Abstract
The autovaccine was produced in-house using a bacterial isolate from a diseased fish from the target farm. Three groups of 150 fish each were injected with either 1) an oil-adjuvanted, inactivated whole cell autovaccine, 2) adjuvant only or 3) PBS (negative control). Approximately 660 degree days post vaccination, the fish were challenged with 9x105 cfu bacteria/fish by intraperitoneal injection and monitored for a further 28 days. Protection against infections was measured by lack of/reduced bacterial loads both by bacterial re-isolation and immunohistochemistry as well as absence of clinical signs/pathology. Significantly less L. garvieae (p<0.03) was re-isolated from either the adjuvant only or control groups compared to the vaccinated group. Furthermore, a significantly high amount (p<0.001) of anti-L. garvieae specific antibodies were observed in the vaccinated group compared to the adjuvant only or control groups at time of challenge. This coincided with protection against infection measured by absence/reduced L. garvieae re-isolation from internal organs, reduced clinical signs and lack of pathology in this group. In the adjuvant only and control groups, bacteria were re-isolated from the kidney, liver, spleen, brain and eyes during the first 14 days. The findings suggest that oil-based vaccines can protect tilapia against L. garvieae infection through an antibody mediated response.
Highlights
Tilapia farming in Zambia is a relatively young but rapidly growing industry
The findings suggest that oil-based vaccines can protect tilapia against L. garvieae infection through an antibody mediated response
The results showed that control fish were infected first (3 dpc) followed by the adjuvant only and vaccinated groups from which bacteria was re-isolated at 5 dpi
Summary
Commercialization started as far back as the 1990s, the surge in production was not until 2010 that cage-based commercial farming intensified on Lake Kariba [1]. As with intensive fish farming elsewhere that is affected by fish diseases [3], the increase in the fish production on Lake Kariba soon faced the same problem. Lactococcus garvieae is a facultatively anaerobic, non-motile, non-spore forming, Grampositive, ovoid cocci bacteria belonging to the Phylum Firmicutes, Family Streptococcaceae, Order Lactobacilles and genus Lactococcus. It is well-known for infecting and causing disease in rainbow trout [5, 6] and yellowtail (Seriola quinqueradiata) [7].
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