Dynamics of Moraxella bovis infection and humoral immune response to bovine herpes virus type 1 during a natural outbreak of infectious bovine keratoconjunctivitis in beef calves

Assessment of Cidofovir for Treatment of Ocular Bovine Herpesvirus-1 Infection in Cattle Using an Ex-Vivo Model

Bovine herpesvirus-1 (BoHV-1) infection contributes to keratoconjunctivitis, respiratory disease, and reproductive losses in cattle. The objective of this study was to determine the most appropriate ophthalmic antiviral agent for BoHV-1 inhibition using in-vitro culture and novel ex-vivo bovine corneal modeling. Half-maximal inhibitory concentrations of BoHV-1 were determined for cidofovir, ganciclovir, idoxuridine, and trifluridine via in-vitro plaque reduction assays. In-vitro cytotoxicity was compared amongst these compounds via luciferase assays. Trifluridine and cidofovir were the most potent BoHV-1 inhibitors in vitro, while trifluridine and idoxuridine were the most cytotoxic agents. Therefore, cidofovir was the most potent non-cytotoxic agent and was employed in the ex-vivo corneal assay. Corneoscleral rings (n = 36) from fresh cadaver bovine globes were harvested and equally divided into an uninfected, untreated control group; a BoHV-1-infected, untreated group; and a BoHV-1-infected, cidofovir-treated group. Virus isolation for BoHV-1 titers was performed from corneal tissue and liquid media. Histologic measurements of corneal thickness, epithelial cell density, and tissue organization were compared between groups. Substantial BoHV-1 replication was observed in infected, untreated corneas, but BoHV-1 titer was significantly reduced in cidofovir-treated (1.69 ± 0.08 × 10³ PFU/mL) versus untreated (8.25 ± 0.25 × 10⁵ PFU/mL, p < 0.0001) tissues by day 2 of culture. No significant differences in histologic criteria were observed between groups. In conclusion, cidofovir warrants further investigation as treatment for BoHV-1 keratoconjunctivitis, with future studies needed to assess in-vivo tolerability and efficacy.

Perceptions and practices of Australian cattle farmers for the treatment of pinkeye (infectious bovine keratoconjunctivitis)

Pinkeye or infectious bovine keratoconjunctivitis is a globally significant disease and occurs in every state of Australia. Economic loss due to pinkeye can be considerable and it is a major welfare concern, but not all cattle with the disease are treated by farmers. This study was conducted to understand the perceptions and practices of Australian farmers regarding the treatment of pinkeye: factors influencing when farmers treat pinkeye, treatments used and considered effective, and reasons for not treating. Data were gathered using a custom designed online questionnaire. Farmer responses suitable for assessment (n = 985) were analysed using descriptive analyses along with univariable and multivariable ordinal logistic regression models to evaluate the association of 15 explanatory variables with the outcome "when do you treat pinkeye?". Results revealed three variables, farm size, times yarded and ranking of the pain caused by pinkeye, were significantly associated with the frequency of pinkeye treatment. Specifically, farmers with smaller farm sizes were more likely to treat their cattle for pinkeye more frequently. So too were those who yarded their cattle more, and those that rated pinkeye as highly painful. The most used treatments for pinkeye in Australia were pinkeye ointments (n = 861), followed by eye patches (n = 637), pinkeye spray (n = 623), fly control (n = 507), and pinkeye powder (n = 408). Over half of those who had used subconjunctival injection, pinkeye ointments, eye patches, injectable antibiotics and veterinarians rated them as highly effective treatments. Kerosene is still used by some farmers (n = 106). The most common reason for not treating pinkeye was that it was 'too difficult to treat individuals'. These findings provide insight into the attitudes of Australian farmers to the treatment of pinkeye and should be used to improve pinkeye outcomes in cattle.

Risk factors associated with pinkeye in Australian cattle

Pinkeye is the most important bovine ocular disease worldwide and a major welfare and economic concern to the Australian cattle industry. Pinkeye can occur in epidemic proportions, but severity and susceptibility vary within and between herds, indicating that the disease is multifactorial. This study was conducted to identify the on-farm risk factors associated with pinkeye disease in Australian cattle. Data were gathered from cattle farmers using a custom designed online questionnaire. Farmer responses suitable for assessment (n = 999) were analysed with descriptive, univariable and multivariable logistic regression to evaluate the association of 26 explanatory variables with pinkeye within-herd prevalence. Results revealed that farm location, farm grazing area, farmer-reported dust levels, fly levels, rain levels, animal zebu content and cattle age were significantly associated with pinkeye prevalence. More specifically, having a farm located in southern Australia, of smaller grazing area with cattle ≤ 2 years of age, was associated with a higher pinkeye prevalence. Pinkeye prevalence was also greater if respondents ranked their farms as having high fly levels compared to moderate and low fly levels, respectively and on farms ranked low for rainfall compared to moderate and high rainfall, respectively. Those that ranked their farms as having high dust levels had more pinkeye compared to moderate and low dust levels, but moderate dust levels were protective compared to low dust levels. The results confirm that pinkeye disease is multifactorial and is associated with a range of host and environmental factors. These findings should be used to assist in the control of the disease and improve pinkeye outcomes in Australian cattle.

Current incidence, treatment costs and seasonality of pinkeye in Australian cattle estimated from sales of three popular medications

Pinkeye is an economically important ocular disease occurring in all cattle producing areas of Australia. This study was undertaken to estimate the frequency of occurrence of the disease in Australia and treatment costs of the disease to the cattle industry using the sales of popular pinkeye medications as a surrogate indicator. Monthly sales data for Orbenin® Eye Ointment, Opticlox® Eye Ointment and Terramycin® Pinkeye Aerosol were analysed. We first estimated the number of cattle that can be treated with a syringe or a can and then using the data of sales of these pinkeye medications and the total cattle population of Australia, estimated the incidence of pinkeye. Probability distributions were used to include uncertainty around the estimates. Costs to producers were estimated based on retail prices of these medications. The results indicated that 732,864 syringes of Orbenin® Eye Ointment, 134,800 syringes of Opticlox® Eye Ointment and 27,755 cans of Terramycin® Pinkeye Aerosol are sold in Australia per year. Based on some assumptions of the number of cases treated by these drugs and number of cases left untreated, the number of cattle affected by pinkeye each year in Australia was estimated to be 2.80 million (95 % PI: 1.76, 4.65) or 10.25 % (95 % PI: 6.43, 16.97) of the entire Australian cattle herd. The cattle industry is expected to lose AU$ 9.67 million (95 % PI: 8.56, 13.11) each year just considering the cost of these three drugs. The results suggest that losses due to pinkeye in the Australian cattle industry are considerably higher than previously thought and should be used to inform the development of disease prevention and control policies.

A multiplex real-time PCR assay for the detection and differentiation of five bovine pinkeye pathogens

Infectious bovine keratoconjunctivitis (IBK), also known as pinkeye, is one of the most common eye diseases in cattle. Several pathogens have been associated with IBK cases, however, Moraxella bovis, Moraxella bovoculi, Mycoplasma bovis, Mycoplasma bovoculi and bovine herpesvirus type 1 (BHV-1) are most frequently observed. A multiplex real-time PCR assay using two reactions was developed for the detection and differentiation of these five pathogens. Detection sensitivities of the multiplex assays were compared to singleplex reactions testing for the same targets. Correlation coefficients (R²) of >0.99, and PCR efficiencies between 92 and 106% were demonstrated in all singleplex and multiplex real-time PCR reactions. The limits of detection (LOD) of multiplex assays for Moraxella bovis, Moraxella bovoculi, Mycoplasma bovis, Mycoplasma bovoculi and BHV-1 were 19, 23, 25, 24 and 26 copies per reaction, respectively. No cross amplification was observed for specificity testing of 179 IBK positive clinical samples and 55 non-target clinical samples. Percentage of clinical samples positive for Mycoplasma bovoculi, Moraxella bovoculi, Moraxella bovis, BHV-1 and Mycoplasma bovis were 88.8% (159/179), 75.9% (136/179), 60.3% (108/179), 11.7% (21/179) and 10.0% (18/179), respectively. Moraxella bovis, Moraxella bovoculi and Mycoplasma bovoculi were more prevalent than Mycoplasma bovis and BHV-1 in IBK samples collected from animals in this study population. Our data indicates that the multiplex real-time PCR panel assay is highly sensitive and highly specific for the detection and differentiation of the five major pathogens associated with bovine pinkeye.

•

A multiplex real-time PCR is developed for the detection of five major IBK pathogens.

•

Correlation coefficients of all standard curves were >0.99.

•

PCR amplification efficiencies for the five pathogens were between 92% and 106%.

•

Limits of detection were between 19 and 26 copies per reaction for the five pathogens.

•

Moraxella bovoculi, Mycoplasma bovoculi, and Moraxella bovis were more prevalent IBK pathogens.

Infectious keratoconjunctivitis in semi-domesticated Eurasian tundra reindeer (Rangifer tarandus tarandus): microbiological study of clinically affected and unaffected animals with special reference to cervid herpesvirus 2

Background

Infectious keratoconjunctivitis (IKC) is one of the most common ocular diseases in ruminants worldwide. In addition to keratitis and conjunctivitis, animals with IKC can develop uveitis, corneal ulcer, and in severe cases, blindness. The bacteria Moraxella spp. has been described as the primary causative agent of infectious bovine keratoconjunctivitis (IBK) in cattle (Bos taurus), while Chlamydia spp. and Mycoplasma conjunctivae are considered the main causative agents of IKC in sheep (Ovis aries). Previous studies indicated cervid herpesvirus 2 (CvHV2) as the primary causative agent of IKC in semi-domesticated reindeer (Rangifer tarandus tarandus). The aim of the study was to investigate the presence and prevalence of potential pathogens for IKC in reindeer, and compare the ocular microbiota of animals with IKC, with apparently healthy animals.

Results

Semi-domesticated reindeer (n = 341), with (n = 108) or without (n = 113) ocular clinical signs, or with no information on clinical status (n = 120), were sampled in Norway, Sweden and Finland in 2010–2014. Seroprevalence was 37.4% for alphaherpesvirus (95/254), 3.8% for gammaherpesvirus (8/211) and 7.1% for pestivirus (15/211) (ELISA). PCR analyses of conjunctival swab samples revealed a prevalence of 28.5% for CvHV2 (57/200), 11.9% for Chlamydiaceae (16/135) and 1.0% for M. conjunctivae (2/197). Bacteriological cultivation of 202 conjunctival swab samples revealed bacterial growth from 75.2% of the samples, with Moraxella spp. being isolated from 21.6% (11/51) of the animals with and 5.6% (5/84) without ocular clinical signs. A significant association (p < 0.001) existed between the presence of clinical signs of IKC and CvHV2 DNA in the affected eyes, an association that was not present for other microorganisms.

Conclusions

These results support the hypothesis that CvHV2 is the primary agent of IKC in semi-domesticated reindeer in Fennoscandia, with Moraxella bovoculi being a secondary candidate, since it was isolated in two different outbreaks of IKC. Further studies should be carried out to better understand the infection biology and the pathogenesis of IKC in reindeer.