Uncovering Brucella ovis in Teresina, Piauí, Brazil
Imagine a silent, invisible enemy that causes infertility in rams, triggers abortions in ewes, and devastates the livelihoods of sheep farmers across Brazil.
This isn't a work of fiction—it's the reality of Brucella ovis, a highly contagious bacterial disease that strikes at the very heart of sheep reproduction. In the microregion of Teresina, Piauí, where sheep farming represents a crucial economic activity, researchers have embarked on a mission to uncover the extent of this threat.
Through meticulous scientific investigation, they've revealed both alarming infection rates and promising diagnostic solutions. This article explores the groundbreaking study that examined 521 sheep across Teresina's microregion, revealing a 4.41% seroprevalence of this destructive pathogen and shining new light on one of sheep farming's most persistent challenges.
Sheep Tested
Municipalities
Seroprevalence
Brucella ovis is a Gram-negative coccobacillus that specifically targets sheep, particularly rams, where it causes chronic epididymitis and orchitis—painful inflammations of the reproductive organs that often lead to infertility.
In ewes, infection typically results in abortion during late pregnancy or the birth of weak lambs that struggle to survive. The economic impact extends far beyond individual animal health, causing significant losses through decreased fertility rates, reduced lambing percentages, shorter reproductive careers in valuable breeding animals, and restrictions on animal trade and movement.
The bacterium spreads primarily through venereal transmission during mating, though it can also be transmitted via contaminated bedding, equipment, or direct contact with aborted materials. What makes B. ovis particularly challenging to control is that many infected animals show no visible clinical signs while continuing to spread the bacterium. Studies have indicated that over 50% of B. ovis-infected rams display no palpable lesions in their reproductive tract, creating an invisible reservoir of infection within flocks 1 .
Sheep farming represents an important agricultural activity across Brazil, with the country maintaining approximately 17.6 million head of sheep. Mato Grosso state alone accounts for about 2% of the national flock, though sheep farming extends across multiple regions, including the Northeast where Teresina is located.
The emergence of diseases in goat and sheep flocks is common across various Brazilian regions, with ovine brucellosis being systematically studied through serological surveys over many years 2 .
To accurately assess the Brucella ovis threat in the Teresina microregion, researchers conducted an extensive field study across fourteen municipalities, collecting blood samples from 521 pubescent animals via jugular vein puncture. The study focused on sexually mature sheep as B. ovis primarily affects animals during their reproductive years.
Each sample underwent thorough analysis using two complementary serological techniques:
Blood samples were analyzed using AGID and ELISA techniques to detect Brucella ovis antibodies, providing comprehensive seroprevalence data.
The study revealed crucial data about B. ovis presence in the region:
| Diagnostic Test | Positive Samples | Percentage | Negative Samples | Percentage |
|---|---|---|---|---|
| AGID | 23/521 | 4.41% | 498/521 | 95.58% |
| Indirect ELISA | 0/521 | 0% | 497/521 | 95.39% |
| Total Suspect Cases | 24/521 | 4.61% | - | - |
Of the 521 samples analyzed using AGID, 23 (4.41%) tested positive, indicating exposure to B. ovis. The indirect ELISA identified 24 (4.61%) suspect samples but no definitively positive cases. The higher sensitivity of AGID in this study demonstrates its particular value for detecting animals that have had contact with the etiological agent in field conditions.
The research confirmed that B. ovis is present in sheep populations throughout the Teresina microregion, creating a substantive challenge for producers. These findings align with similar studies conducted in other Brazilian states, including Rio Grande do Norte (7.66%), Paraíba (5.40%), and Sergipe (3.54%), where overall seroprevalence across the three states was 5.37% based on AGID testing of 1,304 samples 3 .
The detection of B. ovis presents unique challenges that require sophisticated diagnostic approaches. The table below compares the primary methods used in the Teresina study and their relative strengths:
| Method | Principle | Advantages | Limitations | Use Case |
|---|---|---|---|---|
| AGID | Detection of antibodies through precipitation lines in agar gel | High specificity, does not require sophisticated equipment | Lower sensitivity than some other methods | Initial screening and confirmation |
| Indirect ELISA | Enzyme-linked antibody reaction measured colorimetrically | High sensitivity (97.6%), automated processing possible | May cross-react with related pathogens | Large-scale screening, research settings |
| PCR | Detection of bacterial DNA in clinical samples | Direct pathogen detection, high specificity | Requires specialized equipment and training | Confirmatory testing, ambiguous cases |
Diagnosing B. ovis infection is complicated by several factors. Due to great variation in incubation periods and intermittent shedding of the bacterium, diagnostic results can sometimes yield false negatives or false positives.
Research has identified that the types of antigens used in serological tests and the presence of correlated reproductive system diseases can interfere with immune responses, potentially affecting result accuracy 4 .
The Brazilian Ministry of Agriculture, Livestock and Supply recommends both AGID and Complement Fixation (CF) tests as official diagnostic methods. Comparative studies have shown AGID sensitivity ranging from 96.4% to 97.10%, while Complement Fixation tests demonstrated 92.7% sensitivity. Notably, ELISA tests have shown even higher sensitivity at 97.6% with 100% specificity according to some studies 5 .
The Teresina study findings fit within a broader national pattern of B. ovis distribution. A comprehensive study in Minas Gerais found that 6% of sheep flocks (3/50) were seropositive by AGID, while 4% (2/50) were positive by PCR testing of urine samples for B. ovis. Interestingly, the research also detected seropositivity in goat farms (20% - 1/5) and mixed flock farms (11.1% - 2/18), suggesting possible cross-species transmission 6 .
When using the more sensitive ELISA methodology, the Minas Gerais study detected significantly higher rates of positivity—19.5% (8/41) of sheep properties and 61.1% (11/18) of properties with mixed flocks showed evidence of B. ovis exposure.
Epidemiological research has identified several factors that increase the likelihood of B. ovis infection in sheep flocks:
| Risk Factor | Impact Level | Protective Measure | Effectiveness |
|---|---|---|---|
| Lack of worker training | High (OR = 3.68) | Regular training on biosecurity | Significantly reduces risk |
| Mixed-species flocks | Moderate to High | Species separation | Reduces cross-transmission |
| Purchase of untested animals | High | Pre-purchase testing | Prevents introduction |
| Mature animals | Higher than young | Separate management by age | Limits spread to young stock |
| Natural breeding without health checks | High | Breeding soundness exams | Identifies infected rams |
Research from Northeast Brazil has identified that the lack of trained workers (odds ratio = 3.68; 95% CI = 1.08-12.60; p=0.038) represents a significant risk factor for B. ovis occurrence in flocks 7 . Additionally, studies have confirmed that matrices (7.54% - 52/690) are significantly more affected than young animals (2.19% - 10/457), highlighting the cumulative risk of infection over time.
The identification of Brucella ovis in sheep from the Teresina microregion, with a seroprevalence of 4.41%, confirms the widespread distribution of this pathogen in Piauí state and underscores its significance as a cause of reproductive failure in sheep flocks. These findings, consistent with studies from other Brazilian states, highlight the substantial threat that ovine brucellosis represents to sheep production systems across the country.
Moving forward, a multifaceted approach combining regular testing using sensitive and specific diagnostic methods, strict biosecurity measures, targeted worker education, and careful flock management represents the most effective strategy for controlling B. ovis. The higher sensitivity of AGID in detecting infected animals in the Teresina study suggests it remains a valuable tool for screening programs in similar epidemiological contexts.
For the Teresina microregion and similar sheep-producing areas, the development and implementation of control and eradication programs by official agencies should be considered a priority. Simultaneously, the implementation of sanitary measures and increased awareness among sheep producers will be essential to mitigate the economic impacts of this disease and protect the sustainability and productivity of sheep farming in Brazil.