Economic impact and epidemiological aspects of subclinical mastitis and caprine arthritis-encephalitis in the semiarid northeastern region of Brazil

Dairy activity in the semi-arid region has gained prominence due to its profit potential; however, there are still sanitary problems that result in significant economic impact. Thus, this study aimed to assess the economic impact and to conduct an epidemiological study of caprine arthritis-encephalitis (CAE) and subclinical mastitis in dairy goat herds of the semi-arid northeastern region of Brazil. The study proceeded with the collection of blood (n = 351) and milk samples (n = 321) from 15 rural properties with up to 50 animals, risk factor assessment, economic profile analysis, and georeferencing of the properties. The blood serum obtained was subjected to the AGID test. The milk samples were cultured on blood agar, and the reading was performed 24 hours after incubation. Overall, 3.4% of the animals were seropositive for CAE, and 15.8% were diagnosed with subclinical mastitis. 71.95% of the positive animals belonged to properties with a semi-intensive rearing system, weekly cleaning of the facilities, and no pre- or post-dipping. Subclinical mastitis caused by the main agent Staphylococcus spp. was associated with the breed type of the animals, highlighting two risk factors: purebred animals (OR = 12.52) and the milking performed close the soil (OR = 18.07). A reduction of up to 35.34% was observed in the income of dairy properties, constituting a considerable economic impact. Due to these sanitary problems, the economic impact demonstrates the need for a sanitary management program focused on these infirmities.


INTRODUCTION
The states of Bahia and Pernambuco are the largest goat producers in Brazil, totaling 9 million heads (IBGE, 2017). However, poor handling conditions and zootechnical structures have a significant influence on the occurrence of health problems (GUILHERME et al., 2017).
Caprine Arthritis-Encephalitis (CAE) and mastitis are among the main sanitary problems affecting dairy goat herds. CAE is a multisystemic, infectious disease with a long incubation period and a chronic progressive course, showing significant economic importance. The main clinical signs of CAE are arthritis characterized by enlarged carpus, leading to locomotion problems in animals, severe mastitis with mammary gland nodules, and purulent pneumonia (PENIDO et al., 2017).
Mastitis, another relevant illness, is characterized by a multifactorial infection responsible for significant losses due to its control and treatment expenses. This disease affects dairy goat and sheep herds as an inflammation of the mammary gland, with the intensity of the disease being determined by the nature and virulence factors of bacteria or groups of bacteria, the resistance of the agent to antibiotics, and other host-related factors (GABLI et al., 2019). The most common pathogens related to intramammary infections in small ruminants that can cause clinical and subclinical mastitis are those of the genus Staphylococcus (OLECHNOWICZ; JAŚKOWSKI, 2014).
Studies associating mastitis with economic damage are mostly directed towards bovines. The economic impact caused by mastitis varies widely across properties, being directly associated with the importance given to disease control and prevention (HOGEVEEN; VAN DER VOORT, 2017;RUSHTON, 2017;VISSIO et al., 2015). The treatment with different antimicrobials implies high costs, especially at the beginning of treatment, being economically disadvantageous (STEENEVELD et al., 2011).
Aiming to support the creation of sanitary management programs in dairy properties, it is essential to investigate the impact and real epidemiological situation of CAE and the cases of mastitis in this region. Thus, this study aimed to determine the economic impact and the epidemiological aspects of CAE and mastitis in dairy goat herds in the semi-arid northeastern region of Brazil.

MATERIAL AND METHODS
The study began after the approval by the Ethics Committee on Animal and Human Experimentation (CEUA) of the Federal University of São Francisco Valley (UNIVASF), under the number 0002/130318. The study covered six municipalities located in the states of Pernambuco and Bahia (Petrolina, Lagoa Grande, and Santa Maria da Boa Vista-PE, in addition to Juazeiro and Curaçá, in Bahia). A non-probabilistic convenience sampling was adopted for properties with herds containing up to 50 animals, totaling 18 properties.
Blood was collected from 351 goats, most of which females, including breeders. Milk was collected from 321 dairy goats. All animals were over one year of age, and the predominant breeds were Brown Alpine, Brown Swiss, Saanen, Anglo Nubian, Toggenburg, and crossbreed animals. To search for anti-CAE antibodies, the samples were subjected to the Agar Gel Immunodiffusion test (AGID) using a kit from Biovetech ® -Indústria e Comércio de Produtos Biotecnológicas Ltda. For milk culture, 10μl aliquots were taken from each milk sample using a calibrated loop and spread onto the quadrants of a blood agar plate plus 5% sheep blood. The isolated colonies were observed regarding their morphology, size, pigmentation, and the presence of hemolysis. The isolated microorganisms were observed under a microscope using smears stained by the Gram method. The catalase and coagulase tests were used for genus confirmation.
To study the risk factors associated with infection, a crosssectional study was conducted using a questionnaire with questions regarding the breeder, the general characteristics of the property, such as species, breed (pure or mixed breed), management system (intensive, semi-intensive, or extensive), and sanitary aspects (frequency of cleaning of the facilities, milking place, pre-and post-dipping), in addition to issues related to technical assistance to the producer. The analysis of risk factors was performed in two stages, comprising univariate and multivariate analysis. In the first moment (univariate analysis), the variables associated with the presence of mastitis were studied. Each independent variable was crossed with the dependent variable (mammary gland infection), with each animal considered a sample unit. For the study of the variables associated with a CAE focus, the rural property was considered a sample unit, with the CAE focus as the dependent variable. The variables with a value of p <0.2 using the chi-square test or Fisher's exact test (ZAR, 1999) were selected and used in the multivariate analysis, using the multiple logistic regression according to HOSMER & LEMESHOW (2000). The collinearity between the predictor variables was verified by correlation analysis; for the variables that showed strong collinearity (correlation coefficient ≥ 0.9), one of the two was excluded from the multiple analysis according to the biological plausibility (DOHOO et al., 1996). The significance level adopted in the multiple analysis was 5% using the SPSS 13.0 software for Windows.
The presence of CAE foci was correlated with the number of mastitis cases by Spearman's test, which assesses the correlation between two quantitative variables (ARNDT, 1999).
Regression analysis was employed for the economic assessment by considering the presence/absence of mastitis and the average milk production (L/day) per property. Furthermore, the simultaneous presence of mastitis and CAE foci was also considered, evaluating their impact on reducing the milk volume produced by the herd and the revenue from milk commercialization by the producer.

RESULTS AND DISCUSSION
The search for antibodies against the CAE virus revealed that 3.4% (12/351) of the animals were seropositive. The presence of subclinical mastitis was observed in 15.8% (51/321) of the properties using a milk culture technique in which the Staphylococcus spp. and Micrococcus spp. bacteria were obtained from goat milk samples (Table 1). Subclinical mastitis occurs predominantly in small ruminant herds, with a prevalence between 5% and 30%, reaching high rates in certain management situations (CONTRERAS et al., 2007). The presence of subclinical mastitis varies widely among herds, compromising the income of the small rural producer. Poor hygiene, inadequate handling, and the non-separation of infected animals contribute to spreading mastitis in goat herds (ZHAO et al., 2015). The absence of mastitis cases in three herds is justified by the climatic conditions, which can act as a barrier to the disease since dry and sunny environments act by reducing the cases of subclinical mastitis in lactating goats (MEGERSA et al., 2010).
The agent identified in the study belongs to the genus Staphylococcus, one of the main causes of subclinical mastitis in goats, and promotes an increase in the somatic cell count (CCS), leading to decreased milk production (SALABERRY et al., 2016).
In the case of positive properties for subclinical mastitis, the presence of Staphylococcus spp. Bacteria, found in most samples, suggests contamination due to poor hygiene of the handler as well as environmental contamination by Micrococcus spp. These results come from uncontrolled properties regarding environmental hygiene, with simple facilities and less frequent or no pre-and post-dipping. Some goat breeding properties with cases of subclinical mastitis in the state of Bahia showed a greater predominance of Staphylococcus spp. in the milk samples, isolated in 91.7% of the samples (CAVALCANTE et al., 2013). A low frequency of seropositive animals was observed for CAE and also for mastitis. Most of the owners who participated in this study belonged to a local association, all of whom are considered small farmers. Those who had purchased animals of lower zootechnical potential dismissed the main ones, especially at the time of milking, with poor hygienic-sanitary facilities and conditions. Otherwise, those with a more homogeneous herd usually performed milking on a platform and used teat antisepsis techniques, justifying the lower percentage of positive animals under these circumstances. Figure 1 exhibits the spatial distribution of the properties with positive animals for the studied infirmities.
The negative status for CAE in most herds was possibly due to the acquisition of animals from properties in Bahia and Pernambuco, which have a low prevalence of the disease.
Another hypothesis is the low viral, which becomes an obstacle for diagnosis by the AGID test (ANDRÉS et al., 2013). The genetic factors of the host can also influence the efficiency of the immune response, controlling the viral load of these lentiviruses (CARDINAUX et al., 2013).
In this study, there was no correlation between CAE foci and the presence of mastitis, despite the significant reduction in milk production. This result corroborates a study that investigated changes in milk and blood cells of dairy goats with natural CAEV infection, verifying no dysfunction of these cells as well as no greater susceptibility of the goat herd to secondary diseases (SANTOS et al., 2012).
The socio-economic assessment showed that 70% of breeders belong to local associations or cooperatives and have already received some goat farming training. Regarding the characteristics of the properties, 80% had a weekly cleaning frequency. The health management variable showed a mortality rate below 10% in properties with a semi-intensive farming system. Of the properties visited, 60% are formed by goats from neighboring properties located in the same state, most of which quarantine and vaccinate animals before introducing them into the herd, although without performing examinations.
One of the main factors for the presence of the infection was the cleaning frequency of the facilities. Cleaning was carried out weekly in 80.68% of the properties. The pre-and postdipping preventive technique was not performed at the time of milking, resulting in a percentage of 80.04% of positive animals for mastitis. On the other hand, the properties that performed quarantine showed a lower percentage of positive animals than those who did not employ the same procedure or due to diseases (67.76%). The sanitary practices of preventive disease management contribute positively to reduce the number of pathogens in the livestock, especially those directed towards the proper hygiene of the environment and pre-and post-milking antisepsis.
In the univariate analysis, an association was observed between the presence of the disease and the lack of technical assistance, with a higher percentage of positive animals in the properties that were not assisted by a veterinarian (86.04%). The absence of qualified technical assistance is a relevant factor for maintaining the health status of the herds. Thus, once breeders do not receive proper technical instruction, the number of sanitary problems increases (Table 2).
This study showed that no variable constituted a risk factor for CAE. In the multivariate analysis, the breed type and milking place variables were risk factors for mastitis (Table 3). Regarding the breed, this result occurs because purebred animals show greater milk production, being more susceptible to mastitis. Regarding the milking place, the milking performed close to the soil increases the number of animals with mastitis. The microorganisms present in the soil constitute an important cause of the disease, being mainly responsible for environmental mastitis, which is caused by relevant pathogens such as bacteria of the family Enterobacteriaceae.  Regarding the breed type, the goats considered purebred and, therefore, with a higher dairy potential were more likely to develop the disease (OR = 12.52). Goats that show high milk yields are less resistant to intramammary infections, especially in times of climatic variation (AKTER et al., 2020).
The economic analysis showed that milk production was lower in herds with mastitis (R2 = 0.7315; p <0.0178). On the other hand, in the analysis in which milk production was observed under the simultaneous presence of both diseases, there was no statistically significant difference despite the drop in milk production (Table 4).
In this study, mastitis brought economic losses equivalent to 35.34% in the income of small rural producers. These losses are due to the reduction in milk production, costs with treatment, and dismissal of animals. The high economic impact demonstrates the need to raise awareness among breeders regarding the economic relevance of the disease, requiring the involvement of the several participants of the goat milk production chain in order to mitigate the effects of the disease. This study also revealed that there was no sign of CAE in the animals of the visited properties, and most breeders are unaware of the signs of Caprine Arthritis Encephalitis and its impact on the herd. These findings corroborate a study that reports the lack of data on the presence and absence of clinical signs in small ruminant herds of the region, influencing this unawareness (MICHIELS et al., 2018).

CONCLUSIONS
The study results demonstrate the circulation pathogens of relevance to the production chain of dairy goats in the targeted region. The economic impact due to these agents demonstrates the need to establish a sanitary management program focused on these infirmities, requiring support from public institutions to raise awareness among breeders regarding the importance of prophylactic practices in the sanitary management of the herds.

ACKNOWLEDGMENTS
To the Science and Technology Support Foundation of the State of Pernambuco, for the financial support.