In small ruminants it is not necessary to generate interest in this process among the technicians, considering the importance of these disorders, though we believe it is necessary to stress that in many cases agalactia manifests a chronic process indistinguishable from subclinical or chronic mastitis.
Agalactia is clinically characterized by three symptoms (mammary, articular and ocular). However, two different situations can be described: one in which the whole herd is affected, with intense manifestations, and another presentation in which sporadic clinical cases alternate with silent periods. The former presentation usually coincides with primary outbreaks, while the latter is found in chronically affected herds. In these animals with chronic processes, the appearance of stressing situations induces the development of clinical episodes.
The carrier animals play a preponderant role in maintaining infection in the herd, and in introducing it to others. In fact, when we introduce a batch of animals to the herd we can trigger the clinical process in the new animals if the old ones are already infected; alternatively, the old animals can be infected by the new batch if the latter carry the disease. As was already mentioned in the case of bovine cattle, a good approach may be to collect a tank sample on the farm from which the animals originate, and perform tests to identify Mycoplasmas. The destination farm must of course also be evaluated.
In goats, attention has also been drawn to the importance of the auricular Mycoplasma carrier as a relevant factor in the introduction of the disease. It also seems that certain acarid species found in the external auditory canal may contain high levels of these microorganisms.
Although vertical transmission has not been demonstrated, it is clear that Mycoplasmas are transmitted to the newborn animal through the milk and colostrum; as a result, under no circumstances should the offspring of animals that have undergone agalactia be maintained. Contagion among animals fundamentally involves horizontal transmission, and clearly in milk- producing animals, milking is an ideal moment. In fact, all secretions can serve as vehicles for Mycoplasma (milk, mucus, feces, urine, vaginal secretions, etc.). Moreover, Mycoplasmas appear to be able to spread through the air and persist in feces and soil — as a result of which communal pastures are obviously a place of risk.
The symptoms involve a sudden drop in milk production, as well as milk alterations. The affected animals also tend to present auditory and eye problems. In contrast, the chronic presentations evolve for years with no symptoms other than a reduction in milk production and progressive atrophy of the mammary glands that ultimately leads to removal of the animals. It should be taken into account that in some cases the process is accompanied by respiratory symptoms.
WHEN TO SUSPECT AGALACTIA
Agalactia should be suspected when new animals have been introduced to the herd and we observe some of the known symptoms of the disease. The condition may likewise be suspected when microbiological diagnoses of mastitis are made and the tests prove negative. In this sense, the microbiological findings are negative because Mycoplasmas are slow-growing microorganisms (up to 10 days) and require special conditions that are not used in routine diagnostic procedures.
WHAT SAMPLES TO COLLECT
- Milk samples. Disinfect the teat with 70% alcohol. Discard the first two milk streams and collect the third in a narrow-lipped tube (e.g., Venojet). Shipment can be made without having to refrigerate the sample.
- Swab sampling of the conjunctiva (when symptoms appear). The swab should be passed gently over the conjunctiva. It should be remembered that swabs with maintenance medium are required here.
- Joint fluid samples. These are to be collected with a sterile needle, introducing the samples in Venojet tubes.
CONTROL OF THE PROCESS
Antibiotic treatment is scantly effective, due to the appearance of resistance, the difficulties involved in securing sufficiently high drug concentrations in those places where the pathogen is found, and the fact that Mycoplasmas lack a wall — and are therefore insensitive to antibiotics that act at this level (e.g., the penicillins). In fact, the administration of antibiotics can actually worsen the situation, since by eliminating other pathogens the spread of Mycoplasmas is facilitated. In any case, treatment in the form of macrolides and quinolones appears to be the indicated approach.
As we have already mentioned, the best measure is to ensure adequate control of the animals introduced to the herd. However, when the herd is already chronically ill, an alternative approach is required.
Control of Mycoplasmas:
- Minimize vertical transmission by using artificial colostrum. In this sense, artificial or pasteurized colostrum limits infection by Mycoplasmas, Maedi Visna CAE, Coxiella, etc. Artificial lactation in turn reduces the problems posed by ecthyma and even Staphylococci.
- As far as possible, the sharing of pastures or common spaces with other herds should be avoided.
- Maximum milking hygiene is recommended to avoid horizontal contagion.
- To our knowledge, no intramammary agent has been developed to date capable of offering efficacy against Mycoplasmas. Consequently, intramammary drying can be complemented with intramuscular therapy using some product of established activity against Mycoplasmas. Some veterinarians even advocate the substitution of intramammary drying with intramuscular treatment. For several reasons, it is important to avoid the appearance of complications due to fungal species as a result of poor manipulation in drying, thereby contributing to reduce the costs and facilitate the application of treatment. In fact, intramammary treatments can be obviated in animals without subclinical mastitis at the time of drying.
Drying treatment via the intramuscular route has been used with some products that have been shown to offer efficacy against Staphylococci.
- It is advisable to vaccinate all the animals in order to avoid the appearance of Mycoplasmas. In this context, autovaccines offer the advantage of being prepared with the microorganisms isolated on the affected farm.
NOTE: In no case should Mycoplasma control be limited to the use of autovaccines.
NOTE: Exopol is the leading company of a European project (EUREKA) for the study of Mycoplasmas and the preparation of corresponding autovaccines using liposomes and exopolysaccharides.
We recommend the following vaccination protocol:
- Vaccinate and revaccinate the females with an interval of 21 days. The second dose should be administered 15 days before delivery.
- Use a reminder dose at each lactation. The young females should be vaccinated and revaccinated with an interval of 21 days.
MYCOPLASMA-INDUCED MASTITIS IN BOVINE CATTLE
Mycoplasma-induced mastitis has traditionally been associated with severe clinical processes, and moreover the cause of appearance of the disease was considered to be the introduction of some carrier animal to the farm. However, this is not entirely true. In fact, not only are Mycoplasmas isolated from milk in the absence of clinical manifestations, but they are also identified on farms where new animals have not been introduced for many years. The present circular will briefly discuss some of these aspects.
WHEN TO SUSPECT
With some frequency, the microbiological tests of samples of clinical or subclinical mastitis yield negative results. In some of these cases we can suspect the presence of Mycoplasmas, though caution is required since negative samples very often also appear in mastitis produced by coliform and environmental species in general.
As an example, in summer it is common to see that the animals that have been put to pasture concentrate in the corner where the manure is accumulated, or in the more humid zones — thus producing an increase in the prevalence of mastitis due to enterobacteria, many of which yield negative microbiological results.
When negative microbiological readings are repeatedly observed in subclinical or clinical processes, the implication of Mycoplasmas is a possibility to be taken into account.
In this sense, the microbiological findings are negative because Mycoplasmas are slow-growing microorganisms (up to 10 days) and require special conditions and media that are not used in routine diagnostic procedures.
On the other hand, the recent introduction of new animals to the farm is also a reason for suspecting Mycoplasmas, though such introduction is not absolutely necessary. In fact, the Mycoplasmas that most often produce mastitis in dairy cattle can be found in other zones within the cow (respiratory tract, urogenital apparatus, joints). Any stressing situation such as delivery, extreme temperature variations, other diseases, traumatisms, etc., can favor penetration of the microorganism to other tissues, including the mammary glands. Based on these considerations, it is easy to understand how any animal could be an asymptomatic carrier.
The clinical picture is suspected by the existence of various affected glands in the same animal, milk alterations and a sudden drop in production. However, many variations in these symptoms have been described. In fact, some farms show no such manifestations. On the other hand, it should be taken into account that in some cases and in periods that can range from a few days to several months before the detection of clinical mastitis, respiratory disorders may already be apparent.
Mycoplasmas are generally introduced to a given herd by animals coming from outside. In turn, most infections are transmitted during milking, or in intramammary treatment - though horizontal airborne transmission is also possible. For example, we are presently working with an infected farm where the source of the disease is suspected to be an adjacent-lying feeding place.
It has also been postulated that infected semen can transmit the disease — an idea that would explain some of the problems found on large farms, where the introduction of animals as a source of infection is discarded. Finally, Mycoplasmas can be transmitted to calves via the urogenital tract or through the milk of infected animals. For this reason it is important not to retain calves of animals that have suffered the process.
There is no effective treatment for Mycoplasma-induced mastitis. The control of the disease is based on identification of the infected cows by means of the bacteriological culture of samples of milk from all the cows. The culturing of tank samples is also recommended, to control the absence of the pathogen on the farm. Once identified, the infected animals must be separated from the herd and are to be milked last, until they finally leave the farm. Many animals can undergo chronic transformation and excrete bacteria in milk on an intermittent basis. Consequently, if the number of infected animals is small, the most reasonable approach is to eliminate them.
Use tank samples to test for Mycoplasmas.
If any of your clients plan to purchase animals from some other farm, the cattle should be placed under quarantine before introduction to the herd, and should be evaluated for Mycoplasmas in milk. This may be quite difficult in certain cases, particularly when calves are involved. We suggest the collection of various tank samples from the farm of origin (if possible), analyzing them to determine the absence of Mycoplasmas. It must be remembered that this study should be done several times.
The tank receives the milk from all the animals on the farm; it is therefore very useful for determining the possible presence of different pathogens, using specific growth media. On the other hand, it should be taken into account that the pooling of milk in the tank dilutes any pathogens that may be present; thus, even though the observed concentrations may be very low, it is still possible that their presence is not an isolated finding. For this reason the importance of tank studies increases greatly when such evaluations are made on a periodic basis, for example 2-4 times a year.
WHAT ARE MYCOPLASMAS?
Mycoplasmas are the smallest free-living organisms known. They only contain the minimum organelles and metabolic machinery required for growth and cell replication. In this sense, Mycoplasmas are reduced to the cell membrane, ribosomes and DNA, and lack a cell wall. This is an important characteristic in relation to treatment. On the other hand, it is precisely this simplicity that makes them expensive to diagnose. The limited genetic information contained within Mycoplasma cells does not include the capacity to produce cholesterol; consequently, the latter must be added to the growth medium in the form of extremely expensive sterile horse serum.
As we have already mentioned, Mycoplasma infections cannot be successfully treated with antibiotics. The reasons are varied, and include the limited capacity of antibiotics to penetrate to the areas where Mycoplasmas are located (joints, eye, ganglia, etc.). On the other hand, since the cells lack a wall structure, all antibiotics that act upon the bacterial wall (e.g., the penicillins) are totally ineffective in combating Mycoplasmas. Indeed, antibiotic treatment may be deleterious, since by eliminating other mammary pathogens, the colonization of mammary tissues by Mycoplasma is made easier.