Detection of tilapia lake virus (TiLV) infection by PCR in farmed and wild Nile tilapia (Oreochromis niloticus) from Lake Victoria

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.

Taenia spp. infections in wildlife in the Bangweulu and Kafue flood plains ecosystems of Zambia

Taenia spp. have an indirect life cycle, cycling between a definitive and an intermediate host with zoonotic species causing public health problems in many developing countries. During the course of 2 separate surveys in Zambia (2004 and 2009), the presence of Taenia larval stages (cysticerci) was examined in Kafue lechwe (Kobus leche kafuensis), Black lechwe (Kobus leche smithermani) and other wildlife species from the Kafue and Bangweulu flood plains. Examinations involved post-mortem inspection and serum specific antigen detection. The recovered cysts from seven carcasses were characterised using PCR and DNA sequence analysis. The overall proportion of infection in wildlife on post-mortem examination was 19.0% (95% CI: 9.1-29.0%). The proportion of infected wildlife based on post-mortem examinations in the Kafue flood plains was estimated at 28.6% (95% CI: 13.3-43.9%), while the seroprevalence was estimated at 25.0% (95% CI: 2.9-47.1%). The seroprevalence for cattle in the Kafue flood plains was estimated at 61.5% (95% CI: 42.0-81.0%) while that of Kafue lechwe in the same ecosystem was estimated at 66.6% (95% CI: 45.6-85.7%). Infection rates were higher in Kafue lechwe than in Black lechwe suggesting differences in the exposure patterns. The sequencing results indicated that none of the recovered cysts were either Taenia solium or Taenia saginata. We therefore conclude they most likely belong to a less studied (wildlife) Taenia species that requires further characterisation.

Genomic sequence of an infectious bursal disease virus isolate from Zambia: classical attenuated segment B reassortment in nature with existing very virulent segment A

We determined the complete nucleotide sequence of an infectious bursal disease (IBD) virus (IBDV) isolate (designated KZC-104) from a confirmed IBD outbreak in Lusaka in 2004. The genome consisted of 3,074 and 2,651 nucleotides in the coding regions of segments A and B, respectively. Alignment of both nucleotide and deduced amino acid sequences and phylogenetic analysis revealed that the genome segment A of KZC-104 was derived from a very virulent (VV) strain, whereas its segment B was derived from a classical attenuated strain. On BLAST search, the full-length segment A and B sequences showed 98 % nucleotide sequence identity to the VV strain D6948 and 99.8 % nucleotide sequence identity to the classical attenuated strain D78. This is a unique IBDV reassortant strain that has emerged in nature, involving segment B of a cell-culture-adapted attenuated vaccine.

Quantification of chicken anaemia virus by competitive polymerase chain reaction

A quantitative method for chicken anaemia virus (CAV) was developed using competitive polymerase chain reaction (PCR). Competitive template was constructed by deletion of 33 nucleotides from a wildtype DNA clone of CAV. Quantification of CAV DNA molecules by the competitive PCR was rapid and highly reproducible when compared with conventional infectivity titration methods. The ratios of the viral DNA molecules and infectivity titres in MDCC-MSB1 cells varied between 1.3 and 3.55 log(10) among several isolates, suggesting the existence of different infection efficiencies to MDCC-MSB1 cells by isolates. The competitive PCR will be useful for studying CAV infection in vivo and/or in vitro.

Bovine clostridial infections in Zambia (1985-1994)

Retrospective surveillance study of clostridial infections of cattle in Zambia, for the period 1985 to 1994, showed that out of the 318 cases observed, 62.8% and 24.2% were from Western and Southern provinces, respectively. Of the 6 clostridia species identified, Clostridium septicum (38.1%) followed by C. chauvoei (36.2%) and C. perfringens (13.2%) were dominant. Although the highest incidence for clostridial infections was in 1989 (75 cases) and 1990 (77 cases), the number of C. perfringens cases seemed to increase. More cases were found in the dry season until the onset of the rains, that is, the period August to December.