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 JBM  Vol.9 No.3 , March 2021
Seroprevalence of Brucella Antibodies and Risk Factors Associated with Human Brucellosis in High-Risk Occupational Groups of the Noun Division in the West Region of Cameroon
Abstract: Brucellosis is an anthropozoonotic disease with an important public health impact. Although the transmission of Brucella from animals to humans can occur in different epidemiological settings of sub-Saharan African countries, little data has been published on human brucellosis. This study aimed to detect Brucella antibodies and the risk factors associated to brucellosis among high-risk occupational groups of people in the Noun Division of Cameroon. For this study, a structured questionnaire was used to assess risk factors associated with human brucellosis. Thereafter, blood samples were collected from high-risk occupational groups of people in four villages. Plasma was extracted from each sample and Brucella antibodies were detected using Rose Bengal Plate Test (RBPT) and indirect Enzyme-Linked Immunosorbent Assay (i-ELISA). Of the 273 participants enrolled, the overall seroprevalence of Brucella antibodies was 12.45% with RBPT and 10.26% with i-ELISA test. This seroprevalence was significantly (P = 0.04; X2 = 9.73) higher among livestock herdsmen (15.8%), slaughterhouse workers (9.8%), butchers (4.8%), participants having no educational level (14.3%) and those experiencing above 5 years of risky activity (15%). Raw milk consumption (OR: 4.8; P = 0.001), no formal education (OR: 6.4; P = 0.03) and assistance of animal during parturition (OR: 7.2; P < 0.0001) appeared as factors that may increase the risk of Brucella infections. The detection of Brucella antibodies indicates the risk of human brucellosis in some groups of people of the Noun division. Consuming unpasteurized milk, participating in parturition and lacking knowledge on brucellosis appeared as risk factors associated with human brucellosis in western Cameroon. It raises the need of developing and implementing control measures for human and animal brucellosis.

1. Introduction

Brucellosis is an infectious and contagious zoonotic disease classified among the top seven neglected bacterial disease of both humans and animals [1] [2]. It is caused by bacteria of the genus Brucella. Different Brucella species, including Brucella abortus,Brucella melitensis,Brucella suis,Brucella ovis andBrucella canis, are responsible for brucellosis in animals and humans [3]. These bacteria are transmitted to humans through the consumption of infected and unpasteurized dairy products or by direct contact with infected animal secretions and excreta [4]. Brucellosis induces important socio-economic impacts and constitutes a serious public health threats for humans and animals. As a neglected zoonotic disease, less attention is given to it by scientists and stakeholders, especially in low-income countries [5].

Brucellosis is one of the major constraints of livestock productivity with significant economic losses estimated yearly to about 427 million US$ in sub-Saharan Africa [1] [6] [7]. Many studies undertaken to generate epidemiological data on brucellosis have been focused on Brucella antibodies in various animal species [8] [9] [10] [11] [12]. In these studies, the seroprevalence of Brucella antibodies ranges from 3% to 41% [12] [13]. These variations were observed within and between African countries. In Cameroon for instance, Kamga et al. (2020) [14] have recently reported some variations in the seroprevalence of Brucella antibodies in domestic animals according to agro-ecological zones, highlighting the circulation of Brucella species in different agro-ecological settings. In addition, the presence of Brucella antibodies in livestock indicates the transmission ofBrucella to different animal species and probably to humans; pointing out the risk of human brucellosis in Cameroon like in many developing countries. As the risk of human brucellosis depends of the livestock diseases and also the contact frequency between human and livestock, the detection of Brucella antibodies in animals of many sub-Saharan countries suggests possible transmission of Brucella to humans.

Human brucellosis is characterized by non-specific symptoms such as undulating fever, fatigue, headache, backache, joint pains, musculo-skeletal pains, sweating, arthralgia, malaise and body wasting [15]. These non-specific signs make the clinical diagnosis of brucellosis challenging in sub-Saharan Africa due to misdiagnosis to malaria or other infectious diseases [15] [16]. Globally, an estimate of 500,000 new cases and 25,000 deaths due to Brucella infections occur every year [17] [18]. Although sporadic cases of brucellosis are often reported in some sub-Saharan African countries, its prevalence may reach 41% in some areas [12] [19] [20] [21]. However, it is important to point out that many human brucellosis cases can pass undetected due to the lack of surveillance program in many sub-Saharan countries [22]. Raising awareness for the design and implementation of control program for humans and animal brucellosis requires generating data on Brucella infections in both human and animals. Data already generated on the seroprevalence of Brucella antibodies in animals indicate the risk of human brucellosis in many sub-Saharan countries. In Cameroon, little investigations have been undertaken on humans’ brucellosis [23]. Investigations performed on abattoir workers of the Adamawa and East regions of Cameroon reported a seroprevalence of Brucella antibodies of 12.15% and 28.10% respectively [24] [25]. The difference observed in this seroprevalence suggests that the risk of human brucellosis could vary according to epidemiological settings. Understanding the real epidemiological situation of human brucellosis may require additional studies and data within different epidemiological settings. In this framework, estimating the contact or the seroprevalence of Brucella antibodies in humans, especially in people who are regularly in close contact with livestock or derived products, constitutes one step of the process that will help to understand the epidemiological situation of brucellosis in each setting. Moreover, knowledge on the risk factors associated with brucellosis could also help to understand the transmission of Brucella and to design control measures for this neglected zoonotic disease.

This study was designed to determine the seroprevalence of Brucella antibodies and risk factors associated with Brucella infections among high-risk occupational groups of people of the Noun division in the west region of Cameroon.

2. Material and Methods

2.1. Study Area and Study Population

The study population was individuals performing activities that exposed them to the risk of acquiring Brucella infections [26] [27]. For this study, the activities considered as high-risk factors for human brucellosis are livestock herdsmen, butchers, slaughterhouse’s workers, veterinarians, meat and milk sellers. People performing these activities are considered as high-risk occupational groups (HROG) for brucellosis.

This study was performed in the Noun Division of Cameroon. It is a semi-rural zone with an estimated population of 434,542 inhabitants. It covers about 7687 km2 with a vegetation characterized by savannah and degraded forest [28]. The sampling was done at Magba (5˚57'00N; 11˚13'00E), Koutaba (5˚42'29N; 10˚41'02), Foumbam (5˚43'N; 10˚55'E) and Massangam (5˚25'29'N; 11˚0'1E) (Figure 1). The division has a dense hydrographic network with many streams, rivers and dams rendering the locality a suitable transhumance area for farmers

Figure 1. Map of the Noun division showing villages where samples were collected (Map created with QGIS v. 3.8 software (https://www.qgis.org).

during the dry season. Inhabitants of the Noun division practice agriculture, trade, breeding of cattle and small ruminants. In most villages, human/livestock contacts are common. Foumban which is the head-quarter of the Noun Division is the most populous village with an estimated population of 106,309 inhabitants [29]. The main slaughterhouse and cattle market of the Noun division is located at Foumban. Recently, Kamga et al. (2020) [14] reported Brucella antibodies in several domestic animal species of this locality.

2.2. Ethics Approval and Consent to Participate

The protocol of this study was approved by the Ethical Committee of the Ministry of Public Health of Cameroon of the 23 October 2018 with reference number N˚2018/10/1117/CE/CNERSH/SP. The local administrative and traditional authorities of each sampling site were also informed and gave their approval. Subsequently, the review board of the Molecular Parasitology and Entomology Sub-Unit of the Department of Biochemistry of the Faculty of Science of the University of Dschang gave their approval. Informed consent was written because each adult enrolled in this study gave its approval by signing an informed consent form and a Certificate of Confidentiality. For all participants below 18 years, the written informed consent was obtained from their parents or guardians. Moreover, a signed assent form was also obtained from participants of 10 to 17 years. During the analyses, data for each participant were anonymized.

2.3. Sampling Size Estimation and Questionnaire Survey

The sample size was estimated using a cross-sectional studies formula as described by [30]:

n = Z 2 P exp ( 1 P exp ) / L 2

where:

n: is the minimum sample size required;

Z: is the critical value for a given confidence interval which is 1.96 at 95% confidence interval;

P: is the expected prevalence;

L: is the margin of error (the margin of error is 0.05).

To estimate this sample size, a human brucellosis prevalence of 12.5% outlined by [24] in abattoir workers of Ngaoundere in the Adamawa region of Cameroon was used. Based on this, the estimated minimum sample size was 165 individuals. However, a total of 273 participants were enrolled based on their cooperation.

2.4. Recording of Socio-Demographic Factors

For each participant who agreed to participate in this study by signing an informed consent form, socio-demographic parameters and other information related to the risk factors that can be associated with brucellosis were recorded using a structured questionnaire adopted from [31] [32] [33] [34]. The collected information’s were age, sex, professional activities (butcher, veterinarians, meat seller, farmers and livestock keepers), awareness about brucellosis, assistance during animal parturition, knowledge about zoonotic diseases, consumption of raw milk, educational level and longevity in the profession. The questionnaire was translated as needed to local language (Bamoun or Foufoulde) in order to minimize bias by the interviewer.

2.5. Blood Samples Collection and Plasma Preparation

For this cross-sectional study carried-out from October to November 2019, 5 ml of blood sample were collected from each selected participant (high-risk occupational groups). This collection was performed by peripheral vein puncture with disposable needles. The Venoject EDTA-coated tubes containing blood sample were labelled and carefully packed. In the field, blood samples were stored at 4˚C in an electric cooler before being transported to the laboratory where they were stored at 4˚C for less than one week before plasma extraction. Plasma was extracted by centrifugation of each blood tube at 8000 xg for 10 min. Thereafter, 500 µl of plasma was collected from each tube and then, transferred into 2 ml sterile micro-tubes that were subsequently stored at −20˚C until use.

2.6. Detection of Brucella Antibodies

All plasma samples were accurately tested for Brucella antibodies using a combination of two serological tests: the Rose Bengal Plate Test (RBPT) and the indirect Enzyme-Linked Immunosorbent Assay (i-ELISA). The RBPT and the i-ELISA were performed of plasma samples that were stored at −20˚C for less than two months.

2.6.1. Detection of Brucella Antibodies by Rose Bengal Plate Test (RBPT)

The detection of Brucella antibodies in the plasma was performed with the Rose Bengal Plate Test (RBPT) (ID.Vet, Innovative Diagnostics, France) as described by [35]. Briefly, an aliquot of each plasma sample as well as the RBPT reagents were allowed to thaw at room temperature (22˚C ± 4˚C) for approximately 25 minutes as recommended by the manufacturer. Thereafter, 30 μL of plasma and an equal volume of RBPT antigen were put in each circle of the RBPT plate and then mixed. After 4 minutes of rocking the plate at room temperature, the plate was observed by unaided eyes to see if there is any agglutination. Any visible agglutination on the plate by unaided eyes was considered positive; this means that the plasma sample contains Brucella antibodies [36]. If no agglutination was observed, the test was considered negative (no antibodies against Brucella in the plasma tested).

2.6.2. Detection of Brucella Antibodies by Indirect Enzyme-Linked Immunosorbent Assay (i-ELISA)

The i-ELISA test was performed to confirm RBPT results. The i-ELISA tests were performed in a polystyrene plate of 96-wells pre-coated with purified antigens of Brucella spp. Plasma samples were tested for the presence of antibodies against Brucella spp using multi species commercial indirect ELISA test kit (ID-Screen Brucellosis Serum Indirect Multispecies, ID VET, product code BRUS-MS-1014, Gabrels, France) [37]. The tests were performed according to the instructions of the manufacturer (ID-VET, 2008). Before each i-ELISA test, reagents and plasma samples were allowed to thaw at room temperature (22˚C ± 4˚C) and 100 µL of diluted buffer were added to each well. Ten (10 µl) micro-liters of positive control and equal volume of negative control provided by the manufacturer were introduced into two different wells of the plate and 10 µL of each plasma sample were introduced in the remaining wells. Each plate was sealed and manually homogenized gently. After incubation at room temperature for 45 minutes, each plate was washed 3 times with PBS-Tween and 100 µL of multispecies horseradish peroxidase (HRP) conjugate were added to each well. Each plate was subsequently incubated for 30 minutes at room temperature and washed 3 times to eliminate the excess of conjugate. Thereafter, 100 µL of the substrate solution (tetramethylbenzidine in substrate buffer containing H2O2) were added to each well and the plate was incubated in the dark for 15 minutes at room temperature. The reaction was stopped by adding 100 μL of 1 N hydrochloric acid (HCl). The optical density in each well was measured at 450 nm using a micro plate photometer (Bio Tek ELX800 absorbance reader). For each tested sample, its result was expressed as a percentage of optical density (%OD) that was calculated using the following formula:

% OD = 100 × ( S N ) / ( P N )

where S, N and P are ODs of the sample, the negative and positive controls respectively. Sample with a % OD ≥ 120% where considered positive.

2.7. Data Analysis

The Statistical Package for Social Sciences (SPSS), version 21.0, software package was used to perform the statistical analysis of all collected data. Pearson chi-square test was used to compare the seroprevalence of Brucella antibodies between villages, activities performed by participants, sex, age, longevity in the activity and educational school level of the study population. Logistic regression model was used to determine which risk factor is associated with the presence of Brucella antibodies among the study participants. Odds ratio (OR) and 95% Confidence interval (CI) were noted. A p-value below 0.05 was considered as statistically significant.

3. Results

3.1. Socio-Demographic Characteristics of the Study Population

Of the 273 participants enrolled in this study, 186 (68.13%) were from Foumban, 54 (19.8%) from Koutaba, 21 (7.7%) from Magba and 12 (4.4%) from Massangam (Table 1). Among these participants, 101 (36.99%) were livestock keepers/famers, 84 (30.76%) butchers, 61 (22.34%) slaughterhouse workers, 11 (4.03%) veterinarians and 16 (%) meat and milk sellers (Table 1). Sixteen (5.8%) of these participants were female while 257 (94.1%) were males. The mean age of participants was 38.5 ± 14.45 years (inter quartile range (IQR): 15 - 73 years). One hundred and fifty-nine (58.2%) participants attended the primary education, 79 (28.9%) the secondary education and 35 (12.8%) did not have any formal education (Table 1). Two hundred and nine (79.6%) of these participants has expended over 5 years in their occupation (Table 1).

3.2. Prevalence of Brucella Antibodies According to Villages

Figure 2 illustrates results of RBPT where some plasma samples generated agglutinations and other no agglutination. The overall seroprevalence of Brucella antibodies revealed with RBPT and i-ELISA tests was 12.5% (95% CI: 8.6 - 17.4) and 10.3% (95% CI: 6.8 - 14.8) respectively. For subsequent analyses, only participants that were positive for both RBPT and i-ELISA were considered as have been in contact with Brucella or have Brucella antibodies. On this basis, the

Table 1. Prevalence of Brucella antibodies and bivariate analysis of factors associated with human brucellosis amongst the study participants.

N: Number of human samples tested; OR: odds ratio; CI: confident interval; i-ELISA: indirect Enzyme-Linked Immunosorbent Assay; *significant P-value.

Figure 2. Example of Rose Bengal plate Test presenting result obtained after assay of plasma samples: 4, 5 and 9 are spots showing no agglutination reaction (plasma samples that were negative or do not contain Brucella antibodies); 10: spot showing an agglutination reaction (plasma sample that was positive or contains Brucella antibodies).

overall seroprevalence of Brucella antibodies was 9.5%. The highest seroprevalence of Brucella antibodies of 14.3% was recorded in Magba following by Koutaba with 9.5% and Foumban with 9.1%. Massangam had the lowest prevalence of 8.3% (Table 1). No significant difference (P = 0.60; X2 = 0.89) was observed when comparing the seroprevalence of Brucella antibodies between villages (Table 1). Moreover, the OR ranges from 1.1 (95% CI: 0.1 - 10.6) at Koutaba to 1.9 (95% CI: 0.1 - 21.1) at Magba. Whatever the village, no P value was statistically significant (Table 1). This indicates that belonging to any village cannot be considered as risk factors of having Brucella infections.

3.3. Prevalence of Brucella Antibodies According to Participants’ Activities

The seroprevalence of Brucella antibodies in slaughterhouse workers, livestock keepers/herdsmen and butchers were respectively 9.8%, 15.8% and 4.8%. No participant belonging to veterinary staff, meat and milk sellers was found with Brucella antibodies (Table 1). Comparing the seroprevalence of Brucella antibodies according to activities performed by participants, significant difference (P = 0.04; X2 = 9.73) was observed. The ORs were high for livestock keepers/herdsmen (OR = 4.4; 95% CI: 0.2 - 79.0) and slaughterhouse workers (OR = 3.3; 95% CI: 00.2 - 62.3). For butchers and meat or milk sellers, the values of ORs were respectively 1.3 (95% CI: 0.1 - 25.5) and 0.69 (0.0 - 37.7). Whatever the activity, the P-value was not significant and consequently, no association can be inferred regarding the activities performed by the participants (Table 1).

3.4. Prevalence of Brucella Antibodies According to Other Demographic Factors and Risk Factors Associated with Brucella Infections

The factors considered here include the sex of the participants, age, educational level, longevity in the activity and risky behaviors of the participants. No female out of 16 was found with Brucella antibodies while 26 males were reported with Brucella antibodies. This gives a seroprevalence of 10.1% in males (Table 1). Between males and females, no significant difference (P = 0.18; X2 = 1.78) was observed in the seroprevalence of Brucella antibodies. The OR of 3.8 [95% CI: 0.2 - 64.8] with a P-value of 0.35 (Table 1) indicates no significant association between sex and the presence of Brucella antibodies.

Among the 273 participants, 27 (9.9%) had less than 20 years, 73 (26.7%) were between 21 to 30 years, 65 (23.8%) between 31 to 40 years and 108 (39.6%) above 40 years (Table 1). The highest seroprevalence (12%) of Brucella antibodies was observed in participants above 40 years while the lowest seroprevalence (7.2%) was observed in those of less than 20 years (Table 1). Comparing the seroprevalence of Brucella antibodies between age groups, no significant difference (P = 0.72; X2 = 1.33) was observed (Table 1). The ORs vary from 1.0 (95% CI: 0.1 - 5.7) in participants of 31 - 40 years to 1.7 (95% CI: 0.4 - 8.1) in those above 40 years. However, no significant association was found between age groups and the risk to be in contact Brucella infections (Table 1).

Looking at the educational level, 12.8% of participants did not attend any formal education while 58.2% attended the primary education and 28.9% the secondary education. The seroprevalence of Brucella antibodies was significantly higher (P = 0.04; X2 = 6.48) in participants without any formal education (14.3%) and those with a primary education (11.9%) compared to those with secondary education (2.5%) (Table 1). The risk to be in contact with Brucella seems to significantly increase in participants with no formal education [OR = 6.4 (95% CI: 1.2 - 34.9); P = 0.03] and those with primary education [OR = 5.8; (95% CI: 1.3 - 25.3); P = 0.02].

Of the 273 participants, 64 (12.4%), 89 (32.6%) and 120 (43.9%) had respectively less than 5 years, 5 to 10 years and above 10 years of experience in their professional activities. The highest seroprevalence of Brucella antibodies of 15% was recorded in participants with more than 10 years of experience and the lowest seroprevalence of 4.7% in those with less than 5 years of experience. Comparing the seroprevalence of Brucella antibodies between groups of participants with different duration in their professional activities, significantly difference (P = 0.02; X2 = 7.48) was observed (Table 1). Performing risky activities for more than 10 years was found to be significantly associated [OR = 7.3; (95% CI: 2.0 - 25.9); P = 0.002] with the risk to be in contact with Brucella (Table 1).

One hundred and twenty-one (44.3%) participants consume raw milk. For this group of participants, the overall seroprevalence of Brucella antibodies of 16.5% was significantly higher (P = 0.004, X2 = 12.40) compared to 3.9% reported in people who did not consume raw milk (Table 1). The OR of 4.8 (95% CI: 1.9 - 12.1) with a significant P-value of 0.001 indicates that consumption of raw milk may increase the risk to be in contact with Brucella infections.

For participants with and without awareness of zoonotic diseases, the seroprevalence of Brucella antibodies were respectively 2.5% and 12.4%. Comparing the seroprevalence of Brucella antibodies between the two groups of participants, significant difference (P = 0.01; X2 = 6.32) was observed (Table 1). An OR of 0.2 (95% CI: 0.04 - 0.7) with a significant P value of 0.02 were obtained in participants having knowledge on zoonotic diseases (Table 1). Having such knowledge seems to reduce the risk of contracting Brucella infections.

In participants adopting or not the preventive measures by using protective equipment, the seroprevalence of Brucella antibodies were respectively 3.8% and 12.2% (Table 1). Between these two groups of participants, the difference in their seroprevalence was statistically significantly (P = 0.03; X2= 4.70). Moreover, for participants observing or not the hygiene measures, the seroprevalence of Brucella antibodies were respectively 7% and 21.7%. Significant difference (P = 0.001; X2 = 9.59) was observed between these two groups of participants (Table 1). For participants who observe hygiene measures and wearing protective equipment, the ORs respectively of 0.4 (95% CI: 0.2 - 1.0) and 0.2 (95% CI: 0.1 - 0.9) with significant P-values of0.03 and 0.004 indicates that observing such measures may reduce the risk of contracting Brucella infections (Table 1).

Amongst groups of participants usually assisting or not animals during parturition, the seroprevalence of 18.7% obtained in those assisting was significantly higher (P = 0.004, X2 = 12.40) compared to 1.9% recorded in other groups (Table 1). The OR of 7.2 (95% CI: 2.6 - 19.7) with a significant P-valueof0.0001 indicates that wearing protective equipment may decrease the risk to be in contact with Brucella infections (Table 1).

4. Discussion

For this study, the high number of participants enrolled at Foumban could be explained not only by the presence of the main slaughterhouse and several farms around this village, but also the largest cattle market of the West region. Compared to other villages, several animals are sold and killed at Foumban because it is the capital with the largest population of the Noun division. In such context, several inhabitants of Foumban practice activities related to livestock and their derived products. In other villages, the population is of small size and consequently, few animals are killed per week. In addition to that, the number of inhabitants practicing risky activities for human brucellosis is limited.

The overall seroprevalence of Brucella antibodies of 9.5% obtained in this study is consistent with 10.0% and 12.96% reported respectively in Uganda [38] and in the Adamawa region of Cameroon [24]. Although this seroprevalence is lower than 48.8% and 24.1% reported respectively in Nigeria [32] and Tanzania [34], it is higher than 4.7% reported in Ethiopia [33]. The observed variations could be due to the levels of exposure of each study population, the presence or absence of control program for brucellosis, the differences in the study design, the studied populations or the groups at risk that were enrolled in different studies and the participant’s behavior (eating habits and cultural practices) [24] [39]. Indeed, previous studies targeted the abattoir workers and some febrile patients [25] [32] [33] [34] while our study included more groups of people practicing activities that exposed them to Brucella infections. Known as zoonotic disease, it is important to point out that the situation of brucellosis in humans may reflect what happens in animals. In this light, our recent investigations on animal brucellosis revealed the circulation of Brucella antibodies in cattle and small ruminants of the same locality [14]. Data of the present study with those generated on animals suggest a probable transmission of Brucella between animals and humans. This hypothesis is plausible because cattle and small ruminant are recognized as the main sources for human brucellosis [6] [10] [40]. Therefore, for a better understanding of the transmission dynamics of Brucella and the current epidemiological situation of brucellosis in the affected areas, further investigations aiming to isolate and molecularly characterize Brucella strains are needed to identify Brucella species circulating in humans and animals of this locality.

The present study revealed a significant higher seroprevalence of Brucella antibodies for some socio-demographic factors like professional activities, level education and the longevity in some risky activities. These results are in agreement with previous ones [32] [34] [41]. The high seroprevalence of Brucellaantibodies in livestock keepers/herdsmen could be explained by the fact that they have several levels of expositions. For instance, they routinely consume unpasteurized milk when rearing animals. During calving and ticks picking, they are in close contact with infected animals and can easily become infected from these animals. During slaughter process, slaughterhouse workers are permanently in contact with animal discharges such as fesses, urines, fetuses. Such contacts exposed them to the risk of acquiring Brucella infections [41] [42]. Although veterinarians as well as meat and milk sellers are regularly in contact with animals and derived products, none of them were found with Brucella antibodies. This could be explained by the fact that they have been sensitized against brucellosis and other zoonotic diseases. They have therefore enough knowledge about the transmission and prevention of this disease [33]. These hypotheses are strengthened by our results of association studies reporting reduced risks for brucellosis in people having knowledge on brucellosis. The high seroprevalence reported in people practicing risky activities for more than 5 years could be explained by their permanent and longtime exposition to animals [32] [33].

Although no woman was found with Brucella antibodies, no significant difference was observed in the seroprevalence of Brucella antibodies between males and females. Our results are in agreement with those of Tsegay et al. (2017) [33]. They could be explained by the fact that the low sample size of women. In addition, the risky activities (selling milk or cooked meat) performed by women have been reported in our study to be of lower risk for brucellosis. The higher prevalence of Brucella antibodies in participants of more than 40 years could be explained by the fact that most of them have been performing the risky activities for several years. This hypothesis is in line with results of association studies reporting high risk of Brucella infections in participants practicing risky activities for long time.

Our results of bivariate analyses revealed that the consumption of unpasteurized milk and animal assistance during parturition seem to increase the risk of getting Brucella infections. These results are in agreement with those of Rubach et al. (2013) [43]. They could be explained by the fact that Brucella are mainly releasing from animal body through the milk, fetal fluids and semen. Moreover, milk and fetal fluid contain growth factors for Brucella spp [44]. As semen, milk and fetal fluids constitute the main sources for Brucella contamination, individuals who are regularly in close contact with these fluids by consuming raw milk or assisting animals during the delivery have been reported to have higher risk of contracting brucellosis [8] [45] [46]. In addition, manipulating infected materials such as carcasses, viscera, organs, blood and urine have been considered as practices enhancing the risk for the transmission of brucellosis [47]. Although the pasteurization of milk is well known to reduce the infectivity of Brucella and to limit the transmission of Brucella to humans [43], this treatment cannot be done in rural settings where equipment for pasteurization is inexistent. In such settings, boiling or heating the milk for several minutes could reduce the infectivity of Brucella [48] [49] [50].

Our results of bivariable logistic regressions analysis showed that observing personal hygiene measures and adopting safety practices such as wearing protective equipment and disinfection of premises during parturition may reduce the risk to be infected by Brucella. These results are in agreement with those of previous studies [50] [51] [52].

Although results of this study cannot be generalized to the entire population, they highlight the need of designing appropriate control measures at least for these restricted groups of people. Since the vaccination is not generally recommended for the management of human brucellosis [53] [54], the control strategies to address Brucella infections must include education and sensitization of the population, especially those for whom their daily activities are directly linked to livestock and their derivatives. For preventive measures, it will be important to avoid the consumption of raw milk or products made from raw milk. Putting together results of this study with those generated on animals of the same locality, the designing and the implementation of efficient control program for human and animal brucellosis requires the “One Health approach”. In such approach, all actors involved in livestock and human health must join their efforts for sustainable control of brucellosis. Implementing the One health concept could reduce the impact of brucellosis in order to improve human and animal health.

5. Conclusion

This study revealed Brucella antibodies in different groups of people practicing activities exposing them to brucellosis. The seroprevalence of Brucella antibodies was higher in participants with low educational level and those practicing risky activities for above 5 years. Consuming unpasteurized milk, participating to parturition and lacking knowledge on brucellosis were associated with the risk of getting human brucellosis in the Noun division of Cameroon. Results of this study suggest the need to develop and implement control measures for both human and animal brucellosis.

Acknowledgements

We wish to acknowledge all the participants of this study for their cooperation. We also thank the anonymous reviewers for helpful comments on the manuscript.

Competing Interests

The authors declare no competing interests.

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Cite this paper: Kamga, R. , Assongo, B. , Magang, E. , Fouapon, A. , Salihou, M. , Kuiate, J. and Simo, G. (2021) Seroprevalence of Brucella Antibodies and Risk Factors Associated with Human Brucellosis in High-Risk Occupational Groups of the Noun Division in the West Region of Cameroon. Journal of Biosciences and Medicines, 9, 105-123. doi: 10.4236/jbm.2021.93011.
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