Circulation of Immunosuppressive Viruses and Avian Encephalomyelitis Virus in Backyard Chicken Flocks

The objective of this study was to evaluate the circulation of Chicken Anemia Virus (CAV), Infectious Bursal Disease Virus (IBDV), Avian Reovirus (ARV) and Avian Encephalomyelitis virus (AEV) in properties of backyard chickens and carry out an epidemiological analysis. We evaluated 200 samples of chickens from 19 backyard chicken property. Only one property (P10) did not present serological titers for the diseases evaluated. This property is close to industrial farms as well as the other properties, however, P10 remained a few years without the breeding of chicks and these were the first poultry to be housed on site. This reinforces the importance of the fallow period for poultry production. The prevalence of virus-seroreactive birds was 78% (156/200), 64.5% (129/200), 78% (156/200), 78% (156/200) for CAV, IBDV, ARV and, EA, respectively. All the free-range farms studied are within a radius of 500 meters to 6 Km away from some establishments of industrial poultry. There was a correlation between serological titers for CAV and the frequency of disease in poultry (r = 0.6178). In places where birds are frequently sick, 30.76% reported that the disease occurs in chicks, 30.76% in broilers, 23.07% in broiler chickens and 7.69% in birds of all ages. Birds get sick more often in the summer period. The owners reported that the most common signs of disease were respiratory signs (snoring and nasal discharge) (46.15%), diarrhea (30.76%), and paralysis of wings and/or paws (38.46%). There was a correlation between the presence of untreated water in the property and serological titers for ARV (r = 0.5576). This report draws attention not only to high serological prevalence for the viruses studied but also important epidemioHow to cite this paper: Almeida, P.C., Borges, P.R.S., Koerich, P.K., Melo, R.T., Batista, I.A., Mendonça, E.P., Silva, R.R., Silva, L.K. and Fonseca, B.B. (2020) Circulation of Immunosuppressive Viruses and Avian Encephalomyelitis Virus in Backyard Chicken Flocks. Advances in Microbiology, 10, 203-213. https://doi.org/10.4236/aim.2020.105016 Received: November 29, 2019 Accepted: May 3, 2020 Published: May 6, 2020 Copyright © 2020 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/


Introduction
Brazil is recognized worldwide for its excellence in industrial poultry farming, highlighting its technology in management, standardization in production respecting animal welfare, traceability and biosecurity. These characteristics are associated with industrial production although the practice of poor creation technology is a reality relevant to the country.
The creation of backyard chickens has been widely exploited over the years by small producers. Many of these breeding farms do not have specialized consulting to obtain adequate management yet; and due to the lack of information on basic biosecurity, they have low sanitary status and may result in the emergence of diseases. Properties with low sanitary status represent a risk for industrial poultry farming, mainly where there is intense exploitation of poultry such as in the south and southeast regions of the Brazil.
Immunosuppressive diseases are of great importance in poultry production.
These make them susceptible to various other illnesses, which include zoonotic diseases, especially those transmitted by food such as salmonellosis and campylobacteriosis. Some of these diseases are difficult to control, at the same time they can cause economic losses, due to the drop in production, and a high rate of morbidity and mortality [1]. Among the most important viruses that affect the immune system of poultry, we can describe Chicken Anemia Virus (CAV), Infectious Bursal Disease Virus (IBDV), and Avian Reovirus (ARV). These viruses cause chicken infectious anemia (CIA), infectious bursal disease (IBD) and avian reoviruses (REO) respectively.
Caused by a DNA virus, from the Circoviridae family, CIA is evidenced by transient anemia, growth retardation, thymus hypoplasia, and other signs [2]. The IBD is caused by an RNA virus and can be present in the clinical or subclinical form [3]. Sudden or high mortality and drop in production are determinant factors of the economic impact of this disease. The Avian Reovirus (ARV) belongs to the genus Orthoreovirus, family Reoviridae being the disease commonly associated with other pathogens. Affecting the gastrointestinal tract, respiratory system, and skeletal tissue, REO mainly affects young birds [4]. Another disease of high relevance is avian encephalomyelitis (AE) caused by the Avian Encephalomyelitis virus (AEV). Infected breeding in the posture period transmits the disease via vertical, and the chicks will present nervous signs such as ataxia, tre-mors, paralysis, and death in a few days [5] [6] [7]. All the diseases presented here are resistant to the environment [8] [9] [10] [11].
Since the mentioned diseases are extremely relevant to poultry production, monitoring and control must be continuous. Also, despite the importance of the viruses that cause these diseases in industrial poultry, little is known about their interference in backyard chicken production. Thus, the objective of this study was to evaluate the prevalence of the CAV, IBDV, ARV and AEV in properties of backyard chickens and carry out an epidemiological analysis between the serological titles, clinical disease and some biosecurity factors.

Material and Methods
Blood samples from 200 backyard chickens aged between 12 and 56 weeks were  The free-range farms were evaluated as some points related to biosecurity and to the clinical signs of diseases. These were mapped relating proximity to the industrial farms of the region using Google Maps. For statistical analysis, the Kolmogorov-Smirnov test was used to verify whether the data were parametric for further analysis of the differences between averages by ANOVA. The correlation test performed was Pearson's test. A significance level of 0.05 was considered and the Graph Pad Prism 7.0 program was used.

Serologic titers evaluated
From the free range farms visited, there was previous vaccination in the properties P5 and P19 for IBDV. The farmers were not able to inform whether the same birds evaluated in this study had been vaccinated for the mentioned diseases. However, in these country farms there was a vaccination approximately 6 and 12 months before to the collection. The mean serologic titers of the evaluated country farms for the diseases that affect the immune system and AE are described in Figure 1.
According the manufacturer's guidance of the ELISA, title values above 397 are considered seropositive for IBDV, AEV and ARV and above 1000 are considered seropositive for CAV. Thus, when assessing the population mean, it is possible to notice that the properties P5, P10 and P14 were those that did not react to ARV; P8, P10, P15, P16, P18 did not react to IBDV; P10 did not react to AEV and CAV. The country farms P3, P14 and P15 were the most reacted to CAV; P8 and P12 for ARV; P14 and P19 for IBDV and P6 and P8 for AEV. The P10 was the only one that was not reagent for any of the viruses evaluated.
In addition to the evaluation of the mean serological titers, the histograms were constructed to better evaluate the serological titers in the free-range farms.
For this, the titles were divided into categories exactly as recommended by the  Figure 3). However, these free-range farms remained a few years without the breeding of birds, and these were the first birds to be housed on-site. The birds evaluated in this way had similar ages (approximately 16 months of age).   Disease evaluates and serological titers Table 1 presents the correlation test between the serological titers for the eva- There was no correlation between serological titles and characteristics of the farm, multispecies breeding, and cleaning of facilities. In free-range farms where there were multispecies breeding the most common birds were hens, ducks, and geese.

Discussion
In Brazil, the epidemiological status of backyard chickens is poorly studied and the prevalence of antibodies to IBDV, CAV, AEV, and ARV is not well known.
In the present study, IBDV presented a prevalence of 64.5% and 78% for CAV,

AEV or ARV. Titles values for IBDV were also high in backyard chicken in Rio
Grande do Sul (80.2%) [12] and Slovenia (78%) [13]. The serological prevalence for ARV was 21.6% in Rio Grande do Sul [12], 41% in Nigeria [14] and 92% in Slovenia [13]. The values found for AEV ranged from 57.1% in Sudan [15], 65% in Galapagos Island [16] and 82.23% in Lower Paraguaçu-Bahia [17]. It is not common to find report results of serological prevalence of CAV in backyard chicken.
Although some researches mention the high prevalence of virus evaluated in backyard chickens, it is not common to find reports of clinical disease in these poultry. As discussed by Barrios et al. [18], backyard chicken, in natural challenge selection, seems to be more resistant to clinical disease caused by CAV than industrial poultry. The Serological prevalence reported in our study indicates that the virus is circulating but leads to hypothesize that the pathogen, host and environment relationship can be determinant in the manifestation of these diseases in backyard poultry. It is probable that the low-density breeding with free access will determine the non-occurrence of the clinical disease when com- This shows the importance of fallowing to reduce the pressure of infection even related to viruses of difficult control as those researched in this report.
Lack of vaccination, stress due to coexistence with other birds, and dirty environment are predisposing factors to viral, bacterial or fungal infectious diseases [21]. However, in this study, we have not found a correlation between the cleaning conditions of the facilities. We should consider here a possible bias about our results since no property presented good classification for cleaning conditions.
Although the importance of multispecies creation for the increase of diseases is recognized, in this study, the presence of poultry of different species on the same property has not interfered with serological titers. For most of the diseases evaluated in this work, the natural host is the chicken, and perhaps, for this reason, the correlation between multispecies creation and the high serological title was not found. However, the presence of multispecies of birds in the same property can be considered an alert because of the possibility of mutation and genetic P. C. Almeida et al.
recombination of the agents facilitated by the interspecies dissemination.
In the correlation study, CAV showed a correlation with the parameter "poultry get sick frequently" with r = 0.6178. According Mukaka [22], a value of r between 0.5 and 0.7 indicates a moderate correlation. Farmers indicated for us that clinical signs were prevalent among young birds (chicks 23.07% and broilers-30.76%); hot period of the year (summer-69.23%) and associated with symptoms of snoring and nasal secretion (46.15%) followed by paralysis of wings and legs (38.46%) and diarrhea (30.46%). The present signs reported by the farmers are not indicative of either CAV or other diseases evaluated in this study.
The CIA is a disease of young birds, characterized by marked anemia, bone marrow hypotrophy, increased mortality, reduced weight gain, and generalized atrophy of lymphoid organs [23]. Beside this, disorders caused by CAV induce immunodepression [2] [24] [25], which increased susceptibility to other infections [26]. When we visited the farms, we observed that the main clinical symptoms were those related to the respiratory tract (mucus in the nostrils, swollen head and tearing). Prezotto et al. [26] verified synergic pathological effects of CAV and a respiratory microorganism (Mycoplasma gallispticum). Older birds are susceptible to viral replication but do not develop clinical signs [27]. Farmers reported that the disease occurs at the same ages that CAV is described-chicks and young chicken. Admittedly, it is important to mention, that our analysis may contain bias as poultry may have fallen ill at a different moment from the presence of serological titers. Thus, it is possible that the birds became ill due to IBDV, AEV or ARV before our serological analysis. However, we do not have this accurate information.
The summertime was reported as the most critical for disease manifestation.
In the region where poultry is raised, summer is a period associated with rain, where high temperature and humidity can favor the spread of numerous pathogens.
The presence of ARV titers in the present study showed a correlation with untreated water, probably explained to be a virus resistant to environmental conditions and disinfection [10].

Conclusion
This report draws attention not only to high serological prevalence for the viruses studied but also to epidemiological aspects important for diseases in backyard chicken who may indirectly influence birds in industrial production. The report reinforces that even in countryside areas the period of downtime decreases the infection pressure and also shows that the presence of CAV in the properties may predispose to other clinical diseases in birds. Surveillance for the virus assessed in this study should be constant in backyard chicken production since the proximity to industrial poultry production may lead to cross-contamination which may result in the appearance of strains with genetic alterations in the future.