I, II, VIII and XIV have been involved in causing ASF outbreaks in swine during the study period. With the exception of the 1989 outbreak, we found no concrete evidence of dissemination of ASFVs from Eastern Province to other parts of the country. Our analyses revealed a complex epidemiology of the disease with a possibility of sylvatic cycle involvement. Trade and/or movement of pigs and their products, both within and across international borders, appear to have been the major factor in ASFV dissemination. Since ASFVs with the potential to cause countrywide and possibly regional outbreaks, could emerge from “nonendemic regions”, the current ASF control policy in Zambia requires a dramatic shift to ensure a more sustainable pig industry.

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