Perspective on Mycoplasmosis

by W.H. Wohler, DVM
It is not uncommon in cattle circles to hear the name Mycoplasma spoken as a new dreaded disease. Frequently one also hears about alleged strains of Mycoplasma that are presumed necessary to incorporate in so-called autogenous or custom vaccine in order to protect cattle against this mysterious new killer of stocker and feeder cattle. If one listens carefully it may even be heard that the problem is really BVD, and that if BVD were to be controlled, or eliminated Mycoplasmosis would disappear.
The facts are:

1. There is no obligatory relationship between Bovine Mycoplasmosis and BVD infection. Certainly if the two very immunosuppressive diseases occur concurrently in a herd of cattle, the problem will be greater than if either one occurred by itself. Mycoplasma bovis is quite competent to cause disease by itself without any other intercurrent disease. However, as with other infections, BVD makes cattle more susceptible to Mycoplasma bovis; there is more than a little suggestion that this may also be true for BVD vaccines. Mycoplasmosis in cattle is manifest as pneumonia, arthritis, ear infection, unthriftiness and poor performance.

2. Mycoplasma are the smallest free-living self-reproducing bacteria known to man. According to Quinn & Mackey, there are more than nine species of Mycoplasma that are associated with cattle. Two are of major economic significance, Mycoplasma mycoides and Mycoplasma bovis; the remainder are of minor or even questionable importance. Mycoplasma mycoides can be called the type specie. It is the most pathogenic of the lot and causes Chronic Bovine Pleuro Pneumonia (CBPP) which is an O.I.E. (Office of International Epizootics) “List A” disease and can be considered a potential terrorist agent. CBPP was eliminated from the U.S. in the 1890s and from Australia in the 1950s, it is thought to still exist in parts of Africa, the Middle East and Asia.

3. Mycoplasma bovis is credited with being the second most pathogenic species of Mycoplasma for cattle after Mycoplasma mycoides. Distribution is worldwide. It was first recognized in the U.S. in the 1960’s. Initial reports were of dairy cows with mastitis and dairy calves with pneumonia, arthritis and ear infections. In recent years it has become a major problem in stocker and feeder cattle both in the U.S. and Canada. Mycoplasma bovis is believed responsible for twenty five percent or more of bovine respiratory disease in the U.K.

4. There are several other species of Mycoplasma associated with cattle that are of lesser economic importance, Mycoplasma dispar has been reported to cause pneumonia in dairy calves and alkalescens and californicum as causing mastitis in diary cows; their importance in stocker and feeder cattle is unknown at this time. There are other species of Mycoplasma that have been isolated from cattle that are of minor or no economic importance. Accordingly, the importance of proper and complete identification of Mycoplasma isolates can not be understated. Identification of Mycoplasma is generally done by means of monoclonal antibodies or PCR. Monoclonal antibody techniques can be overly specific and not recognize some members of a specie, and PCR procedures can lead one to the conclusion that there are innumerable “strains” of any given specie of Mycoplasma. At this time there are NO proven sub species to exist, nor are there any known to exist variant immuno-protective strains of Mycoplasma bovis, and there is no scientifically established need to use multiple isolates (the term strain is often loosely applied) in the preparation of a vaccine. There are firms and individuals who have seized upon the PCR variability of Mycoplasma bovis to justify (and market) autogenous products. There is at this time no proven immuno-protective difference between isolates of Mycoplasma bovis but there are huge differences between autogenous and full license veterinary biologics.

5. Federal laws and regulations require that manufactures of a fully license product prove that their product is safe in the host animal (the species and class of animal it is to be used in), effective, potent and pure. In the case of an autogenous product, host safety, efficacy (effectiveness) and potency are not required to be proven – autogenous products are only required to be safe in eight lab animals (mice or hamsters) and sterile. The burden of responsibility for host safety, effectiveness and potency lies with the prescribing veterinarian and his client, a fact that should not be over-looked by feedlot managers and custom pasture operators.

6. Autogenous products do have a place. Should an aberrant immuno-protective strain that is clearly and scientifically shown to be not protected against by a full license product be recognized and/or an additional species to be found to cause economically important disease, it would then be appropriate to produce an autogenous product in order to meet the existing emergency situation. This is allowable by and is the intent of the Virus Serum Toxin Act, to allow the production of an autogenous product until such time as a full license product is available. In addition to the problems described above, antigen interference between Mycoplasma bovis and some other bovine pathogens is more than theoretical – it is a real issue. Some antigens are incompatible with others when fabricated into a vaccine. Without efficacy testing (which is not required for autogenous license products) such incompatibilities, may go unrecognized. Furthermore some vaccines interfere with the effectiveness of other vaccines when given separately but simultaneously or too close together, time-wise.

7. Mycoplasmosis in cattle is a disease that is not easy to understand and is difficult to immunize against. Considering all aspects of this complex problem, the best approach to management, control and prevention of Mycoplasmosis in stocker and feeder calves is to take all steps possible to mitigate against stress and maximize vaccination efficiency by using multiple does of a Full license product in an appropriate vaccination regime. Early recognition and aggressive therapy are essential to the successful treatment of clinical cases. Vaccination will not prevent all cases but vaccinated cattle that do develop the disease tend to respond better to proper treatment than non-vaccinated cattle. ©