Status and gaps of research on respiratory disease pathogens of swine in Africa.

Over the last two decades, the pig population in Africa has grown rapidly, reflecting the increased adoption of pig production as an important economic activity. Of all species, pigs are likely to constitute a greater share of the growth in the livestock subsector. However, constraints such as respiratory infectious diseases cause significant economic losses to the pig industry worldwide. Compared to industrialized countries, the occurrence and impacts of respiratory diseases on pig production in Africa is under-documented. Hence, knowledge on prevalence and incidence of economically important swine respiratory pathogens in pigs in Africa is necessary to guide interventions for prevention and control. The purpose of this review was to document the current status of research on five important respiratory pathogens of swine in Africa to inform future research and interventions. The pathogens included were porcine reproductive and respiratory syndrome virus (PPRSv), porcine circovirus 2 (PCV2), Mycoplasma hyopneumoniae (M. hyopneumoniae), Actinobacillus pleuropneumoniae (APP) and swine influenza A viruses (IAV). For this review, published articles were obtained using Harzing's Publish or Perish software tool from GoogleScholar. Articles were also sourced from PubMed, ScienceDirect, FAO and OIE websites. The terms used for the search were Africa, swine or porcine, respiratory pathogens, M. hyopneumoniae, APP, PCV2, PPRSv, IAV, prevention and control. In all, 146 articles found were considered relevant, and upon further screening, only 85 articles were retained for the review. The search was limited to studies published from 2000 to 2019. Of all the studies that documented occurrence of the five respiratory pathogens, most were on IAV (48.4%, n = 15), followed by PCV2 (25.8%, n = 8), PPRSv (19.4%, n = 6), while only one study (3.2%, n = 1) reported APP and M. hyopneumoniae. This review highlights knowledge and information gaps on epidemiologic aspects as well as economic impacts of the various pathogens reported in swine in Africa, which calls for further studies.

Genetic Characterization of Circulating African Swine Fever Viruses in Nigeria (2007-2015).

Sequencing and analysis of three discrete genome regions of African swine fever viruses (ASFV) from archival samples collected in 2007-2011 and active and passive surveillance between 2012 and 2015 in Nigeria were carried out. Analysis was conducted by genotyping of three single-copy African swine fever (ASF) genes. The E183L and B646L genes that encode structural proteins p54 and p72, respectively, were utilized to delineate genotypes before intragenotypic resolution by characterization of the tetrameric amino acid repeat region within the hypervariable central variable region of the B602L gene. The results showed no variation in the p72 and p54 gene regions sequenced. Phylogeny of p72 sequences revealed that all the Nigerian isolates belonged to genotype I, while that of the p54 recovered the Ia genotype. Analysis of B602L gene revealed the differences in the number of tetrameric repeats. Four new variants (Tet-15, Tet-17a, Tet-17b and Tet-48) were recovered, while a fifth variant (Tet-20) was the most widely distributed in the country displacing Tet-36 reported previously in 2003-2006. The viruses responsible for ASF outbreaks in Nigeria are from very closely related but mutated variants of the virus that have been circulating since 1997. A practical implication of the genetic variability of the Nigerian viral isolates in this study is the need for continuous sampling and analysis of circulating viruses, which will provide epidemiological information on the evolution of ASFV in the field versus new incursion for informed strategic control of the disease in the country.

Campylobacteriosis, salmonellosis, and shigellosis in free-ranging human-habituated mountain gorillas of Uganda.

For conservation purposes and due to growing ecotourism, free-ranging mountain gorillas (Gorilla gorilla beringei) have been habituated to humans. Fecal specimens (n = 62) collected in January 1999 from mountain gorillas of the Bwindi and Mgahinga National Parks, Uganda, were tested for Campylobacter spp., Salmonella spp., and Shigella spp., and the overall prevalence of infection was 19%, 13%, and 6%, respectively. The prevalence of positive specimens was not related to the year of habituation of a gorilla group to humans. Campylobacter spp., Salmonella, and Shigella spp. infections were not distributed equally among the age classes of gorillas; most of the enteropathogens (80%), and all Shigella spp. organisms, S. sonnei, S. boydii, and S. flexneri, were isolated from subadults and adult gorillas with ages ranging from 6.0 to 11.9 yr. The prevalence of Campylobacter spp. and Salmonella spp. infections among human-habituated gorillas has doubled during the last 4 yr, and isolation of Shigella spp. for the first time from mountain gorillas, may indicate enhanced anthropozoonotic transmission of these enteropathogens.

Evaluation of the adjuvant effect of Escherichia coli heat-labile enterotoxin mutant (LTK63) on the systemic immune responses to intranasally co-administered measles virus nucleoprotein. Part I: antibody responses.

The adjuvanticity and immunogenicity of the heat-labile enterotoxin (LT) of Escherichia coli and of its non-toxic mutant, LTK63, was evaluated after intranasal administration of CBA mice with recombinant measles virus nucleoprotein (rMVNP) with or without LT or LTK63. Both LT and LTK63 were shown to be highly immunogenic with higher responses observed 4 weeks after the booster immunization. Although the nucleoprotein was immunogenic on its own, mice immunized with the nucleoprotein plus wild type LT produced significantly high antibody responses (p< 0.01). Mice that received the rMVNP with LTK63 also generated strong antibody responses to rMVNP. These antibodies were also significantly higher than those of rMVNP alone (p< 0.05). No significant differences were observed between groups of mice immunized intranasally with rMVNP plus LT or LTK63 (p> 0.05). Data on IgG antibody isotype profiles showed that IgG 1 and IgG 2a were predominant in mice immunized with rMVNP + LT or LTK63 whereas IgG 1 predominated when rMVNP was given on its own implying that LT and LTK63 induce both Th1 and Th2-type immune responses. These results highlight the great potential of this non-toxic mutant of LT as a safe vaccine adjuvant.

Rapid detection of Mycobacterium avium subsp. paratuberculosis from cattle and zoo animals by nested PCR.

Paratuberculosis, caused by Mycobacterium avium subsp. paratuberculosis, a suspect causative agent of Crohn's disease in man, is an emerging disease of international proportions affecting all ruminants. Early stage detection of Mycobacterium avium subsp. paratuberculosis infection would accelerate progress in control programmes. Despite new molecular approaches the standard diagnostic test for this disease is at present still the time consuming classic isolation procedure. Therefore, alternative diagnostic tests such as PCR, are needed for quick detection of infected animals. In this study, the conventional enrichment and isolation procedure and two IS900-based PCR methods for detection of Mycobacterium avium subsp. paratuberculosis in clinical samples from zoo animals and cattle were compared. A total number of 48 different clinical specimens obtained from animals suspected of having paratuberculosis were examined. The samples included faeces (n = 15) and organ tissues (n = 33). Of the faecal specimens two were identified as positive by nested PCR, whereas none was positive by single PCR or by culture. 28 organ specimens were found positive by culture. Mycobacterium avium subsp. paratuberculosis DNA was detected by nested PCR in 82% of the organ specimens identified positive by culture (23 samples) as opposed to 57% by single PCR (16 samples). Nested PCR also identified two positive samples that were not detected by either culture or single PCR. These findings show the great potential of nested PCR as a useful tool for the rapid diagnosis of paratuberculosis in animals.

Evaluation of the LTK63 adjuvant effect on cellular immune responses to measles virus nucleoprotein.

BACKGROUND: A lot of pathogens enter the body via the nasal route. The construction of non-toxic mutants of heat labile Escherichia coli enterotoxin (LT), which is a potent mucosal adjuvant, represents a major breakthrough for the development of mucosal vaccines. OBJECTIVE: This study was undertaken to critically evaluate the adjuvanticity of the mutant of LT (LTK63) on the cellular immune responses to intranasally co-administered recombinant measles virus nucleoprotein (rMVNP). METHODS: Groups of CBA mice were immunized intranasally with rMVNP with or without LT or LTK63 as adjuvants. Another group was immunized subcutaneously with rMVNP in Freund's adjuvant. rMVNP and measles virus (MV) were used in a proliferation assay to test the LTK63 potentiating ability to induce T cell responses. Subsequently MVNP synthetic peptides spanning the length of the N protein were used with a proliferation assay to identify the T cell epitopes. RESULTS: Splenocytes from mice immunized intranasally with rMVNP plus LT or LTK63, showed strong dose dependent proliferative responses to both the MVNP and MV. However, proliferative responses from the latter group were significantly lower than the former group (P < 0.05). Splenocytes tested recognized peptides 20, 21, 28, 31, 39, 40 and 50, suggesting these to be among important epitopes. Subcutaneous route was not effective in priming for T cell responses to rMVNP. CONCLUSION: These data further demonstrate the great potential of LTK63 as a safe mucosal vaccine adjuvant.

Comparison of the effects of different nutrient media on production of heat-stable enterotoxin-b by Escherichia coli.

Trypticase soy broth (TSB) has been commonly used to culture Escherichia coli strains for detection or harvest of heat-stable enterotoxin-b (STb); however, in our experience, the yields have been low. In this study, we compared STb yields resulting from growth in brain heart infusion broth (BHI) supplemented with 2% casamino acids (BHI-CA) with that from TSB. Since strains may concurrently express heat-labile enterotoxin (LT) and lincomycin has been reported to cause increased expression of LT, we also compared its effects on STb production. STb(+) clones had significantly higher production of STb when grown in BHI-CA compared to TSB, based on enzyme-linked immunosorbent assay (ELISA) conducted on cell-free supernatants. The superiority of BHI-CA to TSB was further tested on 17 porcine enterotoxigenic E. coli (ETEC) isolates, all positive for the STb gene (estB) by PCR. Cell-free supernatants of 100% of the ETEC isolates were detectably positive for STb by ELISA when grown in BHI-CA, in contrast to only 10 strains positive (59%) when TSB supernatants were analyzed. For all the samples, the amounts of STb expressed in BHI-CA based on ELISA were significantly higher than those from TSB (p

Immune responses and protection induced by mucosal and systemic immunisation with recombinant measles nucleoprotein in a mouse model of measles virus-induced encephalitis.

In this study the immunogenicity of recombinant nucleoprotein (Np) administered intranasally or intraperitoneally, and its ability to support a systemic protective anti-virus antibody response was examined, in a mouse model of measles virus (MV)-induced encephalitis. Although both intranasal and intraperitoneal routes of immunisation resulted in priming Np- and MV-specific T-cell responses, the intraperitoneal route was shown to prime for a predominantly IgG2a serum anti-MV antibody response of high avidity, which confered complete protection following intracranial challenge with a neuroadapted strain of MV. On the other hand, intranasal priming resulted in a mixed IgG1, IgG2a serum anti-MV antibody response of low avidity, and only 43% of immunised mice survived following intracranial challenge with the neuroadapted strain of MV. These findings suggest that the route of immunisation in combination with an appropriate adjuvant could influence the induction of a quality antibody response with protective capacity.