The first report in new zealand of Lymnaea columella say (Mollusca: gastropoda) an intermediate host of the liver fluke Fasciola hepatica L

Six herds of dairy cattle, in which infection had persisted after measures had been employed to eradicate brucellosis, were investigated in detail. One hundred and two animals out of 700 (14.6%) had evidence of the disease from cultural or serological tests. Only 4 infected animals aborted; the remaining 98 animals with brucellosis exhibited no clinical sign of the disease, and 52 were heifers calving for the first time. Sixty-five of the 700 animals (9.3%) produced brucella-infected vaginal discharges at the end of a normal period of gestation, and another 17 (2.4%) were detected only by the brucellosis (Brewer) card test (BCT) or complement fixation test (CFT). All the infected animals were removed from the herds immediately after detection.

About 2 weeks after all the cows had calved, 20 of the remain-ing 510 animals (3.9%) in 4 of the herds became positive to one or more tests and 8 excreted brucellae in their milk. The pregnancy of three 2-year-old primiparous heifers terminated normally and one aborted. All four discharged brucellae until they were slaughtered 20 to 35 days after parturition.

Twenty-five of the 102 infected animals were detected by bacteriological, and 29 by serological, means only. A compari-son was made of the results of the testsfrom 73 culturally positive animals; 4.1% of the sera were CFT positive but BCT negative, and 5.5% were BCT positive but CFT negative. An attempt has been made to explain the large numbers (34.2%) of infected animals that were serologically negative.     

Experimental infection of rabbits (Oryctolagus cuniculus) with Brucella suis biovar 1 isolated from wild hares (Lepus europaeus)

Brucella suis biovar 1 is the causative agent of brucellosis in several domestic and wild animals and it is a common agent of human brucellosis. European hares (Lepus europaeus) have been shown to be infected by B. suis biovar 1 and the transmission to other animals has been suggested. In this work, experimental rabbits (Cuniculus orictolagus) were infected with B. suis biovar 1 isolated from wild hares. Infected rabbits showed high serological response in 2 weeks after discharge and typical granulomatous lesions (2mm diameter) were found in liver, spleen and kidneys after 50 days. B. suis biovar 1 was cultured from the lesion of the organs mentioned above as well as from urine, placenta and fetuses. These data suggest that hares are a potential source for horizontal transmission of B. suis biovar 1 to other mammalians.     

Transmission of Brucella canis by contact exposure

Transmission studies demonstrated that canine brucellosis can spread from infected to susceptible males maintained in close contact after 4 to 6 months of cohabitation. Spread by males occurred after epididymitis was observed in the infected dogs. Transmission via contaminated urine was suspected, but not proved. The bladder urine of infected males, probably contaminated with seminal fluid, contained higher numbers of B. canis organisms than did that of female dogs. Highest concentrations of bacteria in urine were found between postinfection weeks 8 and 12. Infected females transmitted the infection to contact females after 5 months. Immature females or males infected with B. canis did not transmit brucellosis until after an estrus or a mating was observed--about post-contact months 10-12.     

The use of skin delayed-type hypersensitivity as an adjunct test to diagnose brucellosis in cattle: a review

Brucellosis, caused by bacteria of the genus Brucella, is a contagious disease that causes economic loss to owners of domestic animals due to loss of progeny and milk yield. Because cattle, sheep, goats, and to a lesser extent pigs are considered to be the source of human brucellosis, serological tests have been used to screen domestic animals for antibodies against Brucella. Although the serological tests helped to eradicate brucellosis in many countries, serological tests are not always adequate to detect latent carriers of Brucella. Therefore, the use of the skin delayed-type hypersensitivity (SDTH) test, which is independent of circulating antibodies, might improve the diagnosis of brucellosis. In the literature, however, there are conflicting reports as to the value of the SDTH test for the diagnosis of brucellosis. Some studies consider the test unreliable, whereas others advocate its use because it detects brucellosis earlier than serological tests. The objectives of this study were therefore to assess the characteristics of the SDTH test, to select a Brucella strain that will yield a suitable brucellin for use in the field, and to determine whether the use of serological tests in combination with the SDTH test improves the detection of brucellosis. The results of this study clearly show that the SDTH test detects latent carriers of Brucella and confirms brucellosis in cattle with ambiguous serological test results. Brucellins prepared from smooth or mucoid strains of Brucella are better suited for use in the field than brucellins prepared from rough strains because they detect brucellosis in cattle with acute as well as chronic infection. The SDTH test is highly specific (99.3% specificity), and repeated testing of naive cattle or cattle infected with microorganisms that serologically cross-react with Brucella does not sensitize cattle to subsequent SDTH tests. However, it is possible that some naive cattle may serologically react to the injection of brucellin. The effect of these serological reactions on the sero-diagnosis of brucellosis is limited, because cattle may only now and then react serologically either with the serum agglutination test (SAT) or the complement fixation test (CFT). Nevertheless, cattle infected with microorganisms that serologically cross-react with Brucella may test seropositive for brucellosis 4 to 7 weeks after injection of brucellin, depending on the cross-reacting microorganism. The value of the SDTH test for the diagnosis of brucellosis was demonstrated after an outbreak of brucellosis. When the SDTH test was used in combination with SAT and CFT at diagnostic threshold > or =2 mm or > or =1 mm (increase in skinfold thickness), respectively, 39/44 (88%) or 42/44 (95%) of the infected cattle were detected compared with only 27/44 (61%) when SAT and CFT were used. When cattle in areas of low prevalence or in areas free from brucellosis are tested with the SDTH test an increase > or =2 mm in skinfold thickness should be considered indicative of infection. When the control and eradication of brucellosis is based on test-and-slaughter, an increase of > or =1 mm in skinfold thickness should be considered indicative of infection. Repeated serological testing complemented with the SDTH test in this programme will shorten the quarantine (movement control) period of a suspect herd, limiting the financial loss incurred during outbreaks of the disease. Consequently, since the SDTH test usually does not interfere with the serological diagnosis and can safely be used to establish the infection status of cattle in a suspect herd, it is opportune to consider adding the SDTH test to the procedure currently used to diagnose brucellosis in individual animals.     

Evaluation of a delayed-type hypersensitivity test for the diagnosis of Brucella abortus infection in cattle

The delayed-type hypersensitivity (DTH) test was used to diagnose brucellosis in two cows experimentally induced with brucellosis, and 176 dairy cows from a farm suspected of brucellosis. DTH test results were compared with results of the milk ring test, the serum agglutination test, the complement fixation test and the Coombs test. Cows positive in the DTH test and in one of the other tests were examined bacteriologically. In experimentally infected animals the DTH test was positive 10 days after infection, 1-4 weeks before serologic tests indicated brucellosis. Although the DTH test was positive during the whole experiment, on the one occasion when serologic titres were high, it was negative. Of the 176 dairy cows, 45 were positive in one or more serologic tests. In twelve cows (29%) the diagnosis was inconclusive because they were positive in only one of the serologic tests. In these cases the DTH test confirmed the infection. Three cows with high serologic response tested negative in the DTH test. B. abortus was isolated from 13 of 15 cows examined. We conclude that when serologic results are ambiguous, the DTH test is a useful additional technique for diagnosing brucellosis.     

Detection of brucellosis in diary herds after an outbreak of the disease using a delayed-type hypersensitivity test

A study of 14 herds was conducted to assess the skin delayed-type hypersensitivity (SDTH) test used in combination with the serum agglutination test and complement fixation test to curtail the spread of brucellosis. The tests were used to screen dairy herds suspected of brucellosis, and herds located near infected herds. The herds were tested every 5–6 weeks for 6 months. Cattle with a palpable skin swelling at the injection site of the allergen were considered as brucellosis suspects and were slaughtered. Supramammary lymph nodes of these cattle were collected and examined bacteriologically to determine their infection status.

Brucellosis was detected and confirmed bacteriologically in three seronegative herds in which cattle tested positive with the SDTH test. Brucellosis was also confirmed bacteriologically in five seropositive herds in which cattle tested positive with the SDTH test. Brucellosis was not confirmed bacteriologically in one seronegative and four seropositive herds in which cattle reacted positively with the SDTH test. One herd reacted negatively in all tests. Because the SDTH test is able to detect latent carriers of Brucella organisms in seronegative herds, we recommend that the SDTH test be used in combination with serologic tests to curtail the spread of brucellosis.     

Epidemiology and control of brucellosis in China

The paper describes the history and evolvement of brucellosis in China. It presents the variation of epidemic situation, epidemiological characteristics, application of vaccines and control in brief. Before 1980s, human and animal brucellosis was quite severe; during 1980s, the incidence of human and animal brucellosis was relatively low, and seemed to decrease during the decade. During 1990s, there were no obvious changes in the incidence of animal brucellosis, but the incidence of human brucellosis increased, especially from 1995 to 2001. There are not only some common characteristics but also some differences in brucellosis epidemiology relative to that reported in the rest of the world. For the entire country, B. melitensis was the predominant strain associated with outbreaks, and the epidemic peak is from February to June. Several Brucella vaccines have been used in China for prevention and control of brucellosis. such as B. abortus 104 M in humans, B. suis S2 in animals. The introduction of comprehensive measures has allowed great progress in the prevention and control of brucellosis in China. Surveillance points were set-up countrywide to estimate the epidemic situation. In addition, we discussed the new characteristics of brucellosis in China, the influence of the El Nino phenomenon on brucellosis epidemic situation, the phenomenon of antigenic interference between Brucella species and some disadvantages of live Brucella vaccines.     

绥德县1996年-2008年布鲁菌病监测分析

通过对绥德县1996年-2008年畜间布鲁菌病血检情况的分析,得出绥德县从1996年暴发人畜间布病后,经过12年的艰苦防治,取得了一定成绩,畜间布鲁菌病阳性率明显下降.并结合人间布鲁菌病发病情况,提出今后布鲁菌病综合防控的建议.     

Brucellosis due to Brucella suis in a swine herd associated with a human clinical case in the State of S?o Paulo, Brazil

Brucella suis has been recognized as the major etiological agent of human brucellosis in areas free from Brucella melitensis infection. However, with changes in swine management, the occurrence of swine brucellosis has decreased as has the human incidence of B. suis infection. A swine brucellosis outbreak within a herd from Jaboticabal (S?o Paulo, Brazil) was detected in July 2006. The herd comprised approximately 300 sows and 1,500 finishing animals. Many sows within this herd experienced abortions, while others exhibited vaginal discharge; three sows suffered posterior paralysis. Among 271 sows, 254 (93.7%) tested positive for brucellosis by complement fixation, and among 62 randomly bled finishing animals, 17 (27.4%) also tested positive. The B. suis biovar 1 was cultured from 14 aborted fetuses and six sows. Brucella was identified using routine methods. Fourteen farm workers were tested using agglutination tests, with three workers showing evidence of Brucella antibody titers. A 39-year-old woman, who worked with maternal pigs and had direct contact with aborted fetuses, presented an agglutinating titer of 480?IU/mL and displayed clinical signs of infection. Our findings suggest that despite a reduction of swine brucellosis throughout Brazil, B. suis infection still occurs, thereby posing a zoonotic risk.     

Brucellosis: A re-emerging zoonosis

Brucellosis, especially caused by Brucella melitensis, remains one of the most common zoonotic diseases worldwide with more than 500,000 human cases reported annually. The bacterial pathogen is classified by the CDC as a category (B) pathogen that has potential for development as a bio-weapon. Brucella spp. are considered as the most common laboratory-acquired pathogens. The geographical distribution of brucellosis is constantly changing with new foci emerging or re-emerging. The disease occurs worldwide in both animals and humans, except in those countries where bovine brucellosis has been eradicated. The worldwide economic losses due to brucellosis are extensive not only in animal production but also in human health. Although a number of successful vaccines are being used for immunization of animals, no satisfactory vaccine against human brucellosis is available. When the incidence of brucellosis is controlled in the animal reservoirs, there is a corresponding and significant decline in the incidence in humans.     

Human Brucellosis Trends: Re‐emergence and Prospects for Control Using a One Health Approach in Azerbaijan (1983–2009)

Brucellosis is one of the most common and widely spread zoonotic diseases in the world. Control of the disease in humans is dependent upon limiting the infection in animals through surveillance and vaccination. Given the dramatic economic and political changes that have taken place in the former Soviet Union, which have limited control, evaluating the status of human brucellosis in former Soviet states is crucial. We assessed annual spatial and temporal trends in the epidemiology of human brucellosis in Azerbaijan, 1983–2009, in conjunction with data from a livestock surveillance and control programme (2002–2009). To analyse trends, we used a combination of segmented regression and spatial analysis. From 1983 to 2009, a total of 11 233 cases of human brucellosis were reported. Up to the mid‐1990s, the incidence of human brucellosis showed a pattern of re‐emergence, increasing by 25% annually, on average. Following Soviet governance, the incidence rates peaked, increasing by 1.8% annually, on average, and subsequently decreasing by 5% annually, on average, during the period 2002–2009. Despite recent national declines in human incidence, we identified geographic changes in the case distribution characterized by a geographic expansion and an increasing incidence among districts clustered in the south‐east, compared to a decrease of elsewhere in the country. Males were consistently, disproportionately afflicted (71%) and incidence was highest in the 15 to 19 age group (18.1 cases/100 000). During the period 2002–2009, >10 million small ruminants were vaccinated with Rev1. Our findings highlight the improving prospects for human brucellosis control following livestock vaccination; however, the disease appears to be re‐emerging in south‐eastern Azerbaijan. Sustained one health measures are needed to address changing patterns of brucellosis in Azerbaijan and elsewhere in the former Soviet Union.     

The use of skin delayed‐type hypersensitivity as an adjunct test to diagnose brucellosis in cattle: A review

Summary

Brucellosis, caused by bacteria of the genus Brucella, is a contagious disease that causes economic loss to owners of domestic animals due to loss of progeny and milk yield. Because cattle, sheep, goats, and to a lesser extent pigs are considered to be the source of human brucellosis, serological tests have been used to screen domestic animals for antibodies against Brucella. Although the serological tests helped to eradicate brucellosis in many countries, serological tests are not always adequate to detect latent carriers of Brucella. Therefore, the use of the skin delayed‐type hypersensitivity (SDTH) test, which is independent of circulating antibodies, might improve the diagnosis of brucellosis. In the literature, however, there are conflicting reports as to the value of the SDTH test for the diagnosis of brucellosis. Some studies consider the test unreliable, whereas others advocate its use because it detects brucellosis earlier than serological tests. The objectives of this study were therefore to assess the characteristics of the SDTH test, to select a Brucella strain that will yield a suitable brucellin for use in the field, and to determine whether the use of serological tests in combination with the SDTH test improves the detection of brucellosis. The results of this study clearly show that the SDTH test detects latent carriers of Brucella and confirms brucellosis in cattle with ambiguous serological test results. Brucellins prepared from smooth or mucoid strains of Brucella are better suited for use in the field than brucellins prepared from rough strains because they detect brucellosis in cattle with acute as well as chronic infection. The SDTH test is highly specific (99.3% specificity), and repeated testing of naive cattle or cattle infected with microorganisms that serologically cross‐react with Brucella does not sensitize cattle to subsequent SDTH tests. However, it is possible that some naive cattle may serologically react to the injection of brucellin. The effect of these serological reactions on the sero‐diagnosis of brucellosis is limited, because cattle may only now and then react serologically either with the serum agglutination test (SAT) or the complement fixation test (CFT). Nevertheless, cattle infected with microorganisms that serologically cross‐react with Brucella may test seropositive for brucellosis 4 to 7 weeks after injection of brucellin, depending on the cross‐reacting microorganism. The value of the SDTH test for the diagnosis of brucellosis was demonstrated after an outbreak of brucellosis. When the SDTH test was used in combination with SAT and CFT at diagnostic threshold ≥2 mm or ≥1 mm (increase in skinfold thickness), respectively, 39/44 (88%) or 42/44 (95%) of the infected cattle were detected compared with only 27/44 (61%) when SAT and CFT were used. When cattle in areas of low prevalence or in areas free from brucellosis are tested with the SDTH test an increase ≥2 mm in skinfold thickness should be considered indicative of infection. When the control and eradication of brucellosis is based on test‐and‐slaughter, an increase of ≥1 mm in skinfold thickness should be considered indicative of infection. Repeated serological testing complemented with the SDTH test in this programme will shorten the quarantine (movement control) period of a suspect herd, limiting the financial loss incurred during outbreaks of the disease. Consequently, since the SDTH test usually does not interfere with the serological diagnosis and can safely be used to establish the infection status of cattle in a suspect herd, it is opportune to consider adding the SDTH test to the procedure currently used to diagnose brucellosis in individual animals.     

Recovery of microorganisms from synovial and pleural fluids of animals using hyperosmolar media

L-phase (CWD) broth and plate media were used in parallel with conventional microbiological media during a 3-year period for culturing synovial and pleural fluids of animals. Two kinds of recoveries were obtained where parallel conventional methods were negative: (1) parent or normal bacteria, in very low numbers; and (2) Type B CWD variants in equally low numbers. Organisms in group 1 were: Streptococcus zooepidemicus from horses (2X); β-hemolytic streptococci, Lancefield Gp. G (2X); Staphylococcus aureus; Actinobacillus, and Actinomyces viscosus. Group 2 consisted of Bacteroides sp., Propionibacterium acnes, and three “Nocardia-like” sp. Catalase + Actinomyces was not recovered equally well on CWD plates as on conventional media with fluids obtained during ampicillin treatment. This occurred in spite of the fact that the CWD media was shown to support growth and reversion of laboratory induced L-phase variants of Nocardia caviae and N. asteroides, and had facilitated recovery of a Bacteroides L-phase variant from a pleural fluid. The nature of this fault in the media is under investigation in this laboratory.     

Simple and rapid field tests for brucellosis in livestock

Four simple and rapid field tests for the serodiagnosis of brucellosis in cattle, goat, sheep and swine were developed. The performance of the assays was investigated using serum samples collected in Portugal from animals originating from herds with a defined sanitary status with respect to the presence of brucellosis. The sensitivity calculated for the bovine, caprine, ovine and swine Brucella lateral flow assays based on results obtained for samples collected from animals with culture confirmed brucellosis was 90%, 100%, 90% and 73%, respectively. None of the samples from animals from herds free of brucellosis reacted in the flow assays indicating a high specificity. However, as expected, some degree of reactivity was observed when testing selected serum samples that reacted non-specific in reference tests for brucellosis.     

Pathologic changes associated with brucellosis experimentally induced by aerosol exposure in rhesus macaques (Macaca mulatta)

OBJECTIVE: To develop an aerosol exposure method for induction of brucellosis in rhesus macaques (Macaca mulatta). ANIMALS: 10 adult rhesus macaques. PROCEDURE: 8 rhesus macaques were challenge exposed with 10(2) to 10(5) colony-forming units of Brucella melitensis 16M by use of an aerosol-exposure technique, and 2 served as control animals. All macaques were euthanatized 63 days after challenge exposure. Gross and microscopic lesions, bacterial burden in target organs, and histologic changes in tissues were evaluated. RESULTS: Grossly, spleen weights were increased in exposed macaques, compared with spleen weights in control macaques. Histologically, there was inflammation in the liver, kidneys, spleen, testes, and epididymides in exposed macaques. The spleen and lymph nodes had increased numbers of lymphohistiocytic cells. Morphometrically, the spleen also had an increased ratio of white pulp to red pulp. Areas of hepatitis and amount of splenic white pulp increased with increasing exposure dose. CONCLUSIONS AND CLINICAL RELEVANCE: Pathologic findings in rhesus macaques after aerosol exposure to B melitensis are similar to those observed in humans with brucellosis. IMPACT FOR HUMAN MEDICINE: These results may aid in the development of a vaccine against brucellosis that can be used in humans.     

Evaluation of immunochromatographic assay for serodiagnosis of Brucella canis

Canine brucellosis is a contagious disease with venereal and oral modes of transmission that produces late abortion in females, epididymides and prostates in males. Diagnosis is difficult because of unstable serum antibody titers that vary from individual to individual as well as between different methods used for their detection. The objective of this work was to evaluate the clinical utility of the immunochromatographic assay (ICA) for serodiagnosis of dogs suspected of having brucellosis, and results were compared with those obtained for hemoculture (HC) and the rapid screening agglutination with 2-mercaptoethanol (2-ME RSAT). The all experimentally infected dogs were positive in ICA, HC and 2-ME RSAT from 5 weeks, 7 weeks, and 3 weeks after infection, respectively. Also, among dogs selected from 10 different breed kennels occurred brucellosis, 24.8%, 39.5% and 39.1% of dogs tested were detected as positive with HC, 2-ME RSAT and ICA, respectively. The kappa value between 2-ME RSAT and ICA was 0.89. The results of this study showed that sensitivity and specificity of the ICA are comparable with those obtained using conventional serological and bacteriological test for brucellosis. In conclusion, the ICA kit provides a handy and accurate tool for the rapid serodiagnosis of canine brucellosis.     

Brucellae through the food chain: the role of sheep, goats and springbok (Antidorcus marsupialis) as sources of human infections in Namibia

A confirmed case of human brucellosis motivated an investigation into the potential source of infection in Namibia. Since domestic animals are principal sources of Brucella infection in humans, 1692 serum samples were screened from sheep, goats and cattle from 4 presumably at-risk farms and 900 springbok (Antidorcas marsupialis) serum samples from 29 mixed farming units for Brucella antibodies by the Rose-Bengal test (RBT) and positive cases confirmed by complement fixation test (CFT). To assess the prevalence of human brucellosis, 137 abattoir employees were tested for Brucella antibodies using the standard tube agglutination test (STAT) and by enzyme linked immunosorbent assay (ELISA). Cattle and sheep from all 4 farms were negative by RBT and CFT but 2 of the 4 farms (Ba and C) had 26/42 and 12/285 seropositive goats, respectively. Post mortem examination of seropositive goats revealed no gross pathological lesions typical of brucellosis except enlarged mesenteric and iliac lymph nodes seen in a single buck. Culture for brucellae from organs of seropositive animals was negative. None of the wildlife sera tested positive by either RBT or CFT. Interviews revealed that besides the case that prompted the investigation, a family and another person from other farms with confirmed brucellosis shared a common history of consumption of unpasteurised goat milk, home-made goat cheese and coffee with raw milk and prior contact with goats, suggesting goats as the likely source of infection. All 137 abattoir employees tested negative by STAT, but 3 were positive by ELISA. The 3 abattoir workers were clinically normal and lacked historical connections with clinical cases. Although goats are often associated with B. melitensis, these studies could not explicitly implicate this species owing to cross-reactivity with B. abortus, which can also infect goats. Nevertheless, these data reinforce the need for a better National Control Programme for brucellosis in Namibia.     

The "effects" of Rev-1 vaccination of sheep and goats on human brucellosis in Greece

Vaccination of young animals (3-6-month-old sheep and goats) with Rev-1 vaccine for 15 years in Greece, importantly decreased the abortions in sheep and goats as well as the incidence of brucellosis in humans. After the stop of vaccination in 1994, all over Greece, the prevalence of brucellosis in animals and the incidence in humans quickly increased. It was a positive rank correlation (0.90) among these variables. Once an emergency mass-vaccination programme of young and adult animals with Rev-1 vaccine was started in 1998, the human incidence again decreased. The association of the vaccination coverage of animals and incidence of brucellosis in humans was not linear; the decrease in human brucellosis incidence was observed when the vaccination coverage of animals was >30%.     

Use of the brucellosis card test for screening cattle in Saskatchewan.

One group of 28,714 bovine sera were tested by both the brucellosis tube serum agglutination test and the brucellosis card test. The tube serum agglutination test confirmed 99.8% of the negative brucellosis card test results. The brucellosis card test identified 63% of the tube serum agglutination test reactors. In a second group of 496 sera reacting to either the tube serum agglutination test, complement fixation test, plate serum agglutination test or acid antigen serum agglutination test the brucellosis card test identified 99.1% of the complement fixation test positive sera and 91.3% of the sera reacting to any of the other serological tests. The brucellosis card test showed satisfactory agreement with both the complement fixation test and tube serum agglutination test. It appears to be a useful screening test in operations involving large numbers of animals since under these conditions the reactors can be quickly identified and isolated.     

Risk associated with animals moved from herds infected with brucellosis in Northern Ireland

The movement of cattle from herds infected with Brucella abortus was investigated in order to assess the control measures for eradication of brucellosis from the cattle population of Northern Ireland. Using recorded cattle movement data, a historical cohort study was designed and carried out to quantify the risk of seropositivity in bovine animals moved from herds infected with brucellosis. The study found that 3.1% of animals, moved in the 6-month period prior to disclosure of infection in the source herd and subsequently tested, were interpreted as seropositive in their destination herds. The odds of seropositivity were approximately 19 (95% confidence interval: 7.8-46.4) times higher in this cohort compared with animals from herds with no history of infection. A multivariate logistic regression model was constructed to examine factors influencing the risk of seropositivity in the exposed cohort of animals, identifying maternal status (whether the dam had been a brucellosis reactor) and age at leaving the infected herd as the main risk factors.