Research Articles (Veterinary Tropical Diseases)

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Bacterial blood microbiome of Mastomys rodents : implications for disease spill-over at the animal-human interface within the Bushbuckridge-East community, South Africa
(Frontiers Media, 2025-02) Kolo, Agatha Onyemowo; Brayton, Kelly A.; Collins, Nicola E.; Bastos, Armanda D.S.; Matthee, Sonja; Gall, Cory A.; Wentzel, Jeanette Maria; Neves, L.C.B.G.D. (Luís); Oosthuizen, Marinda C.
The Bushbuckridge-East community in Mpumalanga Province, South Africa is bordered by nature reserves, including the Manyeleti Game Reserve. Murid rodents are prevalent in both Manyeleti and communal rangelands adjoining the community households. Although rodents are reservoir hosts for a broad range of viral, bacterial and parasitic pathogens, the rodent microbial diversity and transmission of zoonotic agents to humans in the community is understudied. In this study we investigated bacterial diversity in wild and commensal rodents sampled from different habitats. The 16S rRNA gene was amplified from DNA extracted from the blood of 24 wild Mastomys and one Steatomys sp. and subjected to PacBio circular consensus sequencing. As Bartonella species were dominant in the blood microbiome, gltA gene characterization was performed to delineate species. Rodents sampled from peri-urban and communal rangelands had higher proportions of Bartonella spp. [Hlalakahle (77.7%), Gottenburg (47.8%), Tlhavekisa (83.8%)] compared to those from the protected habitat (43.8%). Ehrlichia spp., Anaplasma spp., and Coxiella burnetii were detected at <1% of the sequence reads. Conventional PCR and sequencing validated the detection of Bartonella spp. with the first confirmation of Bartonella mastomydis infection in Mastomys in South Africa. Additionally, 317 mites, 90 fleas, 10 ticks and eight lice were collected from the rodents, providing evidence of possible vectors of the organisms detected. The detection of zoonotic agents in rodents in Bushbuckridge-East community, together with prior serological confirmation of Bartonella and Coxiella in non-malarial acute febrile patients from this community, highlights the possible risks that commensal rodents pose to human health.
Phylogenomics of Brucella abortus isolated from African buffalo in Kruger National Park : new perspectives on wildlife-cattle disease dynamics
(Elsevier, 2025-05) Cossu, Carlo Andrea; Garofolo, Giuliano; Janowicz, Anna; De Massis, Fabrizio; Wentzel, Jeanette Maria; Ledwaba, Maphuti Betty; Sabeta, Claude; De Klerk, Lin-Mari; Godfroid, Jacques; Vergnaud, Gilles; Van Heerden, Henriette; ca.cossu@tuks.co.za
In South Africa, Brucella abortus biovar 1 is the primary cause of bovine brucellosis, significantly impacting cattle production and trade. Serological studies have revealed brucellosis in African wildlife, complicating control efforts due to limited epidemiological data. In 1977, B. abortus biovar 1 was isolated from an African buffalo fetus in Kruger National Park (KNP), raising speculation that buffalo may serve as reservoir hosts. This study investigated Brucella spp. in free-ranging buffalo in KNP using serological, molecular, and bacteriological methods. Brucella abortus bv 1 was isolated from lymph nodes and spleens of three sub-adult buffalo in 2022, marking the first documented recurrence in 50 years. Phylogenomic analyses revealed connections between buffalo isolates and cattle strains from South Africa and South America, suggesting spillover and shared origins from Europe. Further genomic and epidemiological surveillance is required to clarify the role of buffalo as reservoir hosts for brucellosis.
Preslaughter practices, pork physicochemical attributes and fatty acid profiles of pigs raised and slaughtered on smallholder urban farms in the Cape Metropole, South Africa
(Elsevier, 2025-06) Mathobela, Rebecca M.; Chikwanha, Obert C.; Katiyatiya, Chenaimoyo L.F.; Semwogerere, Farouk; Molotsi, Annelin H.; Marufu, Munyaradzi Christopher; Strydom, Phillip E.; Mapiye, Cletos
Pre-slaughter practices, pork physicochemical quality, and fatty acid (FA) composition of 36 Landrace barrows aged six months, sourced from five smallholder urban farms (SUFs) in low-income, high-density suburbs and one commercial abattoir in Cape Metropole District, South Africa were evaluated. Pigs on SUFs were fed three diets: (1) kitchen-bakery-vegetable waste-based, (2) bakery-dairy waste-based, or (3) homemade grain-based, while those on a large-scale farm were fed a commercial diet. Pigs on SUFs were either stunned mechanically or not stunned before slaughter. The SUFs either practiced throat or cervical spine sticking during slaughter. Carcasses from pigs fed the homemade grain-based diet had higher (P ≤ 0.05) weights, ash subcutaneous and intramuscular fat (IMF) values than those fed the other diets. The homemade grain-based diet, throat sticking treatment produced pork with the highest pH45 followed by the bakery-dairy waste-based diet, throat sticking and kitchen-bakery-vegetable waste-based diet, cervical spine treatments (P ≤ 0.05). Pigs fed a commercial diet and slaughtered by throat sticking produced pork with the lower (P ≤ 0.05) values for pH24, colour coordinates (L*, a*, b*, H° and C°) and the higher (P ≤ 0.05) carcass temperature and shear force values relative to the other treatments. Pork from pigs fed the homemade grain-based diets had higher (P ≤ 0.05) contents of total FA, total PUFA, individual and total n-6 PUFA than pork from pigs fed the other diets. Pig carcasses stunned with a gun had higher (P ≤ 0.05) pH45, pH24 and shear force values than those not stunned. The homemade grain-based diet improved carcass attributes and fatty acid profiles of pigs raised and slaughtered on SUFs, stunning enhanced pork physical quality attributes while the kitchen-bakery-vegetable waste-based diet, cervical spine sticking treatment produced less desirable pork physical attributes.
Anti-phenolic glycolipid antibodies in Mycobacterium bovis infected cattle
(Elsevier, 2025-06) Zhou, Zijie; Van Hooij, Anouk; Van Dijk, J. Hessel M.; Musch, Nina; Pierneef, Louise; Khalid, Hamza; Franken, Kees; Holder, Thomas; Watt, Neil; Michel, Anita Luise; Codee, Jeroen D.C.; Vordermeier, Martin; Corstjens, Paul L.A.M.; Van der Heijden, Elisabeth M.D.L.; Hope, Jayne C.; Geluk, Annemieke
Mycobacterium bovis, the causative agent of bovine tuberculosis (bTB), causes significant financial losses in the agricultural industry. Additionally, M. bovis transmission from animals to humans can result in zoonotic TB, especially in low- and middle-income countries (LMICs), highlighting the need to enhance One Health surveillance to mitigate this threat. Antibodies directed against a major mycobacterial cell wall component of M. leprae, phenolic glycolipid-I (PGL-I), have shown excellent performance in identifying M. leprae infection in humans and animals. In this study, we therefore investigated whether antibodies against M. bovis PGL similarly represent a useful biomarker for M. bovis infection in cattle. Comparing sera from naturally M. bovis-infected and the single intradermal comparative cervical tuberculin test (SICCT)-negative cattle, we assessed the potential of M. bovis PGL antibodies to identify this mycobacterial infection. Our results show that serum levels of anti-M. bovis PGL IgG and -IgM in M. bovis-infected cattle were significantly higher than in the SICCT-negative cattle. The sensitivity for anti-M. bovis PGL IgM in infected animals was, however, moderate (44.9 %) and the false-positive rate was 6.3 % in SICCT-negative cattle. Notably, vaccination with BCG- or heat-killed M. bovis did not affect serum levels of anti-M. bovis PGL IgM in cattle. Moreover, none of the 57 anti-M. bovis PGL-seropositive cattle tested positive in the anti-M. leprae PGL-I assay. This study shows for the first time that anti M. bovis PGL antibodies can be detected in infected cattle: anti-M. bovis PGL IgM is a highly specific, but moderately sensitive biomarker for M. bovis infection in cattle, showing potential for differentiate infected from vaccinated animals (DIVA). It could be a valuable component in a multi-biomarker approach for diagnosing bTB.
Are there benefits of culture-based detection of over histopathology?
(AOSIS, 2025-02) Hlokwe, Motlatso T.; Masina, Nomawethu Shelly; Letsoko, Boitumelo; Davey, Sewellyn C.; Michel, Anita Luise
Paratuberculosis (Johne’s disease) has devastating outcomes on ruminant health and impacts on national and international trade. The current work assessed the diagnostic value of the VersaTREK automated liquid culture system in isolating Mycobacterium avium subspecies paratuberculosis (MAP) from faecal and intestinal tissue samples from ovine under South African conditions and compared it with the current method of choice, histopathological examination. Intestinal tissue and faecal samples from 111 sheep (including complete set from 104 slaughter sheep from flocks with a history of MAP infection as well as incomplete sample sets from 7 sheep) were analysed using the liquid culture method. One set of tissues was subjected to histopathological examination. Deoxyribonucleic acid (DNA) extracted from culture isolates was subjected to polymerase chain reaction (PCR) amplification using primers that target the IS900 regions of the MAP for species verification. Overall, the VersaTREK automated liquid culture in combination with IS900 PCR showed a comparable level of detection in tissues (12.6%) as histopathology (13.5%), but the detection rate for faecal samples was lower than for tissues (10.8%). A combination of histopathology and faecal culture increased the detection rate from 13.5% (n = 14/104) and 9.6% (n = 10/104), respectively, to 15.4% (n = 16/104). CONTRIBUTION : Our findings highlight the diagnostic utility of the VersaTREK automated liquid culture system in detecting MAP in ovine samples collected both ante and postmortem. However, an inhibitory effect on the MAP isolation rate observed when the antibiotic cocktail was added to the culture medium warrants further investigation. The outcome of the study is beneficial in guiding the strategic planning of the nationwide control programme.
Inequities underlie the alarming resurgence of Tuberculosis as the world's top cause of death from an infectious disease - breaking the silence and addressing the underlying root causes
(Elsevier, 2025-03) Zumla, Alimuddin; Sahu, Suvanand; Ditiu, Lucica; Singh, Urvasha; Park, Young-Joon; Yeboah-Manu, Dorothy; Osei-Wusu, Stephen; Asogun, Danny; Nyasulu, Peter; Tembo, Africa John; Kapata, Nathan; Tembo, John; Alyaqoubi, Fatma; Al Maani, Amal; Blumberg, Lucille Hellen; Zumla, Adam; Ahmed, Rizwan; Go, Unyeong; Hui, David; Goletti, Delia; Petersen, Eskild
No abstract available.
Prevalence of methicillin-resistant Staphylococcus aureus in livestock production system of Nigeria : a systematic review
(Istanbul University, 2025-01) Gaddafi, Mohammed Sani; Yakubu, Yusuf; Bello, Muhammad Bashir; Lawal, Habiba; Bitrus, Asinamai Athliamai; Musawa, Ibrahim Aliyu; Fasina, Folorunso Oludayo
Recently, methicillin-resistant Staphylococcus aureus (MRSA) has been identified as a growing concern in livestock. Animals can serve as reservoirs for MRSA, and the bacteria can be transmitted to humans who are in close contact with animals colonized by MRSA. This study evaluated the prevalence, potential source, and vehicle in the emergence and transmission of livestock-associated MRSA in Nigeria’s livestock production systems over the past decade. A systematic search was conducted on Web of Science, PubMed, Google Scholar, and Scopus databases to identify relevant studies published between 2012 and 2022. Standardized keywords were used. 28 eligible articles were included in the review, and our systematic review protocol was published in Prospero (Registration number: CRD42023431777). The occurrence of MRSA varied across the studies analyzed, ranging from 0% to 53.9%. Specifically, in poultry, the prevalence ranged from 7.9% to 37.5%; in cattle, from 3.21% to 29%; in pigs, from 0% to 53.9%; and in sheep and goats, from 4.4% to 25%. Among livestock farm/abattoir workers, the prevalence of MRSA ranged from 3.1% to 71.4%. The MRSA isolates from Nigeria’s livestock production systems displayed pathogenic potential with various S. aureus protein A (spa) types and clonal complexes (CC) as determined by Based Upon Repeat Pattern (BURP) analysis. These isolates carried genes associated with virulence factors such as enterotoxins, exfoliative toxins, and Panton-Valentine Leukocidin (PVL). One reviewed study documented the identification of the characteristic livestock-associated MRSA CC398 using Multilocus Sequence Typing (MLST) analysis. The livestock production system serves as a potential source and vehicle for the emergence and transmission of MRSA in Nigeria. To effectively prevent and control these infections, continuous monitoring using the “One Health” approach is recommended.
Molecular characterization of virulence and resistance genes in Salmonella strains isolated from chickens sold at the informal chicken market in Gauteng Province, South Africa
(Wiley, 2024-04) Mokgophi, Thelma M.; Gcebe, Nomakorinte; Fasina, Folorunso Oludayo; Adesiyun, Abiodun Adewale
This cross-sectional study determined the occurrence of virulence and antimicrobial resistance genes in Salmonella strains recovered from chicken obtained from informal markets in Gauteng province, South Africa. The study also assessed the relationship between these characteristics, the source, the type of samples, and the serotypes of Salmonella isolates. A total of 151 samples (cloacal swabs, chicken carcasses, and carcass drips) were randomly collected from 47 informal market outlets in six townships in Gauteng province. Salmonella spp. was isolated and identified based on ISO 6579:2002 methods and confirmed by polymerase chain reaction (PCR) targeting invA gene fragment. Conventional PCR was used to detect 12 virulence and 18 antimicrobial resistance (AMR) genes in Salmonella spp. The most frequently detected virulence genes were invA (100%), shdA (91%), mgtB (87.7%), and sopE (81%), but considerably low for spvC (2.2%), sefC (1.5%), and pefC (0.4%). The differences in detection frequency were statistically significant (p < 0.05). Tetracycline-resistant genes tetA (34.7%) and tetB (16%) were the most frequently detected, while Betalactam- resistant genes blaTEM (0.4%), blaCMY-2 (0.4%) and quinolones resistant gene qnrS (0.4%) were detected in low frequency (p < 0.05). The locations of the outlets and the types of samples were significantly associated with detecting some virulence and AMR genes. Significant but moderately to substantial positive correlations were observed for qnrS, sul2; shdA, and mgtB genes. The pipA and spiC were, however, substantially negatively correlated. Our findings show that detecting these virulence and AMR genes in Salmonella isolates serves as a potential health hazard to the public, environment, and poultry farming in Gauteng, South Africa.
Cutting-edge technology for diagnosing cattle abortions
(Plaas Publishing, 2025-03) Marais, Susan; melvyn.quan@up.ac.za
Researchers at the University of Pretoria (UP) are optimistic about their breakthrough to help solve one of the livestock sector’s most pressing issues, namely abortions in heifers and cows. The study in question was funded by Red Meat Research and Development South Africa (RMRD SA).
Unravelling the maternal evolutionary history of the African leopard (Panthera pardus pardus)
(PeerJ Inc., 2024-04) Morris, Declan R.; McWhorter, Todd J.; Boardman, Wayne S.J.; Simpson, Gregory J.G.; Wentzel, Jeanette Maria; Coetzee, Jannie; Moodley, Yoshan
The African leopard (Panthera pardus pardus) has lost a significant proportion of its historical range, notably in north-western Africa and South Africa. Recent studies have explored the genetic diversity and population structure of African leopards across the continent. A notable genetic observation is the presence of two divergent mitochondrial lineages, PAR-I and PAR-II. Both lineages appeared to be distributed widely, with PAR-II frequently found in southern Africa. Until now, no study has attempted to date the emergence of either lineage, assess haplotype distribution, or explore their evolutionary histories in any detail. To investigate these underappreciated questions, we compiled the largest and most geographically representative leopard data set of the mitochondrial NADH-5 gene to date. We combined samples (n = 33) collected in an altitudinal transect across the Mpumalanga province of South Africa, where two populations of leopard are known to be in genetic contact, with previously published sequences of African leopard (n = 211). We estimate that the maternal PAR-I and PAR-II lineages diverged approximately 0.7051 (0.4477–0.9632) million years ago (Ma). Through spatial and demographic analyses, we show that while PAR-I underwent a mid-Pleistocene population expansion resulting in several closely related haplotypes with little geographic structure across much of its range, PAR-II remained at constant size and may even have declined slightly in the last 0.1 Ma. The higher genetic drift experienced within PAR-II drove a greater degree of structure with little haplotype sharing and unique haplotypes in central Africa, the Cape, KwaZulu-Natal and the South African Highveld. The phylogeographic structure of PAR-II, with its increasing frequency southward and its exclusive occurrence in south-eastern South Africa, suggests that this lineage may have been isolated in South Africa during the mid-Pleistocene. This hypothesis is supported by historical changes in paleoclimate that promoted intense aridification around the Limpopo Basin between 1.0–0.6 Ma, potentially reducing gene flow and promoting genetic drift. Interestingly, we ascertained that the two nuclear DNA populations identified by a previous study as East and West Mpumalanga correspond to PAR-I and PAR-II, respectively, and that they have come into secondary contact in the Lowveld region of South Africa. Our results suggest a subdivision of African leopard mtDNA into two clades, with one occurring almost exclusively in South Africa, and we identify the potential environmental drivers of this observed structure. We caution that our results are based on a single mtDNA locus, but it nevertheless provides a hypothesis that can be further tested with a dense sample of nuclear DNA data, preferably whole genomes. If our interpretation holds true, it would provide the first genetic explanation for the smaller observed size of leopards at the southernmost end of their range in Africa.
A rapid tick exposure test for monitoring acaricide resistance in Rhipicephalus sanguineus sensu lato ticks on dogs
(BMC, 2024-09) Jongejan, Frans; Berger, Laura; Papadopoulos, Elias; Reck, Jose; Ferreira, Priscila T.; Scott, Fabio B.; De Avelar, Barbara R.; Guimarães, Brena G.; Correia, Thais R.; Hulsebos, Iris; Petersen, Alita; Klafkeg, Guilherme; Frans.Jongejan@up.ac.za
BACKGROUND: Brown dog ticks (Rhipicephalus sanguineus sensu lato) are vectors of pathogens adversely affecting the health of dogs in many regions of the world. The three-host life cycle of R. sanguineus s.l., with all stages feeding on dogs, can lead to an uncontrolled build-up of large tick populations if not controlled by acaricides. However, frequent tick control on dogs using acaricides has led to the emergence of resistance to permethrin and fipronil. Currently, the larval packet test (LPT) is the standard tick resistance test, which is laborious, requires laboratory facilities, and takes at least 6 weeks before larvae derived from engorged female ticks can be tested. Our novel approach is to expose semi-engorged adult ticks to acaricides immediately after removing them from dogs, obtaining results within 24 h. METHODS Adult ticks from three laboratory colonies of R. sanguineus s.l. were tested in RaTexT®, a rapid tick exposure test in which ticks were confined to small compartments and exposed to an acaricide-impregnated, specially designed matrix. Resistance was confirmed by testing larvae derived from the same laboratory colonies using the LPT. RaTexT® was also used to determine the susceptibility of R. sanguineus acaricides in dog shelters. RESULTS RaTexT® detected resistance to permethrin in adult R. sanguineus s.l. ticks from two Brazilian laboratory colonies compared to a susceptible laboratory strain originating in Greece. Resistance was confirmed by LPT testing of larvae from the same colonies with resistance factors between 2.2 and 3.1. All laboratory strains were susceptible to fipronil. A suspected case of fipronil resistance at a dog shelter in Caxias do Sul, Brazil, was resolved within 24 h by testing adult ticks in RaTexT® and could be attributed to improper treatment. CONCLUSIONS: RaTexT® is a valuable tool for monitoring the development of resistance to synthetic pyrethroids or phenylpyrazoles in tick-infested dogs.
Resistance intensity test (RIT) : a novel bioassay for quantifying the level of acaricide resistance in Rhipicephalus microplus ticks
(BMC, 2024-11) Jongejan, Frans; Berger, Laura; Homminga, Laura; Hulsebos, Iris; Petersen, Alita; Ferreira, Priscila T.; Reck, Jose; Klafkeg, Guilherme; Frans.Jongejan@up.ac.za
BACKGROUND: One bioassay for detecting acaricide resistance in livestock ticks is the adult immersion test (AIT), wherein engorged ticks are briefly immersed into a solution of a particular acaricidal compound and examined for mortality, their egg-laying capacity and offspring hatchability in vitro. Usually, the recommended label dose or an established discriminating dose of an acaricide is used to determine high mortality (≥95%) of susceptible tick strains. Such a test intends to detect the presence of resistance in a tick population. However, the adult immersion test does not directly translate the bioassay results to the predicted efficacy in the field. In this paper, we used the AIT as an initial screening bioassay supplemented with the resistance intensity test (RIT), a novel larval-based bioassay, wherein the resistance level can be determined and translated to the expected field efficacy. This was done by adopting World Health Organisation (WHO) guidelines for resistance detection in mosquitoes, which combines a 1×recommended dose with 5×and 10×concentrated doses to reveal low, moderate and high resistance intensity, respectively. METHODS: Engorged Rhipicephalus microplus ticks were collected from cattle at six different ranches across Rio Grande do Sul, Brazil, as part of the state’s acaricide resistance surveillance program. Groups of adult ticks from each field collection were subjected to the AIT from each field sample. Additionally, engorged female ticks from each ranch were allowed to lay eggs, and their larval progeny aged 14 to 28 days were then used in the RIT. Deltamethrin and a combination of cypermethrin, chlorpyrifos and piperonyl butoxide were used in both tests, and the results were statistically analysed. RESULTS: The in vitro efficacy of deltamethrin against adult ticks in the AIT ranged between 8.74% and 25.38%. The corresponding RIT results on their larval progeny indicated a high resistance level. In the immersion test, the in vitro efficacy of the combination of cypermethrin, chlorpyrifos, and piperonyl butoxide against adult ticks ranged between 49.31% and 100%. The corresponding RIT results on their larval progeny indicated a similar response ranging from fully susceptible to low or moderate resistance. The Pearson correlation coefficient (r=0.883) showed a high correlation between tick mortality at the 1×recommended concentrations of acaricides in both tests. CONCLUSIONS: The resistance intensity test is a valuable addition to the range of bioassays currently available for detecting acaricide resistance by determining the level of acaricide resistance. This is relevant to whether or not to continue using a particular acaricidal class for controlling cattle ticks.
Intra- and interspecific variation of Amblyomma ticks from southern Africa
(BMC, 2024-08) Smit, Andeliza; Mulandane, Fernando; Labuschagne, Martinet; Wójick, Stephané H.; Malabwa, Choolwe; Sili, Gourgelia; Mandara, Stephen; Dlamkile, Zinathi; Ackermann, Rebecca; Vineer, Hannah Rose; Stoltsz, Wilhelm Heinrich; Huber, Karine; Horak, Ivan Gerard; Morar‑Leather, Darshana; Makepeace, Benjamin L.; Das Neves, Luis Carlos Bernardo G.; u14023190@tuks.co.za
BACKGROUND: Amblyomma spp. ticks, known for their long mouthparts, bright ornate appearance and aggressive hunting behaviour, are vectors of a number of important pathogens. In southern Africa, 17 Amblyomma spp. are currently documented. Of these species, Amblyomma hebraeum and Amblyomma variegatum have been well studied due to their wide geographical range and their status as competent vectors of pathogens that are of veterinary and medical importance. Studies on other Amblyomma spp. in southern Africa have been neglected, fostering ongoing debates on the validity of certain species such as Amblyomma pomposum. This study investigated the inter- and intra-species variation of Amblyomma ticks collected in southern Africa, focusing on resolving the dispute about A. pomposum and A. variegatum being distinct species. METHODS: Four Amblyomma tick species were collected from Angola, Mozambique, South Africa, Zambia and Zimbabwe, and were identified morphologically as Amblyomma eburneum (208), A. hebraeum (4758), A. pomposum (191) and A. variegatum (2577) using identification keys. Gene amplification targeting the 12S and 16S rRNA, cytochrome oxidase I, cytochrome B and internal transcribed spacer-2 genes was conducted for 204 ticks, for which varying success was achieved during amplification for each of the markers. Maximum likelihood analyses were performed in IQ-TREE. RESULTS: The phylogenetic topologies and ABGD analyses of each individual gene clustered A. pomposum within the A. variegatum clade, while clearly separating A. eburneum and A. hebraeum from all other species. None of the genetic markers indicated intraspecific structuring on the basis of geographical origin, despite great distances between sampling sites. CONCLUSION: Our study concludes that there is insufficient molecular evidence to differentiate A. pomposum and A. variegatum from each other. We highlight the need for whole mitochondrial genome sequencing of these two species to resolve the ongoing controversies. Furthermore, we propose mating and hybrid viability studies between the two species to confirm their reproductive isolation.
RaTexT® : a novel rapid tick exposure test for detecting acaricide resistance in Rhipicephalus microplus ticks in Brazil
(BMC, 2024-08) Jongejan, Frans; Berger, Laura; Reck, Jose; Ferreira, Priscila T.; De Jesus, Mariana S.; Scott, Fabio B.; De Avelar, Barbara R.; Guimarães, Brena G.; Correia, Thais R.; Muhanguzi, Dennis; Vudriko, Patrick; Byaruhanga, Joseph; Tumwebaze, Maria; Nagagi, Yakob; Temba, Violet; Biguezoton, Abel S.; Farougou, Souaibou; Adehan, Safiou Bienvenu; Jumba, Humphrey; Homminga, Laura; Hulsebos, Iris; Petersen, Alita; Klafkeg, Guilherme; Frans.Jongejan@up.ac.za
BACKGROUND: Acaricide resistance in cattle ticks is a significant concern in (sub)tropical regions, particularly Brazil. The Larval Packet Test (LPT) is the standard laboratory bioassay for resistance diagnosis, which requires triplicates of seven acaricidal dilutions plus controls to cover larval mortalities ranging between 0 and 100%. The value of the LPT lies in providing resistance ratios based on the ratio between the LC50 calculated with potentially resistant and susceptible ticks. However, LC50 ratios are difficult to translate into practical advice for farmers. Moreover, LPT requires laboratory facilities to maintain susceptible tick colonies, and it takes 6 weeks to obtain the larvae to be tested by LPT derived from engorged female ticks collected from cattle in the field. Our novel approach was twofold: first, we upgraded the LPT to the Resistance Intensity Test (RIT) by adopting the latest WHO guidelines for resistance detection in mosquitoes, which combines a 1 × recommended dose with 5 × and 10 × concentrated doses to reveal low, moderate and high resistance intensity, respectively. This reduced the number of test papers and tick larvae and, more importantly, provided relevant information on the resistance level. Our second innovative step was to abolish testing larvae entirely and expose partly engorged adult ticks to the same acaricidal doses immediately after removing them from cattle in the field. This resulted in the Rapid Tick exposure Test (RaTexT®), wherein partly engorged adult ticks were exposed to an acaricide-impregnated, specially designed matrix providing test results within 24 h. This approach directly compared resistance detection in tick larvae in the RIT with resistance in adult ticks in RaTexT®. METHODS: Laboratory validation was conducted in Brazil with resistant and susceptible colonies of Rhipicephalus microplus ticks. For field validation, adult R. microplus ticks collected from different cattle farms in Brazil were evaluated for resistance to RaTexT®, and the results regarding their larval progenies were compared with those for the RIT. Partly engorged adult ticks derived from cattle infested with laboratory and field strains of R. microplus were exposed to deltamethrin in RaTexT® containers, which contained six rows of four interconnected compartments, accommodating five to eight semi-engorged female ticks with a preferred size ranging between 5 and 8 mm. The corresponding larvae of each strain were exposed in the RIT to the same deltamethrin concentrations in filter papers. RESULTS: In RaTexT®, mortality in adult ticks from a resistant strain of R. microplus from Seropédica in Brazil was 38.4%, 54.2% and 75.0% at the 1 ×, 5 × and 10 × doses of deltamethrin, respectively. In RIT, mortality of larvae from the same resistant strain was 2.0%, 4.9% and 19.5% at 1 ×, 5 × and 10 × doses, respectively. The results of RaTexT® and RIT agreed since both tests identified a high level of resistance based on a cut-off of 90% mortality. In RaTexT®, mortality of adult ticks from a susceptible strain originating from Porto Alegre was 73.8%, 92.9% and 97.6% at the 1 ×, 5 × and 10 × doses, respectively. In RIT, mortality of larvae from the susceptible strain was 95.2%, 95.2% and 96.8% at the 1 ×, 5 × and 10 × doses, respectively. Interestingly, both tests identified a low number of unexpected resistant individuals in the susceptible strain since the mortality of neither larvae nor adults reached 100%. This effect remained unnoticed in the LPT, wherein a resistance ratio of 159.5 was found based on the LC50 of the resistant strain divided by the LC50 of the susceptible strain. Next, RaTexT® was compared with RIT using adult and larval ticks derived from three field strains of R. microplus in Brazil. RaTexT® detected high levels of resistance to deltamethrin in adult ticks in all strains, which was confirmed in larvae tested by the RIT. Both tests agreed on the same resistance level with significantly lower mortality rates in larvae than in adult ticks. CONCLUSIONS: RaTexT® is a novel rapid pen-site test for detecting acaricide resistance in adult livestock ticks. It potentially replaces laborious tests using larval ticks and provides results within 24 h relevant to acaricide resistance management of livestock ticks.
African swine fever diagnosis in Africa : challenges and opportunities
(MDPI, 2024-04) Penrith, Mary-Louise; Van Emmenes, Juanita; Hakizimana, Jean N.; Heath, Livio; Kabuuka, T.; Misinzo, Gerald; Odoom, Theophilus; Wade, Abel; Zerbo, Habibata L.; Luka, Pam D.
The global spread of African swine fever (ASF) in recent decades has led to the need for technological advances in sampling and diagnostic techniques. The impetus for these has been the need to enable sampling by lay persons and to obtain at least a preliminary diagnosis in the field for early control measures to be put in place before final laboratory confirmation. In rural Africa, rapid diagnosis is hampered by challenges that include lack of infrastructure as well as human and financial resources. Lack of animal health personnel, access to affordable means to transport field samples to a laboratory, and lack of laboratories with the capacity to make the diagnosis result in severe under-reporting of ASF, especially in endemic areas. This review summarizes the challenges identified in gap analyses relevant to low- and middle-income countries, with a focus on Africa, and explore the opportunities provided by recent research to improve field diagnosis and quality of diagnostic samples used. Sampling techniques include invasive sampling techniques requiring trained personnel and non-invasive sampling requiring minimal training, sampling of decomposed carcass material, and preservation of samples in situations where cold chain maintenance cannot be guaranteed. Availability and efficacy of point-of-care (POC) tests for ASF has improved considerably in recent years and their application, as well as advantages and limitations, are discussed. The adequacy of existing laboratory diagnostic capacity is evaluated and opportunities for networking amongst reference and other laboratories offering diagnostic services are discussed. Maintaining laboratory diagnostic efficiency in the absence of samples during periods of quiescence is another issue that requires attention, and the role of improved laboratory networking is emphasized. Early diagnosis of ASF is key to managing the disease spread. Therefore, the establishment of the Africa Chapter of the Global African Swine Fever Research Alliance (GARA) increases opportunities for collaboration and networking among the veterinary diagnostic laboratories in the region.
Genome sequencing of historical encephalomyocarditis viruses from South Africa links the historical 1993/4 savanna elephant (Loxodonta africana) outbreak to cryptic mastomys rodents
(MDPI, 2024-03) Van Meer, Vanessa; Paweska, Janusz Tadeusz; Swanepoel, Robert; Grobbelaar, Antoinette; Bastos, Armanda D.S.; armanda.bastos@up.ac.za
From 1993 to 1994, 64 free-ranging elephants (Loxodonta africana) succumbed to encephalomyocarditis in the Kruger National Park, South Africa, of which 83% were adult bulls. Mastomys rodents were implicated as the reservoir host of the Encephalomyocarditis virus (EMCV) based on serology and RT-PCR. However, in the absence of sequence-confirmation of both the virus and the rodent host, definitive links between the elephant outbreak strains and rodent reservoir could not be established. In this study, we generate the first reference genome sequences for three historical EMCVs isolated from two Mastomys rodents and one Mastomys-associated mite, Laelaps muricola, in Gauteng Province, South Africa, in 1961. In addition, near-complete genome sequences were generated for two elephant outbreak virus strains, for which data were previously limited to the P1 and 3D genome regions. The consensus sequence of each virus was determined using a PCRSanger sequencing approach. Phylogenetic analysis confirmed the three near-identical (99.95–99.97%) Mastomys-associated viruses to be sister to the two near-identical (99.85%) elephant outbreak strains, differing from each other at 6.4% of sites across the ~7400-nucleotide region characterised. This study demonstrates a link between Mastomys-associated viruses and the historical elephant outbreak strains and implicates Mastomys as reservoirs of EMCV in South Africa.
Molecular characterisation and antibody response to bovine respiratory syncytial virus in vaccinated and infected cattle in Turkey
(MDPI, 2024-04) Aydin, Ozge; Yilmaz, Aysun; Turan, Nuri; Richt, Juergen A.; Yilmaz, Huseyin
Bovine respiratory syncytial virus (BRSV) is one of the most important respiratory pathogens of cattle. In this study, frequency of infection, analysis of variants, and the immune status of vaccinated and non-vaccinated cattle were studied. Blood (n = 162) and nasal/oropharyngeal (n = 277) swabs were collected from 62 cattle herds in Turkey. Lung samples (n = 37) were also taken from dead animals and abattoirs. Antibodies to BRSV were detected in 76 (46%) out of 162 sera. The antibody levels in the vaccinated and non-vaccinated groups were statistically significant. Among 277 nasal/oropharyngeal swabs and 37 lungs, ten nasal/oropharyngeal and four lung samples were positive for BRSV-RNA. BRSV-G gene sequences of 5 out of 14 RT-PCR positive samples showed that all viruses clustered as Group-III in phylogenetic analysis with 88–100% homology. Similarity with previous Turkish BRSVs was 89–98%, and that with BRSVs detected in the USA and Czechia was 89.47–93.12%. BRSV continues to circulate in Turkish cattle, and vaccination seems beneficial in preventing BRSV. The diversity of the BRSVs found in this study needs be considered in vaccination strategies.
Evidence for horizontal transmission and recirculation of Shiga toxin-producing Escherichia coli in the beef production chain in South Africa using whole genome sequencing
(MDPI, 2024-09) Onyeka, L.O. (Libby); Adesiyun, Abiodun Adewale; Ismail, Arshad; Allam, Mushal; Keddy, Karen H.; Thompson, P.N. (Peter N.); peter.thompson@up.ac.za
Please read abstract in article.
Brucellosis seropositivity using three serological tests and associated risk factors in abattoir workers in Gauteng province, South Africa
(MDPI, 2024-01) Kolo, Francis Babaman; Adesiyun, Abiodun Adewale; Fasina, Folorunso Oludayo; Harris, Bernice Nerine; Rossouw, Jennifer; Byaruhanga, Charles; De Wet Geyer, Hermanus; Blumberg, Lucille Hellen; Frean, John; Van Heerden, Henriette
Abattoir workers are liable to zoonotic infections from animals and animal products, primarily to diseases with asymptomatic and chronic clinical manifestations in animals, such as brucellosis. No published reports exist on the seroprevalence of brucellosis in abattoir workers in South Africa. Therefore, this cross-sectional study was conducted to estimate the occurrence and risk factors for Brucella exposure in abattoir workers in Gauteng Province. A total of 103 abattoir workers and managers from 6 abattoirs, where brucellosis-positive slaughtered cattle and sheep were previously detected, were interviewed and tested with serological assays using the Rose Bengal test (RBT), BrucellaCapt, and IgG-ELISA. A pre-tested questionnaire was administered to consenting respondents to obtain information on risk factors for brucellosis. Of the 103 respondents tested, the distribution of female and male workers was 16 (15.5%) and 87 (84.5%), respectively. The seroprevalence for exposure to brucellosis was 21/103 (20.4%, 95%CI: 13.1–29.5) using a combination of RBT, BrucellaCapt, or IgG-ELISA. For test-specific results, seroprevalences by RBT, BrucellaCapt, and IgG-ELISA were 13/103 (12.6%, 95%CI: 6.9–20.6), 9/103 (8.74%, 95%CI: 4.1–15.9), and 18/103 (17.5%, 95%CI: 10.7–26.2), respectively. Low-throughput abattoirs were identified as associated risks, as 29.3% of workers were seropositive compared with 12.7% of workers in high-throughput abattoirs, which highlights that direct contact at abattoirs poses higher risk to workers than indirect and direct contact outside abattoirs. This study confirms the occurrence of Brucella spp. antibodies among abattoir workers in South Africa, possibly due to occupational exposure to Brucella spp., and highlights the occupational hazard to workers. Furthermore, findings underscore that abattoir facilities can serve as points for active and passive surveillance for indicators of diseases of public health importance. We recommend periodic implementation of brucellosis testing of abattoir workers country-wide to establish baseline data for informing appropriate preventive practices and reducing the potential burden of infection rates among these high-risk workers.
Temporal and serotypic dynamics of Actinobacillus pleuropneumoniae in South African porcine populations : a retrospective study from 1985 to 2023
(MDPI, 2024-07) Seakamela, Emmanuel M.; Henton, Marijke M.; Jonker, Annelize; Kayoka-Kabongo, Prudence Ngalula; Matle, Itumeleng
Actinobacillus pleuropneumoniae is a major bacterial pathogen causing porcine pleuropneumoniae, which is a disease of notable economic impact and high fatality rates among pigs worldwide. It has been reported that 19 distinct serotypes of this bacterium exist. Despite its global prominence, there exists a scarcity of information regarding its prevalence and distribution in South Africa. Thus, this study used laboratory records to investigate the serotype diversity, temporal distribution, and seasonal patterns of A. pleuropneumoniae isolated from porcine samples spanning from 1985 to 2023 within South Africa. Data from laboratory registries of 354 cases, obtained from three veterinary laboratories in South Africa, were analyzed. The data were categorized into two-time frames: term 1, covering 1985 to 2001, and term 2, spanning from 2002 to 2023. The dataset identified 11 different serotypes, with serotype 7 being the most prevalent at 22.7% (n = 62), which was followed by serotype 5 at 13.8% (n = 42). The study highlighted variations in the prevalence of serotypes among diseased animals over a 38-year period. Serotypes 3, 5, 7 and 8 were commonly observed during this time, while serotype 4 was absent from 1985 to 2001, and serotypes 1, 6, and 10 were absent from 2002 to 2023. The distribution of serotypes showed a diverse variation in the age of affected animals, clinical manifestation, and seasonal occurrence. Key findings revealed that serotype 7 was the most prevalent across all seasons with the highest occurrence in winter. Additionally, Gauteng province showed the highest prevalence of various serotypes. The information collected during this study will serve as a baseline for future epidemiological studies as well as inform control strategies.

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