Editorial 68: Veterinary experiences in epizootic diseases
The increasing emergence of bacterial or viral infections, that soon acquire the characteristic of epidemic for poultry and pigs, created the concept of mass pathology, replacing the individualized pathology used until that moment.
The evolution of poultry and pig farming radically changed the problems that arose from the mid-twentieth century to the present. Nowadays, billions of animals are raised in large communities in expressly built facilities. The increasing emergence of bacterial or viral infections, that soon acquire the characteristic of epidemic for poultry and pigs, created the concept of mass pathology, replacing the individualized pathology used until that moment.
In this situation veterinary pathologists were forced to develop answers to the many unknows that were presented:
When should I give importance to a pathological process? How can the cause-effect relationship of the suspected agents identified be confirmed? What is the influence of breeding conditions such as concentration of animals per m2 or per m3 of air, access to food or water? What is the influence of the origin of the animals and mixtures of animals of different origin? Is there any seasonal influence? Are farms located on migration routes of birds or other wildlife animals more exposed to infectious diseases?
In such circumstances, the criteria established by William Farr and Robert Koch and the research carried out by veterinarian experts in community pathology allowed to answer the initial questions:
William Farr (November 30, 1807 to April 14, 1883) established that daily mortality rate is the main criteria to consider the dangerousness of a process that is being observed. In addition, autopsies to identify internal lesions that correspond to the process must be done. For Farr, other less important parameters to consider were the daily contagion and positivity rates.
A few years later, Robert Koch (December 11, 1843 to May 27, 1910) took another step forward. Once Farr established the two main criteria (mortality and necropsy findings), Koch performed bacterial isolates. However, for Koch it was not enough to isolate a microbe in the lesions to consider the cause of it. For this reason, in 1884, he formulated a criterion designed to link the presence of a microbe with clinical specific lesion as its origin. These criteria were known from 1890 as Koch’s postulates. In essence, they are based on isolating a microbe from a patient, injecting it into a guinea pig, causing the disease and isolating the same microbe (and only this one) that was isolated from the first patient from the guinea pig.
This way, clinical veterinarians consider that the main criteria to establish whether it is a mass pathology or not are:
- Percentage of daily mortality greater than 0,01% of the population for two days (that is, 100 deaths per million individuals)
- Findings of specific lesions during autopsy
- Isolation of specific infectious agents in specific lesions
- Confirmation of the pathogenicity of the infectious agent
In clinical veterinary medicine, it is considered that if daily mortality is above 0.01% for 2 days, there should be an intervention. The first intervention is to perform necropsies of all the deceased animals and of some animals in critical condition. The second intervention is to obtain samples to send to the laboratory for analysis and confirm the pathogenicity of the isolated microorganisms.
From here, clinical veterinarians must find out the origin of the microorganism (food, drinking water, facilities, equipment, migratory routes, vertical infections, coexistence of birds of different ages …) and its sensitivity to chemotherapy accompanied by symptomatic drugs.
When the first phase of the intervention is completed, there is more time to prevent future infections, establish reliable tests, improve facilities and, if necessary, establish a vaccination plans base, primarily, on inactivated vaccines and without adjuvants that provide immunity without the possibility of adverse reactions.
Due to the industrial farming changes in recent years, it is important to follow the processes defined here to establish the danger of a pathological process. The observation and analysis of all the points will give us the keys to treat infections in the most appropriate way possible.
At VeterinariaDigital we claim the experience acquired by clinical veterinarians specialized in community pathology to deal with avian and pig epidemics that occur cyclically. As happened with Avian Influenza and Swine Influenza (both diseases seriously affected poultry and pig communities and nowadays their impact is minimal) or as is now happening with the African Swine Fever.