Prevalence of subclinical mastitis, its associated bacterial isolates and risk factors among cattle in Africa: a systematic review and meta-analysis

BACKGROUND

Subclinical mastitis (SCM) is one of the most economically important diseases affecting the dairy industry. The SCM does not cause visible changes in the udder or physical changes of the milk as compared to clinical mastitis, and a clear overview of the prevalence and risk factors in the different regions of Africa is still lacking. The objective of this study was to investigate the prevalence of SCM and assess the associated risk factors and dominant bacterial pathogens among cattle in Africa.

MATERIALS AND METHODS

We gathered and systematically reviewed literature concerning SCM, published in English from January 2010 through December 2020 in two databases (PubMed and Web of Science), and meta-analysis was conducted using the 'meta' and 'metafor' packages in the R statistical software.

RESULTS

A total of 258 studies were retrieved and at the end of the screening, 82 full-texts were eligible for inclusion in the meta-analysis. The prevalence of SCM was reported in 11 countries in five regions of Africa, and the random-effects model showed that the weighted pooled prevalence estimate (PPE) was 48.2% (95% CI: 43.6-52.8%). Heterogeneity was high and statistically significant as I2 (proportion of observed variation) was 98.1% (95% CI: 98.0-98.3%), τ2 (true between-study variance) was 0.0433 (95% CI: 0.0322-0.0611), and the Cochran Q statistic was 4362.8 (p < 0.0001). Subgroup and meta-regression analyses showed that East Africa had significantly (p = 0.0092) the highest PPE of SCM (67.7%, 95% CI: 55.7-78.7) followed by West Africa (50.5%, 95%CI: 31.4-69.5), and the lowest was in North Africa (40.3%, 95%: 32.2-48.6). Other significant moderators for SCM were age (p < 0.0001), breed (p = 0.0002), lactation stage (p = 0.019) and parity (p = 0.0008) of cattle. Staphylococcus species (prevalence 43.7%) were the most predominant pathogens, followed by Streptococcus (18.2%) and Escherichia species (9.5%).

CONCLUSION

The present study showed a high variation of SCM prevalence in various parts of Africa, although there is a need for more data in some regions. The reported prevalence is a clear sign of inappropriate management practices among cattle herds and an indicator of the threat that SCM poses to the dairy industry. The information about the predisposing factors may guide effective management and control strategies to reduce transmission of the disease.

Intramammary treatment using allogeneic pure platelet-rich plasma in cows with subclinical mastitis caused by Gram-positive bacteria

The aims of the study were (1) to compare the cure risk of intramammary treatment of pure platelet rich plasma (P-PRP) or cefquinome sulfate (CS) in cows with subclinical mastitis (SCM) caused by Gram-positive bacteria, evaluated via somatic cell count (SCC) and the microbiological analysis of milk; (2) to compare the inflammatory/anti-inflammatory response of mammary gland to both treatments through the analyses of interleukins (IL), interferon gamma (IFN-γ), and tumour necrosis factor alpha (TNF-α) in milk. A non-inferiority randomized clinical trial was conducted. The null hypothesis was that cure risk in the experimental group (P-PRP) was inferior to the reference group (CS). A total of 103 cows were selected according to SCC and presence of Gram-positive bacteria, 49 cows were treated with CS and 54 cows were treated with P-PRP after determination of its cellular and molecular quality control. Cure was assessed by milk analyses at day 21 and 22 after treatment. Cows that remained with SCM were retreated at day 26, and cure assessed at day 47 and 48. Overall, bacteriological cure was observed in 16 cows (30%) of the P-PRP group, and 35 cows (71%) in CS group. Staphylococcus aureus cure risk was higher in CS group, but inconclusive for Streptococcus spp. The mean SCC increased in relation to time only in the P-PRP group. A direct relation between time and treatment for IL-1, IL-2, and IL-6 was observed, while no differences were observed for IL-4. Furthermore, IL-1 and IL-2 increased in cows treated twice in both groups. IL-8, IFN-γ, and TNF-α showed a significant interaction between time and treatment. IFN-γ concentration was lower in the P-PRP group compared to the CS on days 0 and 22. Leukocyte counts were lower in P-PRP when compared to whole blood. TGF-β1 and PF4 concentrations were higher in platelet lysates in comparison to P-PRGS and plasma. Moreover, PDGF-BB concentration was significantly higher in platelet lysates in comparison to plasma. Results obtained in this study demonstrate that SCM treated with PRP showed a lower rate of bacteriologic cure when compared to animals treated with CS.

Prevalence of bovine mastitis and main risk factors in Tunisia

Tunisian milk chain is in danger with a dramatical reduction of milk production over the last years. Improving the quality of milk seems mandatory to improve farmers' income, but for the moment, there is only scarce data on milk quality management in Tunisia. In this context, the aims of our study were first to describe the prevalence of bovine mastitis in 267 cows from 71 representative small dairy farms in the North (43.7%) and Center (56.3%) regions of Tunisia, using mastitis detection by California Mastitis Test (CMT) on milk quarter and clinical signs, and second, to assess possible risk factors for mastitis from animal, environment, and breeding management. In parallel, cow and bulk milk somatic cell count (SCC) were analyzed. Our results demonstrated that 60.3% of cows showed mastitis as determined by CMT and clinical examinations. Increased stage of lactation, parity, udder depth, and type of milking were significantly (P < 0.05) associated with increased odds of mastitis prevalence. The mean of individual cow SCC (ISCC) and bulk milk SCC (BMSCC) was very high (1083 × 10³ cells/mL and 698 × 10³ cells/mL, respectively), all ranks and stages of lactations combined. These high values confirm the infectious origin of mastitis that we found caused mainly by Staphylococcus aureus and coagulase-negative Staphylococci. In conclusion, control of the identified risks factors and improved biosecurity measures must be encouraged to restore udder health and milk quality and thus productivity and durability of Tunisian milk chain.

Identification of staphylococci causing mastitis in dairy cattle from Algeria and characterization of Staphylococcus aureus

AIMS

This study was conducted to determine the occurrence of staphylococci from cows with subclinical mastitis from independent herds in Algeria, and to characterize Staphylococcus aureus isolates.

METHODS AND RESULTS

Quarter milk samples were collected separately, somatic cells were counted and samples with more than 200 000 somatic cells per ml were cultured on blood agar. Staphylococci isolates were identified by routine diagnostics, and S. aureus isolates were tested for antibiotic susceptibility by disk diffusion and microdilution. Congo red agar was used to detect biofilm formation and capsule synthesis was detected on serum soft agar (SSA). The S. aureus isolates were characterized by spa typing. DNA microarray analysis was performed to detect resistance and virulence genes. Overall, 40·0% (167/418) of the cows suffered from mastitis. In 63·5% (106/167) of the cows staphylococci were identified. Nine of the 106 Staphylococcus isolates (8·5%) were S. aureus. The coagulase-negative staphylococci belonged to 14 species. All S. aureus isolates were multiresistant and biofilm forming, with 66·67% of them showing diffuse colonies on SSA and belonged to CC97-agrI-cap5. Biofilm genes (icaA/C/D), 13 genes encoding for adhesion, six genes encoding proteases, 11 genes encoding superantigen like toxins were found. Genes conferring resistance to tetracycline (tet(K)), penicillin (blaZ/I/R) and macrolide-lincosamide-streptogramin B (erm(B), erm(A)) were also detected in the S. aureus from this study.

CONCLUSIONS

The current investigation provides a detailed molecular and biofilm formation ability of S. aureus involved in subclinical mastitis in Algeria and shows the wide distribution of adhesion and enterotoxin(-like) genes among S. aureus responsible for causing subclinical bovine mastitis.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings are valuable in tracking the evolution and genomic variation of S. aureus from bovine origin.

Epidemiological investigation of subclinical bovine mastitis in Algeria and molecular characterization of biofilm-forming Staphylococcus aureus

Thirty dairy farms were selected for this study; the first objective of our study was to investigate the prevalence of subclinical bovine mastitis (SCM) in Eastern Algeria, from 600 lactating cows, and to identify potential risk factors associated with the occurrence of bovine mastitis and bacteria isolation using logistic regression. The second objective was to evaluate biofilm formation capacity and detect biofilm-associated genes of S. aureus, isolated from SCM cases. Molecular typing was investigated by spa typing. The prevalence of mastitis at cow and quarter level was 37.66% (226/600) and 27.17% (555/2042), respectively. Stage of lactation, cow breed, milk production, and the study area were factors associated with SCM. In addition, the most frequent pathogens isolated from mastitic milk were coagulase-negative staphylococci (CNS), E. coli, and S. aureus. The study area was highly associated with SCM caused by S. aureus; cows from Setif province were 18 times more affected with SCM caused by S. aureus compared to cows from Batna province (OR = 18.6, 95%CI 2.038-171.2), but were less affected with SCM caused by CNS isolates (OR = 0.17, 95%CI 0.033-0.868). Moreover, cows with milk production less than 10 L per day increased (p < 0.05) the prevalence of mastitis caused by E. coli. All the S. aureus isolates had biofilm-forming ability, and 41.66% of isolates were positive for adhesion genes (icaA, icaD, fbnA, and clfA). This study, therefore, warrants the need for improving sanitary measures and strict hygienic measures, and presents the first insight into biofilm-forming ability of S. aureus strains causing mastitis in dairy herds in Algeria, which will help in tracking the evolution of epidemic strains responsible for causing bovine mastitis.

Prevalence and etiology of mastitis in dairy cattle in El Oro Province, Ecuador

This study described the occurrence of clinical and subclinical forms of mastitis in 250 cattle from 5 dairy farms around the cities of Santa Rosa and Machala, El Oro Province, Ecuador. Clinical mastitis (CM) was determined based on obvious changes in milk (mild), signs of inflammation in the udder (moderate), and/or generalized clinical symptoms (severe). Subclinical mastitis (SCM) was assessed using the California mastitis test. CM and SCM were detected in 30 (12.0%) and 150 (60%) of the 250 tested cattle, respectively. Prevalence at the udder quarter level was 57.7% (577/1,000), which was higher among forequarters (369/577; 63.9%) than hindquarters. Of the 577 mastitic milk samples subjected to microbiological analysis, 35 were excluded due to contamination and 20 tested negative. Identification of bacterial isolates revealed that 33.3% of the 93 CM samples contained coliforms, 25.8% coagulase-positive staphylococci, 20.4% coagulase-negative staphylococci (CNS), 9.7% streptococci, 7.5% Bacillus spp., and 3.2% Klebsiella spp. Bacterial profiling of the 429 SCM milk samples showed that 55.4% contained CNS, 22.1% Bacillus spp., 9.3% streptococci, and 6.1% coagulase-positive staphylococci. In vitro antibiotic susceptibility testing of the obtained isolates indicated that all were susceptible to amoxicillin, ampicillin, cefotaxime, enrofloxacin, sulfamethoxazole-trimethoprim, gentamicin, and neomycin. No multidrug-resistant strains were observed.

Importance of bovine mastitis in Africa

Bovine mastitis is an important animal production disease that affects the dairy industry globally. Studies have estimated the prevalence of this disease in approximately 30% of African countries, with the highest prevalence found in Ethiopia. This is despite the wide cattle distribution in Africa, and the largest number of dairy farms and herds in countries such as South Africa, Kenya and Uganda. Furthermore, the estimated financial losses due to direct and indirect impacts of bovine mastitis are lacking in this continent. Therefore, intensive research efforts will help determine the continent-wide economic impacts and advance careful monitoring of disease prevalence and epidemiology. Here, published cases supporting the occurrence and importance of bovine mastitis in certain regions of Africa are outlined.