Epidemiology and Risk Factors of Infectious Bursal Disease: A Review

Review Article

J Bacteriol Mycol. 2024; 11 (2): 1219.

Epidemiology and Risk Factors of Infectious Bursal Disease: A Review

Abay Beshah¹; Abdi Ahmed²*; Morka Dandecha¹

1Ambo University, Department of Veterinary Laboratory Technology, Ethiopia

2Animal Health Institute (AHI), Microbiology Research Laboratory, Ethiopia

*Corresponding author: Abdi Ahmed Animal Health Institute (AHI), Microbiology Research Laboratory, P.O. Box 04, Sebeta, Ethiopia. Email: [email protected]

Received: April 02, 2024 Accepted: May 10, 2024 Published: May 17, 2024

Abstract

Infectious Bursal Disease (IBD) has been a great challenge to the poultry industry world-wide for a long time and has a major setback to productivity and profitability in the poultry industries of developing nations including Ethiopia. In Ethiopia IBDV was spread to almost all the regions and agro-ecological zones and a recent country wide study reported IBDV seropositivity rates in backyard chickens to be close to 95.7%. The infectious bursal disease is widespread viral diseases that affect chicken kept in commercial and backyard production system. Infectious bursal disease virus is a primary affect bursa fabricius of young chicks at the age of 3 to 6 weeks. The most common mode of infection is through the oral route, but conjunctiva and respiratory routes may also be involved. The infectious bursal disease is host-specific and extremely contagious. Age, breed, degree of passive immunity, the virulence of the strain of the virus, biosecurity, and secondary infections associated with the immunosuppressive effects are the most affecting risk factors of this disease worldwide. Although, many studies have been done as world and in Ethiopia concerning the prevalence and identifying predisposing factors of this disease, further experiment on developing vaccines of specific strains and implementation of prevention and control program are needed to be emphasized.

Keywords: Chicks; Epidemiology; Infectious bursal disease virus; Risk factors

Abbreviations: BF: Bursa of Fabricius; CSA: Central Statistical Agency; dsRNA: Double Stranded RNA; DXV: Drosophila X Virus; IBD: Infectious Bursal Disease; IBDV: Infectious Bursal Disease Virus; IPNV: Infectious pancreatic Necrosis Virus; MDA: Maternally Derived Antibody; NAHDIC: National Animal Health Diagnosis and Investigation Center; NCD: Newcastle Diseases; Nm: Nano Meter; OIE: Office of International Des Epizooties; PI: Post Inoculation; SPF: Specific-Pathogen-Free; USA: United State of America; Vv: Very Virulent; vv IBD: Very Virulent Infectious Bursal Disease

Introduction

The poultry sector is one of the segments of livestock sector in Ethiopia which can be characterized into three major production systems: large commercial, small scale commercial and village or backyard poultry production system. These production systems have their own specific chicken breeds, inputs and production properties. Each can sustainability coexist and contribute to solve the socioeconomic problems of different target societies [73]. Ethiopia has 60.51 million chickens population from which 94.33% of the chicken populations are indigenous chickens, while the remaining 3.21% and 2.47% consists of exotic and hybrid breeds [11]. They play a role by providing the needed animal protein that contributes to the improvement of the nutritional status of the people [77].

Ethiopian poultry production has a long traditional practice which is characterized by low input and low output [51]. This indigenous poultry production contributes 98.5 and 99.2% of the national egg and poultry meat production, respectively [73]. Chickens are especially important to women, children and aged individuals, who are the most vulnerable member of the society in terms of under nutrition and poverty; contribute a significant role in supplying animal origin protein to improve human nutrition [27]. Despite, Ethiopia owned huge chicken flock; there are different constraints like poor nutrition, poor management and prevalent diseases that hinder the productivity of the chicken in most area of the country [16].

Among the above obstacles, poultry diseases are the main constraints incriminated for reduction of total numbers and compromised productivity [5]. Among those diseases, Infectious bursal disease is the one that become a serious threat to cause frequent outbreaks and a challenge to the young growing poultry farms [72]. Infectious Bursal Disease Virus (IBDV) is the aetiological agent of Infectious Bursal Disease (IBD), also known as infections bursitis or avian nephrosis. It is a highly contagious disease of young chickens, usually between three and six weeks of age, characterized by high morbidity and mortality [17]. IBD is belongs to the Birnaviridae family and has a non-enveloped, bi-segmented, double-stranded RNA genome which contains a single-shelled, icosahedral capsid structured and having a diameter of 58 nm -60 nm. This relatively simple structure renders the virus very resistant to the outside environment [35]. Infectious bursal disease virus replicates in differentiating lymphocytes of the Bursa of Fabricius, causing the immunosuppressive and often fatal condition called Infectious Bursal Disease (IBD) or Gumboro. IBDV consists of two serotypes (Serotype 1 and 2). Only serotype I viruses are naturally pathogenic to chickens whereas serotype 2 virus apathogenic for chicks [33] and are classified as avirulent, classical, variant and very virulent (vv) strains [50].

The disease is characterized with a typical clinical sign of those an acute immunodepression, with depression, prostration of the affected birds, diarrhoea, during the first weeks of life. It is transmitted through orally via contaminated feed and water [69].

Infectious bursal disease is a newly emerging disease of chicken in Ethiopia, which has been speculated to be introduced concurrent with increased number of commercial state and private poultry farms flourishing in the country [3]. The first report of IBD in Ethiopia was in 2005 involving 20–45 day old broiler and layer chickens from commercial farms [85].

IBD is a disease of worldwide importance due to the huge losses as a result of opportunistic infections encountered by poultry farmers. The disease is especially a problem in developing countries due to challenges, including, but not limited to lack of appropriate vaccines that would be effective against evolving strains of the virus [48]. There is the existence of large gaps in information of the Epidemiology and Risk factors on Infectious bursal disease among poultry farmers. Subsequently, IBD has become a priority problem in commercial and backyard poultry production system despite of distribution of disease occurs; regular vaccination practices and improved biosecurity measures. Therefore, the objective of this seminar paper is:

¾To review the Epidemiology and Risk factors of Infectious bursal disease.

Literature Review

Background

Infectious bursal disease is also known as Gumboro disease which is a highly contagious disease of young chicken (Gallus gallus domesticus) caused by Infectious Bursal Disease Virus (IBDV) which belongs to a genus AviBirnavirus [23], of family Birnaviridae [14] that causes disease and mortality in young chickens mainly 3–6-week-old in the worldwide distribution [41]. The disease is characterized by sudden of short course and extensive destruction of lymphocyte particularly in the bursa of fabricius, where B lymphocytes mature and differentiate [66]; however, IBD viral replication also occurs in other lymphoid structures including the spleen, thymus, harderian gland, and cecal tonsils [63]. Initially there was a misconception that the disease was caused by Infectious Bronchitis Virus (IBV); this was because of presence of similar gross changes in the kidneys [39]. However, in subsequent studies, the causative agent for IBD was isolated in embryonated eggs and the disease given the respective name [82].

The causal agent of the disease was first isolated in Gumboro, Delaware in United States of America (USA), and the disease was originally known as Gumboro disease. It is a viral infection, affecting the immune system of poultry, which is the name derived, even if the terms IBD (infectious bursitis) are more accurate descriptions [10]. In the year of 1960 and 1964, the disease observed in most part of the USA and become devastating disease in Europe in the years of 1962 to 1971 [24]. Infectious bursal diseases currently become an international issue, 95 % of the 65 countries that responded to a survey conducted by the [56] that announced the presence of infection [21]. Infectious bursal disease virus has recently been isolated from a sparrow in China suggesting that wild birds could act as carriers [82], including New Zealand which had been free of disease until 1993 [22] and recently the IBD is reported indifferent parts of Ethiopia [3]. The disease has spread to all investigated commercial farms and multiplication centers occurring at an average outbreak rate of 3-4 farms per year. The disease was encountered commonly in backyard poultry production systems as well [47].

Etiology

Infectious Bursal Disease (IBD) is an acute, highly contagious viral infection of young chickens that has lymphoid tissue as its primary target with a special predilection for the bursa of fabricius. It was first recognized as a specific disease entity by Cosgrove in 1962 and was referred to as “avian nephrosis” because of the extreme kidney damage found in birds that succumbed to infection. Since the first outbreaks occurred in the area of Gumboro, Delaware, “Gumboro disease” was a synonym for this disease and is still frequently used [10]. Infectious bursal disease virus, classified in AviBirnavirus genus under the family of viruses called Birnaviridae family, is the causative agent of Infectious bursal disease [47]. The family includes 3 genera: Aquabirnavirus whose type species is Infectious Pancreatic Necrosis Virus (IPNV), which infects fish, mollusks, and crustaceans; AviBirnaviruswhose type species is Infectious Bursal Disease Virus (IBDV), which infects birds; and Entomobirnavirus whose type species is Drosophila X Virus (DXV), which infects insects [14].

Infectious bursal disease virus particles are bisegmented, double stranded RNA (dsRNA) genomes, non-enveloped virions, which are packaged into single shelled with diameter of 60 to 70 nm [19]. It is replicates in differentiating lymphocytes of the Bursa of Fabricius, causing the immunosuppressive and often fatal condition called Infectious Bursal Disease (IBD) or Gumboro [50].

Two serotypes of the virus have been described; these are Serotype 1 IBDV strains, pathogenic to chickens [38], whereas serotype 2 strains are non-pathogenic [8]. Serotype 1 IBDV isolates comprise the variant, classical virulent and vvIBDV strains, which wide differ in their pathogenicity to chickens. Variant IBDVs do not cause mortality, whereas the classical strains cause up to 20% mortality [50]. Chickens, especially young chicks at the age of 3 to 6 weeks, are the selected hosts for the serotype I virus [43]. In the case of vvIBDV infection, the age susceptibility is extended which covers the entire growing period in broilers [31]. In addition, it was reported that chickens infected with IBDV at the age of 14 days suffered from greater bursal atrophy and had higher viral RNA copy numbers than those infected on the day of hatching [36].

Pathogenesis; Incubation Period and Clinical Signs

Pathogenesis is defined as the method used by the virus to cause injury to the host with mortality, disease or immunosuppression as a consequence. Chickens acquire IBDV infection orally or by inhalation. The virus is transferred from the gut to the other tissues by phagocytic cells like macrophages. In macrophages of the gut associated tissues, it could be detected as early as 4 hours after oral inoculation using immunofluorescence [50]. The virus then reaches the bursa of Fabricius via the blood where the most extensive virus replication occurs. By 13 hours Post Inoculation (PI) most follicles are positive for virus and by 16 hours PI a second and pronounced viremia occurs accompanied by secondary replication in other organs resulting in disease and death [79].

The incubation period is very short which range from 2 to 3 days. In acute cases, the chickens become tired, prostrated, dehydrated, suffered from watery diarrhea, and feathers are ruffled [54]. Mortality commences on the third day of infection, reaches a peak by day four, then drops rapidly, and the surviving chickens recover a state of apparent health after five to seven days. Moreover, a primary infection may also be in apparent when the viral strain is of low pathogenicity or if maternal antibodies are present [76].

The clinical signs of IBD vary considerably from one farm, region, country or even continent to another [79]. In acute form, birds are prostrated, debilitated, dehydrated, with water diarrhea and swollen vents stained with faeces. In birds below three weeks, the disease is asymptomatic, but birds have bursal atrophy with fibrotic or cystic follicles and lymphocytopaenia before six weeks and are usually susceptible to other infections that would be contained in immunocopetent birds (Figure 1) [54].