Paratuberculosis or Johne's disease is a chronic contagious gastrointestinal bacterial infection affecting mainly domestic ruminant species including cattle, sheep and goats. Economic losses are due to mortalities and carcass condemnations in abattoirs, although weight loss, decreased milk production and fertility and losses due to the costs of implementing preventive and control measures plus and delayed genetic gain may occur (Bastida and Juste, 2011).
Johne's disease is caused by various strains of Mycobacterium avium subsp. paratuberculosis (MAP), an intracellular Ziehl-Nielson positive organism that is relatively resistant to hostile environments and some disinfectants. In Spain, the prevalence of paratuberculosis infected dairy herds is considered to be 45.7% (Prieto et al., 2013). Laboratory tests for paratuberculosis include fecal culture, ELISA, PCR or IFN. However, the prolonged duration of faecal culture and the low and variable sensitivity of the serological tests are problematic, with a recent study identifying differences in animal prevalence in a farm varying from 33.9% to 66.5%, using ELISA or IFN respectively (Mohamed Anciones et al., 2013). Due to the immunological complexity and the prolonged subclinical period of the disease it is difficult to determine only one reference diagnostic test. In the subclinical stages the cellular immune response is the one having diagnostic value (PCR) and in clinical stages the humoral immune response against MAP has better sensitivity (ELISA) (Gilardoni et al., 2012).
Control of paratuberculosis is also difficult, with vaccination in Spanish dairy herds forbidden due concerns of potential interference with diagnostic tests for tuberculosis. For this reason control measures are limited to test and cull strategies to eliminate sources of infection and the implementation of management interventions to avoid contact between infected and susceptible animals.
To this end was implemented in Victoria (Australia) the three steps calf rearing program (Windsor and Whittington, 2010).
In this present paper we describe two clinical cases of bovine Johne's disease (BJD) that occurred in two dairy cattle farms in Zaragoza, Spain.
One Holstein cow from a dairy farm near the Veterinary Faculty of Zaragoza was referred to the Ruminant Clinical Services on October 2012. This herd comprises 140 milking cows, with medium production levels, adequate feed, good facilities and very good levels of welfare. The herd is self-replacing and has an adequate IBR, BVD and enterotoxemia vaccination program. The farmer advised that the cow was born in 2008 and found to have problems with fertility in early 2012, despite synchronization treatments and artificial insemination. Signs of clinical BJD were observed from July 2012 when the affected cow developed a profuse liquid diarrhoea despite absence of other clinical signs such as pyrexia or inappetance. Previous clinical cases of BJD has been observed and as the veterinary practitioner to the farm considered this may be another case of BJD, rectal swabs for fecal culture and blood samples for serum were taken. The treatment applied was oral rumenal flora (for 4 days) and marbofloxacin, without response. Serology for BJD was negative and one month later, spirochetes were isolated in feces but MAP culture was also negative. As clinical signs progressed the milking ceased and the cow was sent to the dry cows herd. The practitioner submitted another sample and she was treated again with rumenal flora and centiofluor, again without response. Ten days later, another cow that had been born at approximately the same time as the affected was also observed to display similar clinical signs.
On October 2012 the second culture and serology was also negative for BJD and the practitioner submitted the animal to the Faculty. On examination the body condition score was 1.5, body temperature was low (37.3°C), and a mild bradycardia (50 ppm) and arrhythmia, sero-mucinous runny nose, pale mucous membranes and severe diarrhoea were noted (Figure 1) and routine hematology indicated anemia (22.3% HTC). Because these signs suggested BJD, a PCR to detect M. avium subsp. paratuberculosis in feces was attempted and found positive and a PCR on the second cow was also positive.
Due to the poor clinical condition the cow was euthanatised and a necropsy performed. Macroscopically, the most important findings were thickening of the mucosa of the jejunum, ileum and caecum portions suggestive of granulomatous enteritis and enlarged mesenteric lymph vessels (Figure 2). Widespread interstitial emphysema was noted in the lungs.
The microscopic findings of the bowel wall confirmed the presence of granulomatous enterocolitis with lymphocyte infiltration, fibrosis plus multinucleated giant cells containing clumps of elongated Ziehl-Neelsen positive forms compatible with mycobacteria.
A high production dairy farm from Alfajarin, a village near Zaragoza, has a major problem with BJD. The first case on this farm of 100 cows was identified 5 years ago after an affected cow was placed with heifers and in the following years, the majority of those heifers developed the disease. The farmer was concerned about the disease and decided to implement an eradication program. All cows were bleed for serology and positive animals that showed the most minimal symptoms of BJD were culled. Initially the prevalence was estimated at around 5-6%. The sero-positive animals that became ill were culled as were sero-negative animals that showed clinical signs of BJD, resulting in culling due to BJD of approximately 12% each year, imposing a significant economic loss for the farmer. In 2013, 20% of the animals in the herd are positive to serology.
Since Johne and Fronthingham described paratuberculosis for first time in 1895, BJD has spread around the world and has become a very important disease on dairy farms due to the economic losses that it produces. Although diagnosed for many years, in more recent decades the impact of BJD on dairy production has been more recognized, particularly on high production farms.
A problem in controlling the disease is the low sensitivity of most of the diagnostic tests, with infected but sero-positive animals retained leading to a failure to eliminate sources of infection. As vaccination in cattle is currently forbidden in Spain (note that vaccination of sheep is possible under special permission), the main control method involves management interventions. Addressing disease risk factors include: decreasing contact between healthy and infected animals; separating offspring from dams immediately after birth; using milk and colostrum from non infected cows; improving hygiene with attention to cleaning of feces to prevent the fecal-oral transmission; and raising replacement heifers in separate locations (Bastida and Juste, 2011). It should be noted that the best control of BJD is to reduce opportunities for transmission of the infectious microorganisms (Windsor and Whittington, 2010). Further, measures that increase animal welfare and reduce stress may also contribute to a lower incidence of the disease. Consideration should be given to encouraging farms with low incidence of the disease (around 5%) to use culling strategies to remove positive animals, previously based on ELISA tests but now preferably based on PCR of feces should the PCR be shown to have increased sensitivity.
BJD is a challenging disease for farmers and veterinarians and control measures must be implemented as soon as the disease is detected. In farms with high incidence of infection, in lieu of total de-stocking, a vaccination program would be a preferred strategy should it be permitted. Currently, in Spain, vaccination in only possible in that farms that are in a research project on BJD and with a special permission.