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| Livestock Research for Rural Development 21 (12) 2009 | Guide for preparation of papers | LRRD News | Citation of this paper |
A study was conducted to determine the incidence of infectious bursal disease in chickens owned by 775 households in two districts of Amhara Region, Northwest Ethiopia from November 2007 to April 2008. Clinical, pathological and serological studies were conducted to confirm IBD as outbreaks in the study areas.
During the study period, the incidence of IBD was found 38.39% in Bahir Dar and 17.40 % in Farta. The case fatality rates were 98.56% in Bahir Dar and 77.73% in Farta. There was significant difference (p£0.05) in the incidence and case fatality rates of IBD among the study districts. Chickens in the households of Bahir Dar district was found 1.69 (OR=1.69) times more likely to be affected by IBD than those in Farta district. Birds with a clinical signs of vent picking and diarrhea had gross and microscopic lesions suggestive of IBD. Agar gel immunodiffusion test revealed the presence of antibodies against IBD in the serum of most recovered birds from IBD. This is the first report of IBD in village chickens in Ethiopia. Thus, it is of paramount importance to design cost effective control methods against IBD in order to improve the productivity and welfare of village chickens and also to conserve the indigenous chicken genetic resource.
Key words: IBD, indigenous chickens, Newcastle disease, poultry, villages, viral diseases
Chicken production under backyard system has long been practiced in Ethiopia. Village chickens have been widely used for egg and meat production, and also they serve other purposes (Alemu 1995; Tadelle and Ogle 2001; Halima et al 2007). Even though, village chicken products are the main and often the only sources of animal protein for poor households (Horst 1989); they are poor in productivity.
Constraints which could restrict the potentiality of village chickens in Ethiopia include low inputs of feeding, poor management, infectious diseases and lack of appropriate selection and breeding practices (Alemu 1995; Tadelle and Ogle 2001; Halima et al 2007). In recent years, however, attempts are underway to enhance chicken productivity and their contribution via importing exotic chickens and also by crossbreeding and distributing improved breeds to poor farmers living in the rural part of Ethiopia. However, infectious diseases are becoming real threats to chicken production (Alamargot 1987; Zeleke et al 2005a). The distribution of improved breed of chickens from infected poultry breeding and multiplication centers to the village is suspected of disseminating diseases to indigenous chickens reared by the poor farmers. Viral diseases such as Newcastle disease (ND) and infectious bursal disease (IBD) are reported to be the major health constraints of chickens reared in commercial poultry farms and in breeding and multiplication centers (Alamargot 1987; Alemu 1995; Zeleke et al 2005 a and b). However, the real impacts of infectious diseases in village chickens are not thoroughly investigated in most parts of Ethiopia. Recently, the occurrence of infectious bursal disease in some parts of the country have wiped out large number of chickens in private commercial poultry farms and in government owned poultry Farms (Zeleke et al 2005a; Woldemariam and Wossene 2007).
Infectious bursal disease (IBD) is an acute and highly contagious viral disease of young chickens caused by infectious bursal disease virus (IBDV), which belongs to the genus Avibirnavirus of the family Birnaviridae. Highly pathogenic strains of IBDV are known to cause 10-100% morbidity and mortality of 20%-50% (Chettle et al 1989). There is no report on infectious bursal disease from village chickens in Ethiopia. Thus, the objective of the study was to determine the incidence of IBD in village chickens raised under the backyard production system.
The study was conducted in two Bahir Dar and Farta districts, which were considered as a model in the Amhara region, northwest Ethiopia for launching poultry production extension packages by the government through distributing improved day old chicks to the farmers. Bahir Dar district is located in the Northwest part of Ethiopia at about 578 kms from the capital city, Addis Ababa. Bahir Dar district has an altitude range of 1730-2300 masl. The district has mid-altitude agro-climatic zone, with an annual rainfall of 800 to 1250 mm. The mean annual minimum and maximum temperature is about 10 and 32°C, respectively. Farta district is also located in the Northwest part of Ethiopia at about 676 kms from Addis Ababa with an altitude range of 1920 to 4135 masl. This area has a highland agro-climatic zone, with annual rainfall of 1250 to 1599 mm. The mean annual minimum and maximum temperature was 9.9 and 21°C, respectively (BoARD 2003).
The birds village chickens of 775 households (n=392 from Bahir Dar and n=383 from Farta) were purposively selected and observed twice a week and were closely observed, for six months (i.e., from beginning of November 2007 to end of April 2008) and sick birds were isolated and the clinical signs manifested were recorded and followed separately until they recovered or died. All those birds died during the working days were examined following the standard postmortem procedures.
Accordingly, disease diagnosis was made on the basis of history, clinical signs manifested and postmortem lesions. Acutely sick birds and/or recently dead ones were subjected to clinical inspection and as well as to postmortem examination to observe clinical signs and/or macroscopic lesions suggestive of IBD. At necropsy, bursae and spleen were examined and 4-6 mm thick tissues were collected and preserved in 10% neutral buffered formalin for 48 hours for histopathology.
Tissues were then processed (dehydrated, cleared, impregnated and embedded), sectioned (4 mm thick) and stained with hematoxylin-eosin according to the protocol provided by Bancroft and Harry (1994) and examined histopathologically to evaluate bursal and splenic lesions.
Blood samples (2-3 mL) were collected from the brachial vein of sick chickens using plain vacutainer tubes and with 18-20 gauge hypodermic needles. The tubes were labeled and set tilted overnight at room temperature to allow clotting. Then serum samples were isolated and kept in vials and stored at -20ºC until Agar gel immunodiffusion test was performed. Infectious bursal disease specific antibodies were detected using Agar gel immunodiffusion test. Antigen containing infectious bursal disease virus was prepared from bursal tissues collected from clinical cases of IBD. Bursal tissues were sliced and homogenized into 50% (w/v) suspension in phosphate buffered saline (PBS) containing 2% Triton (X100). The homogenate was centrifuged at 3000 rpm for 20 minutes and the supernatant was used as antigen (OIE 1996; Chuahan and Roy 1998). Five rounded wells 2 mm in diameter were cut 1 cm apart in a layer of agar on a petridish. The well at the center was filled with soluble antigen, the other three with test sera and the last well with known hyperimmune serum. In places where the antigens and antibodies meet in optimal concentration, an opaque white line of precipitate was observed in positive cases (OIE 1996).
Descriptive statistics was utilized to summarize data on incidence and case fatality rates. Chi-square test statistics was used to evaluate the incidence of IBD among the study sites. Tests were considered significant at p<0.05.
The total number of chickens at the beginning of the study period was 2593 in Bahir Dar and 1316 in Farta district. During the study period, the incidence of occurrence of IBD was 38.39% in Bahir Dar and 17.40 % in Farta. The case fatality rates were 98.56% in Bahir Dar and 77.73% in Farta. The occurrence of IBD was confirmed on the basis of Clinical signs, pathological and serological tests. Clinical signs of infectious bursal disease were observed in chicks of less than two months of age. These include vent picking, whitish/yellowish diarrhea, depression, inappetance and sudden death.
There was significant difference (p£0.05) in the incidence and case fatality rates of IBD in the two districts. Those chickens in the households of Bahir Dar district was found 1.69 (OR=1.69) times more likely to be attacked by IBD than those in Farta district.
During the six months study period, the incidence of IBD in Bahir Dar district in chickens revealed four patterns. In the first pattern the incidence was declining from November to December. Afterwards, the incidence of IBD was increasing and the peak was recorded in January. The third pattern was from January to March showing a dramatic fall. At last, the incidence rate was increasing as of March to April. However, the incidence rate in Farta showed gradual increase from November to April (Figure 1).
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In Bahir Dar as the incidence rate of IBD increases, the case fatality rate decreases. This may be related with the development active or passive immunity against IBD. However, in Farta, the case fatality rate increases for sometimes and started declining even when the incidence rate increases (Figure 2).
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At postmortem examination, ecchymotic hemorrhages were observed on the thigh and breast muscles(Figure 3a) and at the proventriculus-gizzard junction(Figure 3b). The bursa of Fabricius was hyperemic and enlarged and when opened (Figure 3c and d), the bursa was filled with necrotic yellowish debris(Figure 3e).
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Histopathological evidences of infectious bursal disease were detected in the bursae and spleen. The prominent bursal lesions include hemorrhagic lesions in the interfollicular space, heterophilic infiltration in the follicles with necrotic centers, follicular atrophy, lymphoid cell depletion and the formation of cystic cavity in the medulla(Figure 4 A,B,C and D).
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B. Cystic cavity in the medulla of the bursal follicles (100x) C. Heterophilic infiltration in the bursal follicles (400x) D. Bursal follicles with necrotic centers (1000x) |
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The spleen of affected chickens was also enlarged. Similar necrotic process has been observed in the white pulp of the spleen (Figure 5A, B, and C and D).
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The present study discloses infectious bursal disease (IBD) as being one of the most important viral diseases of chickens in the study sites. The cumulative incidence of IBD was calculated at 38.39% in Bahir Dar and 17.40 % in Farta. The case fatality rates of IBD were 98.56% in Bahir Dar and 77.73% in Farta districts. Clinical, pathological and serological studies revealed IBD as the most common causes of deaths in large proportion of chickens in the study sites.
Episodes of infectious bursal disease outbreaks in several commercial poultry farms and poultry breeding and multiplication centers have wiped out large number of exotic chickens. Over the past few years, 25 to 75% of the deaths/losses in exotic and cross chickens have been associated with infectious bursal disease (Zeleke et al 2002; Zeleke et al 2005a; Woldemariam and Wossene 2007). Highly pathogenic strains of IBDV are known to cause 10-100% morbidity and mortality of 20%-50% (Chettle et al 1989). Furthermore, in non-immuned and highly susceptible chicken flocks highly pathogenic strains of IBDV were reported to cause mortality exceeding 90% (Nunoya et al 1992). The reason for significant difference in incidence and case fatality rates of IBD between the study districts may be associated with the variation in age, number and type of chickens raised in the study sites. Histopathologically, IBD was confirmed with the characteristic bursal lesions consisting of lymphoid cell depletion and cystic cavity formation in the medulla of the bursal follicles. The depletion of B-cells in the spleen may indicate that the virus strains causing the disease may be highly pathogenic ones. In recent years, highly pathogenic (hotter) strains are emerging via mutation and genetic re-assortment (Mardassi et al 2004). Previously, highly pathogenic strains of IBDV, the cause of IBD, are known to cause B-cell depletion in the thymus and spleen (Corley et al 2001). Infectious bursal disease has a worldwide distribution whereby all poultry producing countries suffer from the immunosuppressive effects of the disease (Lukert and Saif 1997). IBD was also reported from other country in Africa (Kelly et al 1994). Considering the higher incidence and case fatality rates of IBD revealed by the present study it would be important to plan and execute an appropriate preventive and/or control strategies against the disease. Otherwise commercial poultry farms, poultry breeding and multiplication centers and the genetically important indigenous chickens may be regularly attacked with several outbreaks of IBD. In addition, the virus strains circulating in the country should be genotyped for vaccine formulation.
Infectious bursal disease is prevalent in the study districts and is known to cause heavy mortality and morbidity. It is considered as a newly appearing disease in many areas in Ethiopia.
Considering the relatively high incidence of IBD as revealed by the present study it would be important to plan and execute an appropriate preventive and/or control strategies against this viral disease. Otherwise commercial poultry farms, poultry breeding and multiplication centers and genetically indigenous local chickens may be regularly attacked with several outbreaks of IBD. Moreover, the poultry development schemes might not feasible if preventive measures are not instituted urgently.
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Received 10 May 2009; Accepted 19 August 2009; Published 3 December 2009
