Interesting cases in June

Cattle
Abortions and mastitis

• Bacillus licheniformis, Campylobacter fetus, Salmonella Dublin, Streptococcus infantarius and Trueperella pyogenes were cultured from stomach contents of aborted bovine foetuses this month. Streptococcus infantarius is an enteric commensal, which can act as an opportunistic pathogen and was considered the likely cause of abortion in that case.
• In three cases, foetal fluid tested positive for antibodies to Neospora caninum indicating the calves had seroconverted in utero. The finding however is not sufficient to diagnose neosporosis as the cause of the abortion – that requires histopathology of foetal heart and brain.
• In one submission, pooled foetal tissues and placenta only from an aborted cow tested positive for both Neospora caninum and Coxiella burnetiion PCR testing. A total of three cows had aborted in the same week on the farm at around 150 days of gestation.
• Foetal tissue from an aborted calf tested positive for BVD virus by PCR. There was known active BVD infection on the farm at the time of the abortion.
• Isolates in cases of mastitis in June included Trueperella pyogenes, Staphylococcus aureus, Corynebacterium bovis, Streptococcus uberis, Streptococcus dysgalactiae, Escherichia coli, Acinetobacter sp, Serratia sp and Lactococcus lactis. More unusual isolates from bovine milk which were considered of significance included Pasteurella multocida, Lysinibacillus sp and Nocardia paucivorans.

Respiratory disease

• Bovine coronavirus was detected in at least 12 submissions for investigation of bovine respiratory illness either as the sole pathogen detected or in combination with other viruses or bacterial pathogens.
• PI3 was detected three times by PCR and, in all three cases, bovine coronavirus was also detected.
• RSV was recorded in four cases and in two of these bovine coronavirus was also detected. RSV virus and coronavirus were detected in pooled PCRs of nasopharyngeal swabs from four-month-old weaned calves that were showing a poor response to oxytetracycline and meloxicam treatment.
• A significant increasing antibody level to RSV virus was demonstrated on paired serology from a two-year-old Holstein indicating recent exposure.
• One case of IBR was identified by PCR testing of nasopharyngeal swabs on one farm suffering an outbreak of severe respiratory disease. On another holding, vaccinal IBR virus (gE deleted) was detected in swabs from calves that had recently reived an intranasal IBR vaccine. The extended respiratory pathogen PCR package can differentiate between marker vaccine and wild type IBR virus.
• Mannheimia haemolytica was detected by PCR testing on lung tissue from a PME of a calf that was one of a group showing signs of pneumonia.
• Mannheimia haemolytica was cultured from lung tissue from an adult dairy cow in a herd where cows were reported to be losing condition. Observations on histopathology were of a severe bacterial bronchopneumonia consistent with the bacteriology findings.
• Pasteurella multocida was cultured from lung tissue of a female calf that had sudden onset of dyspnoea and died. Severe lung pathology was observed at PME.
• Lung tissue was received for histopathology from a two-month-old Limousin cross calf which was purchased with its dam at market but was found dead in the trailer on arrival. Cranioventral consolidation was observed at PME with some emphysematous bullae present. Microscopic changes seen in the lung tissue were severe, chronic and ongoing and consistent with enzootic calf pneumonia/bovine respiratory disease (BRD). Due to the chronic and established nature of the lesions, it was not possible to confirm or rule out any particular underlying pathogen. Bronchiolitis fibrosa obliterans was observed and indicates a severe necrotising bronchiolitis that in this age of calf is normally associated with a previous pneumotropic viral infection such as BHV 1, RSV and PI 3. Evidence of secondary bacterial infection was seen and likely pathogens included Pasteurella multocida, Mannheimia haemolytica, Histophilus somni and Trueperella pyogenes. In addition, a plasmalymphocytic periairway infiltrate indicated likely concurrent mycoplasma infection that could include Mycoplasma bovis, dispar, canis, canadensis and/or alkalescens.
• A fibrinous bronchopneumonia with superimposed bronchointerstitial pneumonia was identified on histopathology of lung from a four-month-old Aberdeen Angus cross suckler calf that had been turned out one week previously and developed acute onset dyspnoea with death after 48 hours. A bacterial pathogen such as Mannheimia haemolytica was the suspected cause of the bronchopneumonia component. Further to this an interstitial component was evident. This pattern of interstitial pneumonia can be seen secondary to established bronchopneumonia in cranioventral lung lobes in growing animals. No underlying microbial cause was established for this change and this is a phenomenon that has been associated with bronchopneumonia; some theories suggest a cytokine storm as the pathogenesis.
• Acute Respiratory Distress Syndrome (ARDS) was found to be the cause of death in a one-day-old calf that was one of two in the same herd that were born weakly and died soon after birth. It was reported that the lungs appeared poorly inflated and were consolidated and the liver had a yellow appearance. Histopathological examination found evidence of aspirated meconium, which is commonly associated with foetal stress at the time of parturition. This can adversely affect surfactant activity resulting in only partial alveolar inflation with subsequent respiratory distress. Other factors including prematurity and foetal hypothyroidism could potentially be implicated in reduced surfactant secretion/activity. It was however noted that these histological changes are indistinguishable from damage mediated by pneumotoxic agents, smoke inhalation, and acute severe respiratory viral infections etc. Severe hepatic necrosis was present and possible suggested causes included hypoxia (and this is often worse in animals that die slowly and/or were anaemic) or a toxic insult. Hypoxia was considered most likely in this case given the severe changes in the lung.

A necrotic terminal airway (arrows) in the lung of a calf with acute respiratory distress syndrome

• An adult dairy cow tested positive for antibodies to Mycoplasma bovis with a high antibody level suggestive of recent exposure after showing signs of pyrexia, an increased respiratory rate and a swollen carpal joint of 10 days duration. The submitting vet reported that the herd had many similar cases in the past with evidence of seroconversion to Mycoplasma bovis. Underlying poor immune system function can sometimes be involved in outbreaks involving adults e.g. active BVD virus infection or nutritional deficiencies, such as vitamin A or protein.
• Patent lungworm (D. viviparus) was diagnosed in several herds using Baermann’s examination of faecal samples. One case was in a group of fattening bullocks that were in their first grazing season, had been outside since April and had developed prolonged coughing with pyrexia and one affected animal was described as having an expiratory ‘squeak’. On a different holding, two-year-old in-calf dairy heifers had recently started coughing. The vet suspected that the animals had reduced development of immunity to lungworm due to previous treatment with long acting moxidectin injection. Larvae with appearance consistent with D. viviparus were seen on Baermann’s examination.

Gastrointestinal disease

• A total of 416 submissions for Johne’s disease serology and faecal PCR testing from cattle were received this month, with 136 submissions, including a total of 210 individual samples, testing positive.
• Parasitic gastroenteritis was the likely cause of scour in five of a group of 80 yearling cattle which had a pooled faecal egg count of 1950epg strongyle sp.
• A two-year-old British Blue animal was reported to be much poorer than others in its group over the last month. The pepsinogen level was high at 8.7iμ/l (reference value <1.5iμ/l) indicating there was significant abomasal parasitism.
• Coronavirus antigen was detected in the faeces of scouring Jersey and South Devon calves.
• A faecal sample from a calf which died due to scour at two weeks of age tested positive for both rotavirus and coronavirus antigen.
• Coccidiosis was suspected based on high coccidial oocyst counts and clinical signs on at least six occasions. One case was a well-grown bull calf that suddenly developed bloody scour and had a high coccidial oocyst count. In another case, female Holstein calves developed a bloody scour at around four weeks of age. The coccidial oocyst count was >50,000epg faeces. Coccidial oocyst speciation was not carried out to confirm the diagnosis.
• Salmonella Dublin was isolated in seven submissions this month. Salmonella Typhimurium was isolated on two occasions and Salmonella Mbandaka and Salmonella Montevideo were each isolated in one submission. In one of the cases of Salmonella Typhimurium, a group of far-off dry cows showed reduced rumen activity in the past week, a few had blood in faeces and four seen by the vet appeared sick and depressed. There had been previous history of Salmonella infection on the farm but not in recent times.
• There were five cases of fasciolosis, three of which also had rumen fluke eggs present in the samples. One submission included faecal samples from five animals of which two tested positive and one was suspicious in the liver fluke coproantigen ELISA, though no fluke eggs had been seen on microscopy at the practice. On another farm, one of two dairy heifers that were 50 DIM, tested positive for antibodies to liver fluke on serology. They had been doing well but had a significant drop in yield, had lost condition and had a poor hair coat. In another herd, two Holstein-Friesian dairy cows tested positive for antibodies to liver fluke. One was reported to be losing weight in mid-lactation, the other was failing to get in-calf.

Skin and eye disease

• Skin biopsy samples were received from a two-year-old Charolais cross beef finisher animal. It was one of five in the group that had shown signs of external lymph node abscessation around the head and prescapular lymph nodes. Histopathology identified a focally extensive, severe, chronic-active, pyogranulomatous lymphadenitis with intralesional Splendore Hoeppli material and gram-negative coccobacilli bacteria. The changes seen were considered consistent with an inflammatory reaction associated with chronic bacterial infection. The organism morphology was most consistent with Actinobacillus lignieresii that is usually associated with wooden tongue in cattle and it can cause cutaneous actinobacillosis. A. lignieresii is a normal commensal organism in the oral cavity of cattle. Lymphadenitis, lymph node abscesses, and infectious granulomas originating from lymph nodes may follow soft tissue infections of the oral cavity or pharynx. Extremely fibrous feed material has been incriminated as the cause of mucosal injury in previously documented cases. On another farm, lymph node related masses in cattle were also suspected to be due to the cutaneous form of actinobacillosis. In this case, an Actinobacillus sp. was isolated in cultures of aspirated material from the abscesses.
• Moraxella bovoculi was isolated in three cases of Infectious keratoconjunctivitis (IKC) in cattle. In one of the cases, 15 of 25 heifers in a group were affected and the submitting vet commented that the same shed had this problem every year.

Systemic and miscellaneous disease

• A total of 420 submissions were received for BVD antigen testing in cattle in February, with 33 submissions, including a total of 51 individual samples, testing positive.
• A dairy herd that had recently seroconverted to Leptospira Hardjo in the bulk milk serology test, performed further individual blood testing on six unvaccinated cows all of which were strongly antibody positive to Leptospira Hardjo in the ELISA.
• Babesiosis was diagnosed on three occasions in June, in Dorset, Wiltshire and Northumberland. One of the cases was a six-year-old Hereford cow, which was found dull in the field, was passing very dark urine and the mucus membranes appeared congested and jaundiced. Blood parasites with an appearance consistent with Babesia divergens were seen on blood films.
• Helcococcus ovis was isolated from a joint fluid sample from a Salers heifer calf with joint ill that was failing to respond to antibiotic treatment.
• OvHV-2, the viral cause of Malignant Catarrhal Fever, was detected by PCR in six cases. One affected British Blue cow had persistent pyrexia despite treatment and developed an initially clear ocular discharge that progressed to a mucopurulent nasal discharge and cloudy cornea in one eye. Sheep, which are commonly asymptomatic carriers of OvHV-2 virus, were also present on the holding. On another farm, an Aberdeen Angus cross cow which showed typical clinical signs of MCF tested positive for antibody to OvHV-2 confirming exposure to the virus. Some of these MCF cases were also undergoing investigations for BTV by APHA at the same time as MCF testing as the two conditions can have some clinical similarities (e.g. pyrexia, swollen heads and crusting around the nostrils).
• Pyogranulomatous nephritis was diagnosed on histopathology of renal tissue from a two-month-old beef suckler heifer calf. Gross lesions were observed at PME and histopathology identified a multifocal to coalescing, severe, chronic-active, pyogranulomatous nephritis. Possible suggested differential diagnoses included bacterial infection, fungal infection, mycobacteriosis or potentially toxicosis. A bacterial infection such as Rhodococcus equi (rare in cattle, common in horses) was also considered possible. It was noted that some toxins (e.g. hairy vetch and citrus pulp toxicosis) could cause similar changes.
• Melanoma was diagnosed by histopathology of a mass removed from the skin of a ten-month-old Holstein heifer. Dermal melanocytic tumors make up 5-6% of tumours developing infrequently anywhere on the body. Most cattle that are affected have red, black or grey hair coats and Angus cattle appear predisposed. Unlike companion animals where these tumours tend to occur in older animals, bovine melanocytic tumours tend to occur in younger animals although can be found at any age. The tumours are most often benign, thus classifying them as melanocytoma rather than a malignant melanoma and they are often large nodular masses, densely pigmented on cut surfaces. Excision is curative for most; however, there are rare reports of locally invasive tumors as well as metastasis to distant sites.