Francis Dziva - Academia.edu (original) (raw)

Papers by Francis Dziva

Advances in Infectious Diseases, 2016

American Journal of Experimental Agriculture, 2016

Veterinary Microbiology, Oct 1, 2001

Eighty-one isolates presumptively identi®ed as Pasteurella multocida from a variety of diseases i... more Eighty-one isolates presumptively identi®ed as Pasteurella multocida from a variety of diseases in animals in Zimbabwe were subjected to biochemical characterization, capsular typing and RAPD analysis. The majority of isolates (over 80%) were assigned into named taxa and were predominantly P. multocida subsp. multocida and P. multocida subsp. septica, whilst the remainder were unassigned. Serogroup A was predominant among the three capsular types (A, B and D) of P. multocida detected. Three main RAPD clusters and three subclusters were observed among the majority of isolates (93.8%), whilst the remainder was found to be weakly related. Nine different groups of strains with similar RAPD pro®les (100% similarity) were also observed. The reference strain of capsular serogroup F clustered with the reference strain of P. multocida subsp. septica, whilst all other serogroups clustered with reference strains of subsp. multocida and gallicida. Notably, serogroups A and D were observed to be closely related to the reference strain of subsp. multocida. The relationship between biotype, capsular type, host origin and disease manifestation was not clear-cut. However, most pig isolates of subsp. multocida clustered together as did most cattle isolates of subsp. multocida. RAPD tended to separate subsp. multocida from septica. #

Infection ecology & epidemiology, 2015

Otitis externa is a common inflammatory ear disease in dogs caused by a variety of pathogens, and... more Otitis externa is a common inflammatory ear disease in dogs caused by a variety of pathogens, and coagulase-positive staphylococci are frequently isolated from such infections. To identify antimicrobial susceptibility profiles and methicillin-resistant strains among coagulase-positive staphylococci isolated from otitis externa in dogs. A cross-sectional study was performed over 2 years on 114 client-owned dogs presented to the Veterinary Teaching Hospital with a primary complaint of ear infections. Swabs were obtained from both ears and cultured for staphylococci which were subsequently confirmed as coagulase-positive using rabbit plasma. Antimicrobial susceptibility assays were assessed on all isolates followed by subsequent genetic analysis for species identification and detection of the mecA gene. Sixty-five coagulase-positive staphylococci were isolated from 114 client-owned dogs. The isolates exhibited resistance against neomycin (58.5%), streptomycin (49.2%), penicillin (49.2%...

Microbiology, Dec 1, 2002

Http Dx Doi Org 10 1080 03079450802216652, Jul 14, 2008

Avian colibacillosis is caused by a group of pathogens designated avian pathogenic Escherichia co... more Avian colibacillosis is caused by a group of pathogens designated avian pathogenic Escherichia coli (APEC). Despite being known for over a century, avian colibacillosis remains one of the major endemic diseases afflicting the poultry industry worldwide. Autologous bacterins provide limited serotype-specific protection, yet multiple serogroups are associated with disease, especially O1, O2 and O78 among many others. Experimental infection models have facilitated the identification of some key APEC virulence genes and have allowed testing of vaccine candidates. Well-recognized virulence factors include Type 1 (F1) and P (Pap/Prs) fimbriae for colonization, IbeA for invasion, iron acquisition systems, TraT and Iss for serum survival, K and O antigens for anti-phagocytic activity, and a temperature-sensitive haemagglutinin of imprecise function. Intriguingly, these factors do not occur universally among APEC, suggesting the presence of multiple alternative mechanisms mediating pathogenicity. The recent availability of the first complete APEC genome sequence can be expected to accelerate the identification of bacterial genes expressed during infection and required for virulence. High-throughput molecular approaches like signature-tagged transposon mutagenesis have already proved invaluable in revealing portfolios of genes expressed by pathogenic bacteria during infection, and this has enabled identification of APEC O2 factors required for septicaemia in the chicken model. Complimentary approaches, such as in vivo-induced antigen technology, exist to define the activities of APEC in vivo. In recent years, reverse vaccinology and immuno-proteomic approaches have also enabled identification of novel vaccine candidates in other bacterial pathogens. Collectively, such information provides the basis for the development or improvement of strategies to control APEC infections in the food-producing avian species.

Clinical Infectious Diseases, 2015

Nontyphoidal salmonellosis continues to pose a global threat to human health, primarily by causin... more Nontyphoidal salmonellosis continues to pose a global threat to human health, primarily by causing food-borne illnesses, and food-producing animals are the principal reservoirs of many pathogenic serovars. To identify key control points and generate information that may enable future estimation of the transmission routes between the environment, animals, and humans, we examined data on Salmonella isolates in South Africa. Samples were obtained from livestock and poultry on farms, meat at abattoirs, raw materials at feed mills, animal feed, and environmental sources (eg, poultry houses, abattoirs, feed mills, water) from 2012 to 2014 in compliance with each establishment&amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s protocols conforming to International Organization for Standardization (ISO) (ISO/TS 17728, ISO 18593:2004 and ISO 17604:2003) standards. Isolation and serotyping of Salmonella were performed according to the scope of accreditation of the respective laboratories conforming to ISO/IEC 17025:2005 standard techniques. Salmonella was isolated from 9031 of 180 298 (5.0%) samples, and these isolates were distributed among 188 different serovars. Salmonella Enteritidis was the most frequent isolate, with 1944 of 180 298 (21.5%) originating from poultry on farms, poultry meat, and poultry houses, followed by Salmonella Havana, with 677 of 180 298 (7.5%), mostly from environmental samples. Serovars that are uncommonly associated with human disease (Salmonella Idikan, Salmonella Salford, and Salmonella Brancaster) were isolated at higher frequencies than Salmonella Typhimurium, a common cause of human illness. Environmental samples accounted for 3869 of 9031 (42.8%) samples positive for Salmonella. We describe the frequent isolation of Salmonella of a wide variety of serovars, from an array of animal feeds, food animals, and food animal environment. As prevention of human salmonellosis requires the effective control of Salmonella in food animals, these data can be used to facilitate Salmonella control in food animals and thereby prevent human infections.

Vaccine, Jan 15, 2015

Avian pathogenic Escherichia coli (APEC) exert substantial economic costs on poultry producers wo... more Avian pathogenic Escherichia coli (APEC) exert substantial economic costs on poultry producers worldwide. Vaccination is an attractive method of control, but the immunological basis of protection is poorly understood. Here, we examine the effect of intramuscular injection of cyclophosphamide or saline on homologous protection induced by licensed inactivated or live-attenuated APEC O78 vaccines in chickens. In saline-treated birds, both vaccines induced significant APEC-specific IgY and protection against homologous challenge, as evidenced by enumeration of tissue-associated bacteria and analysis of pathology. In cyclophosphamide-treated birds, B cells were severely depleted whereas percentages of circulating CD4- and CD8-positive T cells were normal as detected by flow cytometry. Further, such birds did not produce APEC-specific IgY and were as susceptible to challenge as age-matched unvaccinated controls. The data indicate that homologous protection conferred by licensed APEC vacci...

Veterinary Microbiology, 2008

Please cite this article as: Dziva, F., Muhairwa, A., Bisgaard, M., Christensen, H., Diagnostic a... more Please cite this article as: Dziva, F., Muhairwa, A., Bisgaard, M., Christensen, H., Diagnostic and typing options for investigating diseases associated with Pasteurella multocida, Veterinary Microbiology (2007), Abstract 1 2 Pasteurella multocida is responsible for major animal diseases of economic 3 significance in both developed and developing countries whereas human infections 4 related to this bacterium are infrequent. Significantly, development of a carrier status 5 or latent infections plays a critical role in the epidemiology of these diseases. Aiming 6 at increased knowledge of these infections, we examine potential diagnostic and 7 selected typing systems for investigating diseases caused by P. multocida. Detection 8 of P. multocida from clinical specimen by; i) isolation and identification, ii) 9 polymerase chain reaction (PCR), iii) specific hybridisation probes, iv) serological 10 tests and v) other alternative methods is critically evaluated. These detection systems 11 provide a wide spectrum of options for rapid diagnosis and for detecting and 12 understanding of latent infections in herd/flock health control programmes, though 13 PCR methods for detecting P. multocida in clinical specimen appear increasingly 14 preferred. For establishing the clonality of outbreak strains, we select to discuss 15 macromolecular profiling, serotyping, biotyping, restriction enzyme analysis, 16 ribotyping and multiplex PCR typing. Although P. multocida infections can be 17 rapidly diagnosed with molecular and serological tests, isolation and accurate species 18 identification are central to epidemiological tracing of outbreak strains. Our review 19

Veterinary Microbiology, 2001

Microbiology (Reading, England), 2002

Veterinary Research, 2015

Avian pathogenic Escherichia coli (APEC) infections are a serious impediment to sustainable poult... more Avian pathogenic Escherichia coli (APEC) infections are a serious impediment to sustainable poultry production worldwide. Licensed vaccines are available, but the immunological basis of protection is ill-defined and a need exists to extend cross-serotype efficacy. Here, we analysed innate and adaptive responses induced by commercial vaccines in turkeys. Both a live-attenuated APEC O78 ΔaroA vaccine (Poulvac® E. coli) and a formalin-inactivated APEC O78 bacterin conferred significant protection against homologous intra-airsac challenge in a model of acute colibacillosis. Analysis of expression levels of signature cytokine mRNAs indicated that both vaccines induced a predominantly Th2 response in the spleen. Both vaccines resulted in increased levels of serum O78-specific IgY detected by ELISA and significant splenocyte recall responses to soluble APEC antigens at post-vaccination and post-challenge periods. Supplementing a non-adjuvanted inactivated vaccine with Th2-biasing (Titermax® Gold or aluminium hydroxide) or Th1-biasing (CASAC or CpG motifs) adjuvants, suggested that Th2-biasing adjuvants may give more protection. However, all adjuvants tested augmented humoral responses and protection relative to controls. Our data highlight the importance of both cell-mediated and antibody responses in APEC vaccine-mediated protection toward the control of a key avian endemic disease.

Enterohaemorrhagic Escherichia coli (EHEC) comprise an important group of zoonotic enteric pathog... more Enterohaemorrhagic Escherichia coli (EHEC) comprise an important group of zoonotic enteric pathogens. In humans, some EHEC infections result in bloody or non- bloody diarrhoea, which may be complicated by haem- orrhagic colitis and severe renal and neurological sequelae, including haemolytic uraemic syndrome (HUS). Ruminants are an important reservoir of EHEC and human infections are frequently associated with direct or indirect

Infection Ecology & Epidemiology, 2012

Zoonoses, which account for approximately 75% of emerging human infectious diseases worldwide, po... more Zoonoses, which account for approximately 75% of emerging human infectious diseases worldwide, pose a re-emerging threat to public health. With an ever-increasing interrelationship between humans, livestock and wildlife species, the threat to human health will rise to unprecedented levels. Wildlife species contribute to the majority of emerging diseases; therefore, there is an urgent need to define control systems of zoonoses of wildlife origin but very little information exists. In this review, we examine prevalent zoonotic infections reported in Namibia between 1990 and 2009 and assess their potential impact on the growing wildlife industry. A wide spectrum of zoonotic diseases was confirmed in both livestock and wildlife species, with rabies and anthrax cases being over-represented and also showing the widest species distribution. Whilst vaccination and ante-mortem inspection against these diseases may curb infected livestock species from entering the human food chain, such practices are difficult to implement in free-ranging wildlife species. In this context, there is a need to improve existing control measures and/or develop novel and better interventional strategies to reduce the threat of this re-emerging global problem. This review provides the basis for initiating a multidisciplinary evidence-based approach to control zoonoses in countries with thriving wildlife and game farming.

Veterinary Research, 2014

Avian pathogenic Escherichia coli (APEC) cause severe respiratory and systemic disease in poultry... more Avian pathogenic Escherichia coli (APEC) cause severe respiratory and systemic disease in poultry yet the nature and consequences of host immune responses to infection are poorly understood. Here, we describe a turkey sub-acute respiratory challenge model and cytokine, cell-mediated and humoral responses associated with protection against homologous re-challenge. Intra-airsac inoculation of turkeys with 10 5 colony-forming units of APEC O78:H9 strain χ7122nal R induced transient and mild clinical signs of colibacillosis followed by clearance of the bacteria from the lungs and visceral organs. Upon re-challenge with 10 7 χ7122nal R , primed birds were solidly protected against clinical signs and exhibited negligible bacterial loads in visceral organs, whereas age-matched control birds exhibited high lesion scores and bacterial loads in the organs. Levels of mRNA for signature cytokines suggested induction of a Th1 response in the lung, whereas a distinct anti-inflammatory cytokine profile was detected in the liver. Proliferative responses of splenocytes to either Concanavalin A or soluble χ7122nal R antigens were negligible prior to clearance of bacteria, but APEC-specific responses were significantly elevated at later time intervals and at re-challenge relative to control birds. Primary infection also induced significantly elevated χ7122nal R -specific serum IgY and bile IgA responses which were bactericidal against χ7122nal R and an isogenic Δrfb mutant. Bactericidal activity was observed in the presence of immune, but not heat-inactivated immune serum, indicating that the antibodies can fix complement and are not directed solely at the lipopolysaccharide O-antigen. Such data inform the rational design of strategies to control a recalcitrant endemic disease of poultry.

Veterinary Microbiology, 2004

Atrophic rhinitis in pigs is rarely reported in Southern Africa. To determine the relationship be... more Atrophic rhinitis in pigs is rarely reported in Southern Africa. To determine the relationship between Pasteurella multocida clones from clinical cases of atrophic rhinitis, twenty-one strains were characterised by selected phenotypic and genotypic methods. Biochemical analysis classified 18 strains as P. multocida subspecies multocida, whilst the remainder were grouped into separate unassigned biotypes. Capsular groups A (16/21) and D (l/21) were found among the isolates by PCR. Four ribotype patterns were obtained following HpaII ribotyping, whilst random amplification of polymorphic DNA (RAPD) revealed three main clusters. However, subclusters were also noted for each RAPD cluster. Our results indicate that RAPD offers a better discrimination of strains than ribotyping and that none of the phenotypic characters were directly related to the genotypic clusters.

Veterinary Microbiology, 2007

Veterinary Immunology and Immunopathology, 2007

Enterohaemorrhagic Escherichia coli (EHEC) infections in humans are an important public health co... more Enterohaemorrhagic Escherichia coli (EHEC) infections in humans are an important public health concern and are commonly acquired via contact with ruminant faeces. Cattle are a key control point however cross-protective vaccines for the control of EHEC in the bovine reservoir do not yet exist. The EHEC serogroups that are predominantly associated with human infection in Europe and North America are O157 and O26. Intimin and EHEC factor for adherence (Efa-1) play important roles in intestinal colonisation of cattle by EHEC and are thus attractive candidates for the development of subunit vaccines. Immunisation of calves with the cell-binding domain of intimin subtypes β or γ via the intramuscular route induced antigen-specific serum IgG1 and, in some cases salivary IgA responses, but did not reduce the magnitude or duration of faecal excretion of EHEC O26:H-(Int 280 -β) or EHEC O157:H7 (Int 280 -γ) upon subsequent experimental challenge. Similarly, immunisation of calves via the intramuscular route with the truncated Efa-1 protein (Efa-1′) from EHEC O157:H7 or a mixture of the amino-terminal and central thirds of the full-length protein (Efa-1-N and M) did not protect against intestinal colonisation by EHEC O157:H7 (Efa-1′) or EHEC O26:H-(Efa-1-N and M) despite the induction of humoral immunity. A portion of the serum IgG1 elicited by the truncated recombinant antigens in calves was confirmed to recognise native protein exposed on the bacterial surface. Calves immunised with a mixture of Int 280 -γ and Efa-1′ or an EHEC O157:H7 bacterin via the intramuscular route then boosted via the intranasal route with the same antigens using cholera toxin B subunit as an adjuvant were also not protected against intestinal colonisation by EHEC O157:H7. These studies highlight the need for further studies to develop and test novel vaccines or treatments for control of this important foodborne pathogen.

Journal of the South African Veterinary Association, 2013

CITATION 1 READS 25 5 authors, including: Some of the authors of this publication are also workin... more CITATION 1 READS 25 5 authors, including: Some of the authors of this publication are also working on these related projects: please visit my webpage to see what research we are involved in at the moment at www0.sun.ac.za/sarchi View project Kuda Magwedere South Africa Government