Epidemiological and clinicopathological findings in 15 fatal outbreaks of salmonellosis in dairy calves and virulence genes in the causative Salmonella enterica Typhimurium and Dublin strains

Salmonella enterica is a major food-borne pathogen that affects cattle-rearing systems worldwide. Little information is available on the epidemiology and pathology of salmonellosis and the virulence genes (VGs) carried by Salmonella in spontaneous outbreaks in cattle. We describe epidemiological findings in 15 fatal outbreaks of salmonellosis in Uruguayan dairy farms and the age, clinical signs, and pathology in 20 affected calves. We also describe the serotypes and frequencies of 17 VGs in the causative Salmonella strains and explore their associations with epidemiological, clinical, and pathological findings. Salmonella Typhimurium and Dublin were identified in 11/15 and 4/15 outbreaks, respectively. The most frequent reason for consultation was digestive disease (8 outbreaks caused by S. Typhimurium), followed by sudden death (4 outbreaks, 3 caused by S. Dublin). Morbidity, mortality, and lethality ranged 4.8-100%, 3.8-78.9%, and 10-100%, without significant differences between serotypes. Diarrhea, the most common clinical sign (14 cases), was associated with the Typhimurium serotype (OR = 26.95), especially in ≤ 30-day-old calves with fibrinous enteritis as the main autopsy finding. The Dublin serotype affected ≥ 50-day-old calves and was associated with fibrinosuppurative splenitis (p = 0.01) and tubulointerstitial nephritis (OR = 48.95). The chances of the Dublin serotype increased significantly with age. There was low variability of VG across serotypes. The pefA gene was associated with the Typhimurium serotype (OR = 21.95), macroscopic enteritis (p = 0.03), and microscopic fibrinosuppurative splenitis (p = 0.04). Understanding the epidemiology, pathology, and virulence of S. enterica at the farm level is key to delineating prevention and control strategies to mitigate its impact on animal and human health.

A holstein heifer infected with Neospora caninum NcUru3 congenitally transmits this strain to a viable offspring although infection does not protect her from aborting by a different N. caninum genotype in the subsequent gestation

Neospora caninum is a leading cause of bovine abortion worldwide. Although the genetic diversity of this apicomplexan parasite has long been recognized, there is little information on whether infection with different genotypes results in different clinical outcomes or whether infection by a given genotype impairs protective immunity against abortion induced by different genotypes. Here, we provide evidence supporting that natural subclinical infection with isolate NcUru3 of N. caninum in a pregnant heifer did not provide protection against abortion caused by a different N. caninum genotype in the subsequent gestation. A Holstein heifer delivered a healthy calf congenitally infected with N. caninum. Specific anti-N. caninum IgG was detected by indirect ELISA in sera obtained from the dam at calving and the calf before ingestion of colostrum, indicating in utero exposure to the parasite in the latter. A N. caninum strain named NcUru3 was isolated and characterized by multilocus microsatellite typing from the brain of this neonate euthanized at 9 days of age. Sixty days after calving, the cow got pregnant, although she aborted spontaneously at ~6 months of gestation. Pathologic examination of the aborted fetus and placenta revealed typical lesions of neosporosis, including encephalitis, myocarditis, hepatitis, myositis, and placentitis. Neospora caninum DNA was amplified from the fetal brain, heart, kidney, and placenta, and multilocus microsatellite typing revealed a genotype that differed from isolate NcUru3 at the level of microsatellite marker 6A (MS6A). Serum obtained from the dam at the time of abortion had IgG that cross-recognized isolate NcUru3, as demonstrated by immunoblotting, indicating that the humoral immune response did not prevent the other genotype from infecting the fetus and inducing fetoplacental lesions and abortion. This is the first description of one same dam transmitting two N. caninum genotypes to her offspring in subsequent gestations.

Diagnostic Investigation of 100 Cases of Abortion in Sheep in Uruguay: 2015–2021

The aim of this work was to identify causes of abortion through laboratory investigations in sheep flocks in Uruguay. One hundred cases of abortion, comprising 58 fetuses, 36 fetuses with their placentas, and 6 placentas were investigated in 2015–2021. Cases were subjected to gross and microscopic pathologic examinations, and microbiological and serological testing for the identification of causes of abortion, including protozoal, bacterial, and viral pathogens. An etiologic diagnosis was determined in 46 (46%) cases, including 33 (33%) cases caused by infectious pathogens, as determined by the detection of a pathogen along with the identification of fetoplacental lesions attributable to the detected pathogen. Twenty-seven cases (27%) were caused by Toxoplasma gondii, 5 (5%) by Campylobacter fetus subspecies fetus, and 1 (1%) by an unidentified species of Campylobacter. Fourteen cases (14%) had inflammatory and/or necrotizing fetoplacental lesions compatible with an infectious etiology. Although the cause for these lesions was not clearly identified, T. gondii was detected in 4 of these cases, opportunistic bacteria (Bacillus licheniformis, Streptococcus sp.) were isolated in 2 cases, and bovine viral diarrhea virus 1 subtype i (BVDV-1i) was detected in another. Campylobacter jejuni was identified in 1 (1%) severely autolyzed, mummified fetus. BVDV-2b was identified incidentally in one fetus with an etiologic diagnosis of toxoplasmosis. Microscopic agglutination test revealed antibodies against ≥1 Leptospira serovars in 15/63 (23.8%) fetuses; however, Leptospira was not identified by a combination of qPCR, culture, fluorescent antibody testing nor immunohistochemistry. Neospora caninum, Chlamydia abortus, Chlamydia pecorum, Coxiella burnetii and border disease virus were not detected in any of the analyzed cases. Death was attributed to dystocia in 13 (13%) fetuses delivered by 8 sheep, mostly from one highly prolific flock. Congenital malformations including inferior prognathism, a focal hepatic cyst, and enterohepatic agenesis were identified in one fetus each, the latter being the only one considered incompatible with postnatal life. Toxoplasmosis, campylobacteriosis and dystocia were the main identified causes of fetal losses. Despite the relatively low overall success rate in establishing an etiologic diagnosis, a systematic laboratory workup in cases of abortion is of value to identify their causes and enables zoonotic pathogens surveillance.

Placentitis and abortion caused by a multidrug resistant strain of Campylobacter fetus subspecies fetus in a sheep in Uruguay

Campylobacter fetusfetus (Cff) is a major infectious cause of abortion in sheep worldwide, and an opportunistic human pathogen. Information on Cff as an ovine abortifacient in South America is limited. We describe a case of abortion caused by a multidrug resistant strain of Cff in a sheep in Uruguay. In August 2017, 3/57 pregnant ewes (5.3%) aborted whithin one week. Histopathologic examination of the placenta of an aborted ewe revealed severe neutrophilic and fibrinonecrotizing placentitis with vasculitis and thrombosis of the chorionic arterioles. Cff was isolated on microaerobic culture in Skirrow agar, and further confirmed by 16S rDNA PCR amplification and sequencing, and endpoint and real time PCR assays. Antimicrobial sensitivity testing revealed resistance to tetracyclines, nalidixic acid, telithromycin and clindamycin. Other abortifacients were not detected. Further studies are necessary to determine the geographic distribution, ecology, epidemiology, economic impact, and antimicrobial resistance of Cff in sheep flocks in Uruguay.

Baccharis coridifolia poisoning in livestock in Uruguay

Baccharis coridifolia is one of the most common poisonous plants affecting livestock in Uruguay. Poisoning occurs when animals raised in areas free of B. coridifolia are transported to pastures containing the plant. Young stock become spontaneously averted to it after ingesting non-toxic amounts of the plant. As B. coridifolia is widespread in the country, farmers selling livestock report when animals have been raised in areas with the plant, meaning that they are naturally averted and will not ingest it if introduced in B. coridifolia-containing paddocks. Of 2456 farmers from 18 departments of Uruguay selling cattle through online auctions between June 2019 and May 2020, 78% mentioned that the animals they were selling were raised in grasslands containing B. coridifolia. However, only 35.8% of the farmers from three departments of Eastern Uruguay mentioned that their cattle were raised in grasslands with B. coridifolia. Herds from these departments presented 16.7 times (95% CI: 13.1-21.3; p < 0.001) more risk of not being naturally averted to B. coridifolia ingestion than the herds of the other 15 departments of the country. In this paper we review all outbreaks of B. coridifolia poisoning reported in livestock in Uruguay from 1911 to present. We also describe three outbreaks of poisoning, one in cattle and two in sheep that were poisoned in the same farms in which the animals were raised. Intoxication occurred when the animals raised indoors and/or in cultivated pastures without B. coridifolia were introduced into grasslands of the same farms containing B. coridifolia. Typical gastrointestinal lesions were observed in pathological examinations. Furthermore, two of three necropsied heifers showed severe acute nephrosis, which had not been reported previously in this poisoning.

Rhipicephalus microplus, babesiosis and anaplasmosis in Uruguay: current situation and control or elimination programs on farms

Rhipicephalus microplus causes high economic losses for Uruguay; the country is divided into a R. microplus-free area and an endemic area. The aim of this research was to evaluate the R. microplus and tick fever situation in Uruguay and the feasibility of implementing R. microplus control or elimination programs to reduce the number of infested farms. A representative survey was performed to determine the number of infested farms, the number of farms with outbreaks of tick fever and the control and preventive measures being used. Control or elimination programs using generational treatment were implemented on 30 farms. Previously, a situation diagnosis was performed by evaluating the background of each farm, identifying acaricide resistance, serologically evaluating the enzootic stability of tick fever, and analyzing the risk of R. microplus introduction to farms. According to the survey, R. microplus was present on 9544 (36%) farms, and 3436 (36%) of these farms experienced outbreaks of tick fever. Only 323 (9.4%) farmers used the tick fever vaccine. Of the 30 farms for which control or elimination programs were carried out, 18 reduced the number of treatments applied per year and six achieved the elimination of the cattle tick. It is concluded that by administering elimination or control programs, it is possible to reduce the number of infested farms and the number of treatments to maintain control. New surveys should be performed to measure the degree of technology adoption by farmers and to analyze the advances in tick control or elimination programs on farms.

Fatal Sarcocystis cruzi-induced eosinophilic myocarditis in a heifer in Uruguay

Sarcocystis spp. are causative agents of bovine eosinophilic myositis and/or myocarditis, which are chronic subclinical myopathies that are occasionally responsible for condemnation at slaughterhouses. Sarcocystis cruzi is a protozoan parasite of worldwide distribution transmitted by canids, most commonly associated with subclinical infection in cattle. Although S. cruzi infections can rarely lead to fatal systemic disease, fatal cardiac cases with confirmation of the etiologic diagnosis have not been reported, to our knowledge. We describe herein an unusual case of S. cruzi-induced fatal bovine eosinophilic myocarditis. A 22-mo-old, Holstein-Hereford heifer, in a group of 110 cattle on pasture, manifested growth retardation and died in February 2017. Autopsy revealed myriad yellow-green 1-3-mm coalescing foci, surrounded by fibrosis, affecting ~75% of the ventricular myocardium. Pulmonary edema, ascites, and hydrothorax were consistent with chronic congestive heart failure. Histology revealed severe eosinophilic, granulomatous, necrotizing myocarditis, with multinucleate giant cells, fibrosis, and mineralization. Numerous thin-walled protozoan cysts resembling Sarcocystis spp. were present in the necrotic foci and within the sarcoplasm of adjacent cardiomyocytes. PCR and sequencing of the 18S rRNA gene revealed 99.9-100% homology with S. cruzi. Sarcocystosis can be a rare cause of fatal myocarditis in cattle.