This report describes two cases of malignant catarrhal fever (MCF) that occurred one month apart in a small herd of Angus heifers located in the Forbes region, Central West NSW. Presentation of the two heifers was very similar with predominant signs of initial blindness associated with bilateral ocular lesions, then inappetence and rapid progressive loss of body condition and development of neurological signs including circling over several weeks. An interesting aspect of these cases was the absence of erosive stomatitis, which is a common feature of acute MCF.
A mixed farming producer purchased 24 Angus heifers from the Central Tablelands Livestock Exchange at Carcoar in September 2022. The cattle were run on a 130-hectare property, grazing mixed perennial pastures with intermittent access to piles of old water-damaged rotting hay. There was also a mob of trade lambs grazing in adjacent paddocks on the property.
The producer noticed shortly after the cattle arrived that one heifer had two 'white eyes', however she appeared to be well otherwise. He treated her for pink eye with Terramycin® Pinkeye Aerosol (oxytetracycline hydrochloride 2mg/g in a non-CFC propellant). There was no apparent improvement to the eye lesions, however as there was no progression of signs, no further treatment was administered.
In May 2023, after a short trip away from the farm, the producer returned to find the same heifer had lost a significant amount of body condition and was circling in the paddock with 'pink things' coming out of her eyes. He separated her from the rest of the herd and yarded her to treat the eyes with a topical antibiotic ointment. The Local Land Services District Veterinarian (LLS DV) was contacted after approximately a week and a half of further deterioration.
On inspection the heifer was in poor body condition with mild serous nasal discharge and mild, green diarrhoea. She had prominent bilateral ocular protuberances, appeared completely blind and was exhibiting horizontal nystagmus. She became distressed and circled compulsively when disturbed.
On physical examination in the crush her temperature was 38.9° Celsius. The remnant cornea of both eyes was blue with extensive neovascularisation, and the ocular protuberances appeared to be from corneal rupture and protrusion of internal contents.
Blood samples were taken to test for persistent pestivirus infection. As the case was isolated and due to the chronic history, the ocular lesions were attributed to infectious bovine keratoconjunctivitis (IBK) and the weight loss and circling secondary to complete blindness. No further testing was undertaken and it was recommended to euthanise the heifer on welfare grounds. Pestivirus antigen PACE results were negative.
One month later the producer found a second heifer blind with 'white cloudy eyes' and rapid significant weight loss. She was also circling, and periodically holding her head straight up in the air, similar to 'star gazing'. Assuming this heifer also had IBK, the producer yarded her and treated the ocular lesions with antibiotic ointment for a week with no improvement. After reporting this second case to the LLS DV, the previous diagnosis in the first heifer was questioned and the decision made to euthanise the second heifer and perform a full necropsy.
On examination in the yards the heifer was alert, but in poor body condition and appeared to be completely blind. With stimulation, she would circle and became aggressive when moved into the crush.
On physical examination in the crush, her rectal temperature was 38.7° Celsius and she had a mild thick mucopurulent nasal discharge. Both eyes were abnormal with markedly thickened corneas. The right eye was completely opaque and a yellow, red-tinged colour. In addition, the left cornea had been traumatically ruptured a week previously on a tree branch and the eye was partly sunken.
Ante-mortem blood samples were collected, and the heifer was euthanised by sedation and captive bolt.
On post-mortem examination, the only significant finding was a moderately inflamed abomasal mucosa with multifocal, puckered scar-like lesions. It was noted that there were no oral mucosal erosions or other abnormalities on oral examination. Dry and Amies swabs were taken from the unruptured eye for culture and then the eye was fixed in formalin. Fixed and fresh samples were also taken from multiple organs and the brain, although the brain was significantly damaged by the captive bolt euthanasia.
Differential diagnoses considered were IBK, ocular listeriosis, pestivirus and malignant catarrhal fever (MCF). Intestinal parasites were considered a possible cause of the abomasum lesions.
Pestivirus PACE testing and listeria eye swab culture were negative. Aerobic culture of the eye swab yielded no significant growth whilst the bovine pinkeye PCR panel detected Moraxella bovis. Histopathology on the eye and abomasum identified the following morphological diagnoses:
The lymphoproliferative vasculitis and perivasculitis was considered highly suspicious of infection with Ovine Herpesvirus 2 (OHV-2) in cattle and MCF Virus PCR returned a positive result.
MCF is usually an acute, fatal yet sporadic disease of cattle. Multiple expressions of the disease are described, however the most common is the 'head and eye' form which involves persistent fever, inappetence, ocular and nasal discharge, bilateral keratitis, erosions of the oral cavity and muzzle, diarrhoea and depression. Consequently, differential diagnoses such as foot-and-mouth disease (FMD), mucosal disease, infectious bovine rhinotracheitis and other vesicular type diseases are often considered. Although uncommon, there are reports of chronic disease due to MCF in cattle and even recoveries of some affected animals.
Although unable to be confirmed through retrospective diagnostic testing, it is considered highly likely that heifer 1 also had MCF due to the similarities in presentation and clinical course between the two animals. Interestingly, both heifers seem to have had a more chronic and milder presentation of the virus, with the absence of significant fever and mucosal lesions on physical examination. For this reason, MCF and vesicular diseases such as FMD were not considered as differential diagnoses initially. The ocular lesions of both heifers were more advanced and chronic in presentation than what are often seen in acute cases of MCF. Corneal ulceration and rupture have been reported to occur in chronic and recovering cases of MCF, as well as chronic weight loss.
Sheep are considered the reservoir source of OHV-2 and reports of transmission to cattle are often following contact with pregnant or lambing ewes. These cattle were grazed next to trade lambs since they were introduced to the property. Interestingly, the producer noted heifer 1 had clouded eyes on arrival to the property in September 2022. If it is assumed this date corresponds to the onset of keratitis due to infection with OHV-2 the clinical presentation would have progressed over an eight-month period.
As this case demonstrates, there is the potential for chronic cases of MCF in cattle to be under-diagnosed. The MCF PCR test is simple to perform on EDTA whole blood and has a high sensitivity and specificity. It may be worthwhile to use this test to diagnose or rule out MCF in cattle showing clinical signs such as bilateral ocular disease and chronic weight loss.