Introduction
Bovine cysticercosis negatively impacts vulnerable communities and the beef industry, and it poses a public health burden. The economic losses are attributed to carcass condemnations, treatment of lightly infected carcasses, their subsequent drop in value post-treatment, and, indirectly, restriction on exports (Jansen et al. Reference Jansen, Dorny, Berkvens and Gabriël2018). The adult parasite is the cause of Taenia saginata taeniosis, a cosmopolitan neglected cyclozoonoses estimated to affect 50 million people worldwide (OIE 2005; WHO 2016). The adult helminth resides in the small intestines of man, and the metacestode stage parasitizes the muscles of cattle and occasionally other bovids (Grove Reference Grove1990). Tapeworm carriers rarely report clinical symptoms; however, they may present with nausea, abdominal discomfort, emesis, diarrhoea, weight loss, peri-anal symptoms, and, rarely, cholecystitis (Hakeem et al. Reference Hakeem, Rashid, Khuroo and Bali2012; Uyguer-Bayramicli et al. Reference Uygur-Bayramiçli, Ak, Dabak, Demirhan and Ozer2012).
Bovine cysticercosis is asymptomatic. Post-mortem examination (meat inspection) of slaughtered carcasses through incision, palpation, and visual inspection remains the main method for screening infected carcasses. It is, however, insensitive due to its reliance on predilection sites and the intensity of infestation (Minozzo et al. Reference Minozzo, Gusso, de Castro, Lago and Soccol2002; Wanzala et al. Reference Wanzala, Onyango-Abuje, Kang’ethe, Zessin, Kyule, Baumann, Ochanda and Harrison2003; Lopes et al. Reference Lopes, Santos, Soares, Nunes, Mendonça, de Lima, Sakamoto, Costa, Thomaz-Soccol, Oliveira and Costa2011; Jansen et al. Reference Jansen, Dorny, Berkvens, Van Hul, Van den Broeck, Makay, Praet, Eichenberger, Deplazes and Gabriël2017; Jansen et al. Reference Jansen, Dorny, Berkvens and Gabriël2018). Sources of false positives may stem from morphologically similar pathological lesions such as small abscesses, neoplasms, fat tissue, and other tissue parasites (Ogunremi et al. Reference Ogunremi, MacDonald, Geerts and Brandt2004; Abuseir et al. Reference Abuseir, Epe, Schnieder, Klein and Kühne2006). Serological tests for T. saginata detection in cattle have been reported to have inconsistent sensitivities, have rather poor performances in detecting light infections, and cross-react with other taeniid infections (Onyango-Abuje et al. Reference Onyango-Abuje, Hughes, Opicha, Nginyi, Rugutt, Wright and Harrison1996a; Wanzala et al. Reference Wanzala, Onyango-Abuje, Kang’ethe, Ochanda and Harrison2002; Jansen et al. Reference Jansen, Dorny, Berkvens, Van Hul, Van den Broeck, Makay, Praet, Eichenberger, Deplazes and Gabriël2017). Still, serological tests offer a higher potential performance than meat inspection. Nevertheless, their limited commercial availability and restricted accessibility to researchers have led to a reliance on meat inspection in many studies. Additionally, serological tests are yet to be adapted for operational use in slaughterhouses.
The prevalence of bovine cysticercosis in Kenya has shown varying trends over time and across regions. Surveillance data are limited and have huge chronological gaps. Notably, however, Kenya is among the African countries referred to as having ‘hyperendemic pastoral cysticercosis’, characterized by a simultaneous high burden of T. saginata infection in humans and cattle (OIE 2005). Early reports from the 1960s revealed high prevalence rates, with 31.7% reported at Kenya Meat Commission (receives slaughter cattle countrywide) and an estimated 53% in the Narok region (Froyd Reference Froyd1960; Froyd Reference Froyd1965). Between 1974 and 1991, the prevalence ranged from 8% to 1.1% in different regions (Kangethe Reference Kang’ethe1995). In the late 1990s, the reported prevalence at Kenya Meat Commission was 7.6%. An aggregated prevalence estimate of 16% was observed in several pastoralist-occupied areas in the same duration, with the Narok region reporting the highest occurrence rate at 31% (Onyango-Abuje et al. Reference Onyango-Abuje, Nginyi, Rugutt, Wright, Lumumba, Hughes and Johnstone1996b). Findings from a study conducted in 2009 indicated the prevalence to be 3.2% in the Northern Turkana area (Asaava et al. Reference Asaava, Kitala, Gathura, Nanyingi, Muchemi and Schelling2009).
Another important meat parasite in cattle is Sarcocystis. The genus Sarcocystis represents over 200 heteroxenous cosmopolitan coccidian parasites of vertebrates. Only 26 have known life cycles, which commonly adopt a predator–prey pattern (Dubey Reference Dubey2015; Castro-Forero et al. Reference Castro-Forero, Bulla-Castañeda, López Buitrago, Díaz Anaya, Madeira de Carvalho and Pulido-Medellín2022). Carnivores and omnivores act as the definitive hosts and get infected upon ingesting infected muscles from intermediate hosts. In their gut, oocysts are excreted to contaminate the environment, leading to the acquisition of infection by intermediate hosts. The parasite adopts asexual forms in the intermediate host, leading to the formation of muscular sarcocysts. Pigs and cattle are the only recognized livestock intermediate hosts of zoonotic Sarcocystis spp. Cattle act as the intermediate host for seven known Sarcocystis spp. Two of these are zoonotic (i.e., S. hominis and S. heydorni). Intestinal sarcocystosis is, however, frequently asymptomatic, although nausea, inappetence, vomiting, diarrhoea, bloat, and stomachache have been reported (Fayer Reference Fayer2004; Dubey Reference Dubey2015; Castro-Forero et al. Reference Castro-Forero, Bulla-Castañeda, López Buitrago, Díaz Anaya, Madeira de Carvalho and Pulido-Medellín2022). Sarcocystis cruzi is the most significant Sarcocystis spp. in cattle, it is the most prevalent globally, and it is responsible for high economic losses. Canids act as the definitive host for S. cruzi. Infection with S. cruzi in cattle rarely manifests clinically; however, it is linked with the pathogenesis of bovine eosinophilic myositis (BEM). BEM leads to high economic losses as it necessitates carcass condemnation (Dubey Reference Dubey2015; Castro-Forero et al. Reference Castro-Forero, Bulla-Castañeda, López Buitrago, Díaz Anaya, Madeira de Carvalho and Pulido-Medellín2022; Dini et al. Reference Dini, Caffara, Jacinto, Benazzi, Gentile and Galuppi2023; Dubey and Rosenthal Reference Dubey and Rosenthal2023).
The status of Sarcocystis infection in cattle in Kenya is largely unknown. A clear and comprehensive epidemiological picture of T. saginata infections is also lacking in the country; data are limited and confounded by the use of poorly performing diagnostic tools. This study seeks to contribute to the growing body of knowledge in this area by estimating the occurrence of bovine cysticercosis in cattle from at-risk communities based on meat inspection, combined with molecular confirmation of the suspected T. saginata lesions. Moreover, lesions were also tested for Sarcocystis spp. as a potential differential diagnosis and to contribute to preliminary investigations into the occurrence of Sarcocystis spp. in Kenyan cattle.
Materials and methods
Study area
The study area was Narok County located in southwestern Kenya at coordinates 1015’S, 35037’E. It has a total area spanning 17,921.2 km2, which is fragmented into 6 sub-counties and 30 wards. The sub-counties are Kilgoris, Narok North, Narok South, Narok East, Narok West, and Emurua Dikirr (see Figure 1). The ambient temperature ranges between 12 and 28oC, and annual rainfall averages between 500 and 1800 mm. Economic activities include mining, crop farming, tourism, and livestock farming. Its cattle density is estimated at 1.5 million. Pastoralism production system is widely practiced. The human population is approximately 1,157,873 of which only 35% use improved sanitation and 20% use improved drinking water sources (KNBS 2019).
Figure 1. Map of Kenya depicting Narok County and its sub-counties.
Narok County has 5 main slaughterhouses and 14 active slaughter slabs with an average daily throughput of approximately 200 cattle carcasses (unpublished Narok County veterinary records). The animals that are slaughtered are primarily sourced locally. However, the Maasai community of pastoralists, who are the primary cattle keepers in the region, extend their presence to neighbouring Tanzania.
Sampling and sample size determination
A cross-sectional study design was employed. The sample size (n) for bovine carcasses was computed as per the proportions survey formulae by Thrusfield (Reference Thrusfield2005), where expected prevalence (Pexp) was set at 50% to maximize the sample size, the desired absolute precision (d) set at 0.05, and the confidence level set at 95%, to give a sample size of 384. However, additional sampling was conducted due to its positive effect on precision. Individual carcasses were selected by systematic random sampling. Sampling targeted 5/5 of the slaughterhouses and 5/14 of the slaughter slabs, with the selection of slaughter slabs being random.
Carcass inspection
The sampling was conducted from April to July 2021. Bovine carcasses were inspected for T. saginata cysticerci by a meat inspector accompanied by the researcher. This was done by examining the Triceps brachii muscles predilection site whereby three cuts of approximately 2-cm thickness were made using a sharp knife with subsequent visual identification of cysticerci if present (Meat Control Act 2012). Suspected tissue lesion sections of approximately 0.5 cm3 containing the cysticercus were excised and stored in labelled 2-ml vials containing 70% ethanol until analyses. The number of carcasses positive on visual inspection was noted. The number of cysticercus lesions detected, and their stage, was noted; they were classified as either viable or degenerated (Abuseir et al. Reference Abuseir, Epe, Schnieder, Klein and Kühne2006).
DNA extraction
One suspected cysticercus per carcass was utilized for DNA extraction. Where both viable and degenerated cysticerci were obtained from a single carcass, tissue from the viable cysticercus was used. DNA extraction was conducted as per the protocol from the manufacturer, DNeasy Blood & Tissue Kit (Qiagen, Hilden, Germany). Extracted DNA was stored at -20oC pending further tests.
Polymerase chain reaction-restricted fragment length polymorphism
A semi-nested polymerase chain reaction (PCR) technique was utilized to target the mitochondrial 12S rDNA gene of Taenia spp. The specific primers used in this PCR method and protocol were adapted from Geysen et al. (Reference Geysen, Kanobana, Victor, Rodriguez-Hidalgo, De Borchgrave, Brandt and Dorny2007). The forward primer was 5’-CTCAATAATAATCGAGGGTGACGG-3’, (ITM TnR, Primer 1), and the reverse primer was 5’-GTTTGCCACCTCGATGTTGACT-3’(TaenF, Primer 2) and 5’-CGTGAGCCAGGTCGGTTCTTAT-3’ (nTAE, Primer 3). The nested PCR (nPCR) was genus-specific, producing Taenia spp. amplicons of 789–798 bp with ITM TnR/nTAE primers. Extracted DNA was prepared in pairs of 1/1 dilution and 1/10 dilution for the first round of PCR (i.e., 5 μl DNA and 0.5 μl DNA templates). For the second round of PCR, a 0.5μl DNA template was used. The quantities of the constituents of the mastermix were 2 × Promega GoTaq Mastermix (Promega, Madison, USA) (12.5 μl both PCR rounds), nuclease-free water (6.7 μl round 1 PCR, and 11.2 μl round 2 PCR), Primer 1 (0.4 μl for both PCR rounds), Primer 2 and 3 (0.4 μl). Primers were constituted to a concentration of 25 pmol/ μl. A total volume of 25 μl PCR reaction mix was used for both rounds of PCR. Primers 1 and 2 were used for the first round of PCR, and Primers 1 and 3 for the second round of PCR. Amplification was conducted using Applied Biosystems Veriti Thermal Cycler®, with the following settings used for the 1st round PCR: initial denaturation at 95oC for 2 min, followed by 40 cycles of amplification of 92oC for 45 s, 57oC for 45 s, 72oC for 60 s, and a final elongation at 72oC for 10 min. The second round PCR utilized the same parameters, but the cycle number was reduced to 25. The amplicons were analyzed by electrophoresis in 2% (w/v) agarose gels for 60 min at 120 V, followed by ethidium bromide staining for 20–30 min and photography under UV illumination. Amplicons corresponding with Taenia spp. Positive wells from round 2 of PCR were further subjected to restriction endonuclease digestion using enzymes Ddel, Hinfl, and Hpal (New England Biolabs, Ipswich, USA). Post PCR, restricted fragment length polymorphism (RFLP) using the endonucleases achieves diagnostic DNA fragments, enabling the identification of Taenia species. Amplicons of 471 bp, 165 bp, and 128 bp are diagnostic for T. saginata. Where both the 1/1 dilution and 1/10 dilution samples gave positive amplification bands, the 1/10 nPCR product was preferred. The enzymes were used at their initial concentration of 10–20 U/μl and concentrated restriction enzyme buffers at 10×. The RFLP mastermix was constituted following the manufacturer’s instructions. The final mixture per sample comprised 6 μl of PCR products from round 2 of PCR and 9 μl of RFLP mastermix. The vials were then incubated at 37oC for 4 hrs. The digested products were analyzed by electrophoresis for 60 min at 120 V, on a 2% (w/v) agarose gel. A DNA size marker of 100 bp was included for reference. This was followed by ethidium bromide staining for 40 min and photography under UV illumination. Known positive controls for T. saginata were included in the RFLP analysis.
Echinococcus spp.-Taenia spp. multiplex polymerase chain reaction
All DNA isolates were subjected to an Echinococcus spp.-Taenia spp. multiplex PCR. This test targets sequences of part of the mitochondrial genes for NADH dehydrogenase subunit 1 (nad1) and the small subunit of ribosomal RNA (rrnS). The protocol utilized was adapted from Trachsel et al. (Reference Trachsel, Deplazes and Mathis2007). The assay is deemed more sensitive than the nPCR described by Geysen et al. (Reference Geysen, Kanobana, Victor, Rodriguez-Hidalgo, De Borchgrave, Brandt and Dorny2007) (pers. comm) and therefore a useful test for detecting Taenia spp, especially in populations where Taenia spp. is co-endemic with Echinococcus spp. A positive Taenia spp. amplicon is identified by a band weight of 267 bp. The oligonucleotide sequences for the primers used were as follows for E. multilocularis: 5’- TGCTGATTTGTTAAAGTTAGTGATC-3’(Primer-Cest1), 5’-CATAAATCAATGGAAACAACAACAAG-3’ (Cest2), E. granulosus, 5’-GTTTTTG TGTGTTACATTAATAAGGGTG-3’ (Cest4), 5’-GCGGTGTGTACMTGAGCTAAAC-3’ (Cest5) and Taenia spp. detection, 5’-YGAYTCTTTTTAGGGGAAGGTGTG-3’ (Cest3), and 5’-GCGGTGTGTACMTGAGCTAAAC-3’(Cest5). The amplification mixture volume per reaction was constituted to a total of 25 μl, and a DNA template of 0.5 μl was mixed with a cumulative mastermix of 24.5 μl. The Qiagen multiplex kit mastermix (Qiagen, Hilden, Germany) was used at 12.5 μl, primer mix at 2.5 μl (Primer concentrations were 2 mM of Cest1-4 and 16 mM of Cest5 in Tris-EDTA or water) and nuclease-free water at 9.5 μl constituted as per manufacturer’s instruction. The PCR assay settings were as follows: an initial denaturation step at 94°C for 15 min, followed by 40 cycles at 94°C for 30 s, 58°C for 90 s, 72°C for 10 s, and a final extension at 72°C for 7 min. To visualize the amplicons, PCR products were analyzed by electrophoresis in 2% (w/v) agarose gels for 60 min at 120 V, followed by ethidium bromide staining for 20–30 min and photography under UV illumination. This process was repeated for all loaded gels. Digital photos of the results were saved for later interpretation.
Sarcocystis spp. multiplex polymerase chain reaction
All previously isolated DNA was subjected to a Sarcocystis spp. multiplex PCR targeting the 18S ribosomal RNA (18S rRNA) gene sequences and the mitochondrial cytochrome c oxidase subunit I (COI) gene. The protocol utilized was adapted from Rubiola et al. (Reference Rubiola, Civera, Ferroglio, Zanet, Zaccaria, Brossa, Cipriani and Chiesa2020). The multiplex PCR was capable of detecting S. hominis, S. cruzi, S. hirsuta, S. bovifelis, and Sarcocystis spp. The anticipated fragment sizes for different organisms in the DNA analysis are as follows: 108 bp for S. hirsuta, 200–250 bp for Sarcocystis spp (these were further analyzed via sequencing), 300 bp for S. cruzi, 420 bp for S. hominis, and 700 bp for S. bovifelis. The primers used were 5’-AACCCTAATTCCCCGTTA-3’(Sarco_Rev), 5’-TGGCTAATACATG CGCAAATA-3’ (SarF), 5’-CATTTCGGTGATTATTGG -3’(Hirsuta), 5’-ATCAGATGAAAATCTACTACATGG-3’(Cruzi), 5’-AATGTGGTGCGGTATGAACT-3’(COI_HB), 5’-GGCACCAACGAACATGGTA-3’(COI_H), and 5’-TCAAAAACCTGCTTTGCTG-3’(COI_B). The amplification mixture volume per reaction was constituted to a total of 25 μl. A DNA template of 2.5 μl was mixed with a cumulative mastermix of 22.5 μl (12.5 μl Taq DNA polymerase, 6 μl nuclease free water, Sarco-Rev 1 μl, all other primers at 0.5 μl (Primer conc. 0.5 μM in all, except Sarco-Rev at 1 μM)). The PCR assay involved a denaturation step at 95°C for 3 min, followed by 35 cycles at 95°C for 60 s, 58°C for 60 s, and 72°C for 30 s and a final extension at 72°C for 3 min. PCR products were analyzed by electrophoresis in 2% (w/v) agarose gels for 70 min at 120 V, followed by ethidium bromide staining for 20–30 min and photography under UV illumination.
Sequencing
PCR products were sent for sequencing at Eurofins Genomics in Ebersberg, Germany. Primer Cest5seq was used for sequencing PCR products from the Echinococcus-Taenia spp. multiplex PCR (Trachsel et al. Reference Trachsel, Deplazes and Mathis2007) and primer Sarco-Rev was used for sequencing PCR products from Sarcocystis spp. multiplex PCR (Rubiola et al. Reference Rubiola, Civera, Ferroglio, Zanet, Zaccaria, Brossa, Cipriani and Chiesa2020). DNA sequences were first viewed and manually edited using GENtle v. 1.9.4 (http://gentle.magnusmanske.de). The sequences were identified by comparing with those available in the National Centre for Biotechnology Information database using the basic local alignment search tool (http://www.ncbi.nlm.nih.gov/BLAST/) (Altschul et al. Reference Altschul, Madden, Schäffer, Zhang, Zhang, Miller and Lipman1997).
Data handling and analysis
The data were entered in a Microsoft Excel spreadsheet, cleaned, and validated to check for any errors and omissions. Data were exported to the computer package R version 4.3.1 for analysis. Data on the meat inspection and PCR findings were summarized as proportions and presented in tables.
Results
Bovine cysticercosis detection in abattoirs
During the abattoir survey, 573 randomly sampled bovine carcasses from 10 slaughter facilities were partially inspected for T. saginata cysticerci. The estimated overall prevalence in the study area was 5.4 % (95% CI, 3.8, 7.6). All positive carcasses came from Narok Town Ward, which hosts most (40%) of the surveyed slaughter facilities and carcasses inspected (59%). The aggregate prevalence for Narok Town Ward was 9.1% (95% CI, 6.5–12.7, n = 339). Narok Town Ward had a significantly higher prevalence than Mulot Ward, which had a prevalence of 0% (95% CI, 0–2, n = 187) denoting non-overlapping confidence intervals of the point prevalence for bovine cysticercosis reported in the respective Wards.
The final sampling frame and proportion of positive carcasses per facility are shown in Table 1.
Table 1. The prevalence of bovine cysticercosis in abattoirs, Narok County, April to July 2021
Intensity of infection
Of the 31 infected carcasses, 10 had viable cysts, and 21 had degenerated cysts. One (1/31) infected carcass had both viable and degenerated cysts. Most (24/31) infected carcasses had a single cyst. A total of 14 viable cysts were recovered from one carcass. The mean number of cysts per infected carcass was 1.6 ≈ 2. A total of 51 cysts were recovered from 31 infected carcasses; 25 were viable, and 26 were degenerated.
Molecular detection
All samples were analyzed with PCR-RFLP, whereby 26/31 samples presented a clear T. saginata profile on nPCR. Five samples gave an unclear profile and further tested negative for T. saginata on RFLP. Additional testing gave positive Taenia spp. results on these five samples (Echinococcus spp.-Taenia spp. multiplex PCR). Taenia saginata was detected in 9/10 viable cysts and 17/21 degenerated cysts. Sarcocystis spp. was detected in 9/31 samples. A summary of the findings is in Table 2.
Table 2. Parasites identified from cattle tissue cyst material using various molecular tools
Sequencing
Two PCR products were sequenced and identified as T. saginata and S. hominis. The T. saginata isolate sequence was deposited in the GenBank under accession number OR594291 and was 100% identical to several sequences including that of accession number NC_009938 (Jeon et al. Reference Jeon, Kim and Eom2007). The S. hominis sequence was short (161 bp) and therefore not deposited into the GenBank; it was 100% identical to sequence accession number OQ184854 (Dini et al. Reference Dini, Caffara, Jacinto, Benazzi, Gentile and Galuppi2023).
Discussion
The prevalence of bovine cysticercosis in Kenya has shown varying trends over time and across regions. The documented bovine cysticercosis prevalence estimate in the Narok area prior to this study was 31% (Onyango-Abuje et al. Reference Onyango-Abuje, Nginyi, Rugutt, Wright, Lumumba, Hughes and Johnstone1996b). A report by Asaava et al. (Reference Asaava, Kitala, Gathura, Nanyingi, Muchemi and Schelling2009) demonstrated a lower estimate (3.2%), although this was in a different area – Northern Turkana. An occurrence of 5.4 % determined by incision of the Triceps brachii only was reported. The findings indicate a lower value than the previous estimates for Narok area; however, the study employed detection via the incision of a sole predilection site. Multiple studies have highlighted that meat inspection significantly underestimates the true prevalence, and those studies are based on a much more in-depth dissection of predilection sites (Onyango-Abuje et al. Reference Onyango-Abuje, Nginyi, Rugutt, Wright, Lumumba, Hughes and Johnstone1996b; Minozzo et al. Reference Minozzo, Gusso, de Castro, Lago and Soccol2002; Wanzala et al. Reference Wanzala, Onyango-Abuje, Kang’ethe, Zessin, Kyule, Baumann, Ochanda and Harrison2003; Lopes et al. Reference Lopes, Santos, Soares, Nunes, Mendonça, de Lima, Sakamoto, Costa, Thomaz-Soccol, Oliveira and Costa2011; Jansen et al. Reference Jansen, Dorny, Berkvens, Van Hul, Van den Broeck, Makay, Praet, Eichenberger, Deplazes and Gabriël2017). The true prevalence of bovine cysticercosis in Narok area may therefore be higher.
Inter-ward prevalence comparison was limited in Sogoo, Ololulunga, Keekonyokie, and Mosiro Wards due to the small number of carcasses sampled. Bovine cysticercosis was detected in Narok Town Ward, while no occurrences were reported in Mulot Ward. Narok Town Ward hosts a relatively higher concentration of pastoralists who source cattle locally when compared to Mulot Ward (NCG 2016). Thitu et al. (Reference Thitu, Kaseje and Augustine2016) indicated that members of this pastoralist community exercise risky practices such as open defecation. Consumption of raw/partially cooked meat is also common (Chege et al. Reference Chege, Kimiywe and Ndungu2015). It is noteworthy that Narok County supplies meat to far-flung markets beyond its borders (Mwangi et al. Reference Mwangi, Owuor, Kiteme and Giger2020) and is therefore of significant spatial consideration in the control of T. saginata taeniasis in other parts of Kenya. Due to its proximity to the neighbouring Bomet County, Mulot SH (Mulot Ward) sources most of its slaughter cattle from Bomet County (pers. comm). Notably, Bomet County has higher improved water, sanitation coverage, and literacy rates when compared to Narok County (74%, 78%, and 83% in Bomet County compared to 35%, 20%, and 53% in Narok County) (KNBS 2019).
An average of 1.6 ≈ 2 cysticerci per infected carcass was found, based on incisions in one muscle. Minozzo et al. (Reference Minozzo, Gusso, de Castro, Lago and Soccol2002) estimated that for each cysticercus found on routinely inspected tissues, there are at least 6.1 that remain undetected. Meat inspection positivity is therefore only an indicative underestimate. One carcass harboured 14 viable cysts (27% of the total cysts retrieved). The high intensity of infection insinuates a compromised immunity (OIE 2021) or possibly a case of recent exposure to a high number of viable T. saginata eggs. Notably, however, a high count of viable cysts is a common finding in carcasses from young animals (Froyd Reference Froyd1960; Wanzala et al. Reference Wanzala, Onyango-Abuje, Kang’ethe, Zessin, Kyule, Baumann, Ochanda and Harrison2003; OIE 2021). Such carcasses are potential ‘super-spreaders’ and pose a relatively higher public health risk where meat inspection is not conducted. Most of the infected carcasses had degenerated cysts (22/31, 71%). This is consistent with other reports (Jansen et al. Reference Jansen, Dorny, Berkvens, Van Hul, Van den Broeck, Makay, Praet, Eichenberger, Deplazes and Gabriël2017; OIE 2021).
The meat inspection regulation in Kenya outlines a few predilection sites to detect T. saginata cysticerci (Cap 356 of the Meat Control Act). It directs the meat inspector to examine the tongue, masseter muscles, Triceps brachii, heart, and diaphragm, but it mentions that the inspector has the liberty to proceed with further incisions at predilection sites if there is suspicion of bovine cysticercosis. It also gives guidance on carcass treatment and handling relative to the intensity of infection (Meat Control Act 2012). An observation made in the context of routine surveillance for bovine cysticercosis was that the major predilection sites inspected were the triceps muscles in both forelimbs and the heart. In the event of positive findings on the two sites, seldom were additional incisions made. Information on infection intensity was not commonly captured possibly due to the absence of infrastructure to support carcass treatment. The observed practices were that of excision of affected tissue and therefore a risk of releasing unsafe meat to the public.
Molecular tools were able to amplify and detect parasite DNA from all 31 cyst tissues despite 21/31 of the cysts being classified as degenerated. PCR-RFLP (Geysen et al. Reference Geysen, Kanobana, Victor, Rodriguez-Hidalgo, De Borchgrave, Brandt and Dorny2007) was able to confirm T. saginata larvae in 26/31 (84%) of the cysts, and 5 samples were noted as ‘positive but doubtful’ from the assessment of results from the genus-specific nested PCR. This was due to the presence of a slightly lighter band than Taenia spp. positive control samples and other positives (i.e., 750–775 bp instead of 798 bp). These samples were negative for T. saginata during post PCR- RFLP with Ddel, Hinfl, and Hpal enzymes. The 5 samples were, however, positive for Taenia spp. in the Echinococcus spp.-Taenia spp. multiplex PCR (Trachsel et al. Reference Trachsel, Deplazes and Mathis2007), which is genus-specific for Taenia spp. These findings suggest the presence of other Taenia spp. as a cause of bovine cysticercosis in Kenya. Sequencing analysis will, however, be required to confirm the identity of the taeniid. Hailemariam et al. (Reference Hailemariam, Nakao, Menkir, Lavikainen, Iwaki, Yanagida, Okamoto and Ito2014)) reported non-T. saginata cysticerci parasitizing cattle in Ethiopia and hypothesized that the parasite could be T. hyaenae. The sampled carcasses are from cattle owned by pastoral communities that have close interactions with wildlife, exposing them to taeniids from the wild.
This is the first report and molecular confirmation of S. cruzi and S. hominis in Kenya. Concurrent infection by S. cruzi and T. saginata (6/31) and T. saginata and S. hominis (1/31) was also confirmed. Sarcocystis cruzi and S. hominis are microscopic intracellular parasites (Dubey Reference Dubey2015). Infected muscle tissue adjacent to the cyst wall was likely included during the DNA extraction procedure. Most of the Sarcocystis spp. positive DNA samples (8/9) were also derived from degenerated cyst lesions. The chronic inflammatory response around the cysticerci wall may have increased the likelihood of inadvertently including infected muscle tissue due to its adhesion to the surrounding structures, attributed to collagen infiltration (Dini et al. Reference Dini, Caffara, Jacinto, Benazzi, Gentile and Galuppi2023).
Previous reports on bovine sarcocystosis in the country are limited. The scarcity of published literature in Kenya on sarcocystosis implies a low research focus consequently leading to potential latent economic losses and health implications. This is corroborated by the confirmation of infection in various livestock including cattle in other African countries such as Egypt (Ahmed et al. Reference Ahmed, Elshraway and Youssef2016; El-Kady et al. Reference El-Kady, Hussein and Hassan2018; Gareh et al. Reference Gareh, Soliman, Saleh, El-Gohary, El-Sherbiny, Mohamed and Elmahallawy2020; El-Morsey et al. Reference El-Morsey, Abdo, Zaid and Sorour2021), Algeria (Taibi et al. Reference Taibi, Benatallah, Zenia, Aissi, Harhoura, Milla, Guerchaoui, Kaabeche and Khodja2020), Ethiopia (Mekibib et al. Reference Mekibib, Abdisa, Denbarga and Abebe2019), Tunisia (Amairia et al. Reference Amairia, Amdouni, Rjeibi, Rouatbi, Awadi and Gharbi2016), and Nigeria (Obijiaku et al. Reference Obijiaku, Ajogi, Umoh, Lawal and Atu2013). This assertion considers the parasite’s relatively high occurrence in the screened samples (29%) despite the survey design not being optimized to detect Sarcocystis spp. Sarcocystis cruzi in cattle seldom manifests with a severe syndrome but is nonetheless associated with BEM, a cause of economic losses due to carcasses condemnation (Dubey Reference Dubey2015; Castro-Forero et al. Reference Castro-Forero, Bulla-Castañeda, López Buitrago, Díaz Anaya, Madeira de Carvalho and Pulido-Medellín2022; Dini et al. Reference Dini, Caffara, Jacinto, Benazzi, Gentile and Galuppi2023; Dubey and Rosenthal Reference Dubey and Rosenthal2023). Sarcocystis infection due to S. hirsuta can confound T. saginata cysticerci, leading to false positives during routine meat inspection (Dubey et al. Reference Dubey, Udtujan, Cannon and Lindsay1990; Ogunremi et al. Reference Ogunremi, MacDonald, Geerts and Brandt2004). Cattle infections with zoonotic S. hominis have been reported in Algeria (Nedjari Reference Nedjari2003; Taibi et al. Reference Taibi, Benatallah, Zenia, Aissi, Harhoura, Milla, Guerchaoui, Kaabeche and Khodja2020), Tunisia (Amairia et al. Reference Amairia, Amdouni, Rjeibi, Rouatbi, Awadi and Gharbi2016), and Nigeria (Obijiaku et al. Reference Obijiaku, Ajogi, Umoh, Lawal and Atu2013). Sarcocystis hominis infections in cattle are associated with environmental contamination due to open defaecation, similar to bovine cysticercosis (Castro-Forero et al. Reference Castro-Forero, Bulla-Castañeda, López Buitrago, Díaz Anaya, Madeira de Carvalho and Pulido-Medellín2022). Conducting further investigations into the epidemiology of sarcocystosis in Kenya is crucial to preventing human infections and minimizing economic losses within the beef industry.
Conclusion
Study findings point towards the persistence of bovine cysticercosis in cattle within the study area with hot spots in Narok Town Ward. Further investigations are required to reveal source villages/sub-locations for targeted control efforts. The cystic lesions were confirmed to be T. saginata cysticerci via molecular methods, which also revealed the possibility of other Taenia spp. being responsible for bovine cysticercosis in the study area. The presence of bovine cysticercosis suggests suboptimal sanitation practices, which may include open defecation due to the lack of toilets/pit latrines, the persistence of tribal taboos that discourage toilet use, and inadequate meat inspection protocols. Additionally, culinary habits such as consuming raw or partly cooked beef may be practiced in the area, potentially facilitating transmission.
Consequently, it is imperative to invest in initiatives aimed at reducing the transmission of T. saginata. Interventions at the slaughterhouse level may involve upgrading facilities to treat infected carcasses and enforcing strict adherence to the inspection regulations. On the community level, interventions include education on the prevention and control of T. saginata taeniosis; improving water, sanitation, and hygiene capacity; and ensuring proper cooking of meat. These measures can then be supported by diligently monitoring infection in cattle.
This is the inaugural report on Sarcocystis spp. infection in cattle in the country. Disseminating information regarding the presence of sarcocystosis in the Kenyan cattle population to meat inspectors, coupled with capacity building on its detection, is imperative. Other facets of the national veterinary health system could then look into comprehensive surveillance that will inform effective disease management, mitigation of production losses, and integration into disease control initiatives. The zoonotic nature of S. hominis and T. saginata necessitates a One Health approach in both surveillance and control.
Acknowledgements
We express our gratitude to the veterinary department of the County Government of Narok for their invaluable support during data collection. Special thanks go to Tabitha Irungu, Zipporah Gitau, and Sandra Vangeenberghe for their technical assistance. We also acknowledge Maasai Mara University for granting study leave to facilitate part of the laboratory work.
Financial support
Molecular diagnostics for this study was supported by the Global Minds Fund-Short Research Stay 2022/2023 scholarship from the University of Ghent (grant GMF.SRS.2022.0001.01.).
Competing interest
The authors declare none.
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