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Poult Sci 2008. 87:444-448. doi:10.3382/ps.2007-00415
© 2008 Poultry Science Association
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IMMUNOLOGY, HEALTH, AND DISEASE: Research Note

Molecular Survey of Avian Respiratory Pathogens in Commercial Broiler Chicken Flocks with Respiratory Diseases in Jordan

D. A. Roussan1, R. Haddad and G. Khawaldeh

Provimi Jordan, PO Box 499, Amman 11118, Jordan

1 Corresponding author: droussan{at}provimi.com.jo


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Acute respiratory tract infections are of paramount importance in the poultry industry. Avian influenza virus (AIV), infectious bronchitis virus (IBV), Newcastle disease virus (NDV), avian pneumovirus (APV), and Mycoplasma gallisepticum (MG) have been recognized as the most important pathogens in poultry. In this study, trachea swabs from 115 commercial broiler chicken flocks that suffered from respiratory disease were tested for AIV subtype H9N2, IBV, NDV, and APV by using reverse transcription PCR and for MG by using PCR. The PCR and reverse transcription PCR results showed that 13 and 14.8% of these flocks were infected with NDV and IBV, respectively, whereas 5.2, 6.0, 9.6, 10.4, 11.3, and 15.7% of these flocks were infected with both NDV and MG; MG and APV; IBV and NDV; IBV and MG; NDV and AIV; and IBV and AIV, respectively. Furthermore, 2.6% of these flocks were infected with IBV, NDV, and APV at the same time. On the other hand, 11.3% of these flocks were negative for the above-mentioned respiratory diseases. Our data showed that the above-mentioned respiratory pathogens were the most important causes of respiratory disease in broiler chickens in Jordan. Further studies are necessary to assess circulating strains, economic losses caused by infections and coinfections of these pathogens, and the costs and benefits of countermeasures. Furthermore, farmers need to be educated about the signs and importance of these pathogens.

Key Words: broiler • Jordan • respiratory pathogen • polymerase chain reaction • reverse transcription polymerase chain reaction


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Respiratory tract infections are of paramount importance in the poultry industry because high mortality may occur in poorly managed cases. The etiology of respiratory disease is complex, often involving more than one pathogen at the same time (Yashpal et al., 2004). A wide variety of pathogens have been associated with respiratory infections in poultry, including avian pneumovirus (APV), avian influenza virus (AIV), infectious bronchitis virus (IBV), Newcastle disease virus (NDV), and Mycoplasma gallisepticum (MG). These respiratory pathogens are of major importance because they can cause disease independently, in association with each other, or in association with bacterial or viral agents (Yashpal et al., 2004).

There is limited evidence in the literature describing the prevalence of poultry respiratory diseases in Jordan. One report describes the serotypes of IBV [Massachusetts (Mass), Arkansas (Ark), Delaware variant-072 (DE- 072), and JMK] in poultry flocks in Jordan based on a hemag-glutination inhibition test and demonstrates the exposure of chicken flocks in Jordan to Ark and DE-072, in addition to Mass-like serotypes of IBV (Saad, 2006). In a seroprevalence study, Al-Natour and Abo-Shehada (2005) found antibodies against AIV subtype H9N2 (71%) among broiler breeder flocks in Jordan. Gharaibeh and Algharaibeh (2007) investigated the role of APV as a factor in the respiratory disease of chickens in Jordan by serological and molecular methods, and found that APV antibodies were detected in 5 out of 23 broiler flocks (21.7%), 6 out of 8 layer flocks (75%), and 7 out of 7 broiler breeder flocks (100%), whereas APV nucleic acid was detected in 17 broiler flocks (12.8%) and 3 layer flocks (42.9%). All of the 20 detected APV isolates were subtype B. Saad and Dergham (2005) performed a serological and molecular study on MG in commercial poultry flocks suffering from respiratory disease in northern Jordan and found that the prevalence of MG in different types of chicken flocks was of 73.5% according to ELISA results and 31.6% according to isolation results, whereas random amplified polymorphic DNA testing of the 24 isolates revealed the presence of 5 banding patterns that were clearly different from the common MG strains of vaccine used in the field. In a seroprevalence study, Dergham et al. (2006) found antibodies against MG (80.43%) among broiler breeder flocks in Jordan. The high prevalence of MG in poultry flocks in Jordan, according to the previous reports of Saad and Dergham (2005) and Dergham et al. (2006), confirmed the endemic nature of MG in Jordan. Dergham et al. (2007) reported the appearance of NDV in vaccinated commercial broiler chicken flocks experiencing subclinical infectious bursal disease in Jordan.

The incidence and severity of respiratory disease in commercial broiler chicken flocks have increased recently in Jordan because of intensification of the broiler industry. Infectious bronchitis virus, NDV, AIV (H9N2), APV, and MG have been isolated several times from commercial broiler chicken flocks in Jordan (Jordanian Ministry of Agriculture, 2006). However, the roles of these agents, singly or jointly, in recent outbreaks of respiratory disease in broiler chicken flocks are not clear. This study was designed to clarify the roles of IBV, NDV, AIV (H9N2), APV, and MG, singly or jointly, in recent outbreaks of respiratory disease in broiler chickens in northern and central Jordan.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Broiler Flocks

During the period from December 2005 to July 2007, we examined 115 commercial broiler chicken flocks located in northern and central Jordan in which the chickens were suffering from severe respiratory disease. The flocks were kept for 40 to 45 d and then sent for slaughter. The broiler chicken vaccination program usually involved 2 live NDV and IBV vaccines administered either by spray or drinking water at 1 and 11 to 12 d of age and 1 infectious bursal disease (mild or moderate strains) vaccine administered by drinking water at 12 d of age. None of these flocks was vaccinated against AIV (H9N2) or APV. In the majority of flocks, signs of respiratory disease usually appeared at 33 to 35 d of age; chickens suffered from severe gasping, coughing, conjunctivitis, nasal and ocular discharge, depression, and weakness, and were reluctant to move. Watery greenish to brown diarrhea was observed on the farm. Gross lesions observed in these flocks included a moderate to severe congestion of trachea with or without mucopurelant exudates, airsaculitis, and peri-carditis or perihepatitis. Five tracheas per flock were collected at the acute phase of respiratory disease for both MG detection, by using PCR, and respiratory virus detection [AIV (H9N2), APV, IBV, and NDV], by using reverse transcription PCR (RT-PCR).

RNA Extraction

Tracheas from each flock were swabbed with sterile swabs (Heinz Herenz Medizin GmbH, Hamburg, Germany). Swabs were placed in 1,000 µL of PBS (pH 7.2) and were scraped on the side of the tube to facilitate removal of contents from the swab head. Extraction of RNA was performed on 60 µL of the pooled material for swabs from each flock [the remaining pooled swab materials were used for DNA extraction (MG)] with a Purescript RNA purification kit (Gentra Systems, Minneapolis, MN) according to the manufacturer’s procedure.

DNA Extraction

Extraction of DNA was performed on approximately 940 µL of the pooled material from swabs from each flock according to a previously described procedure (Liu et al., 2001).

RT-PCR

The respiratory virus detection primers (Alpha DNA, Montreal, Quebec, Canada; Table 1Go) used in this study were previously evaluated in previous studies and are listed in Table 1Go. One-step RT-PCR was performed by using an Access RT-PCR System kit (Promega Corp., Madison, WI) according to the manufacturer’s instructions. For each flock, there were 4 PCR tubes, 1 tube for each respiratory virus [AIV (H9N2), APV, IBV, and NDV]. Samples (4 PCR tubes, 1 for each respiratory virus) were amplified by using the following conditions and were carried out in a DNA Engine thermal cycler (Bio-Rad Laboratories Ltd., Mississauga, Ontario, Canada) in the same run and with the same program but with different annealing temperatures (each PCR tube for each respiratory virus was placed in a specific well according to it is annealing temperature) by using a temperature gradient program: RT-PCR was carried out for 1 reverse transcription cycle of 1 h at 45°C, followed by 94°C for 5 min, then 40 PCR cycles at 94°C for 45 s (denaturation), 53°C for 1 min [for AIV (H9N2)], 55°C for 1 min (for IBV and APV), 58°C for 1 min (for NDV; annealing), and 72°C for 90 s (extension), with a final extension cycle at 72°C for 5 min. Avian influenza virus (H9N2), NDV (LaSota), and IBV (M-41) antigens (Gezondheidsdienst voor Dieren BV, Animal Health Service, Deventer, the Netherlands), and APV subtype B live vaccine (Merial, Lyon, France) were used as positive controls for RNA extraction and RT-PCR. A negative control (nuclease-free water) was also used in each run.


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  		Table 1. Polymerase chain reaction primers used for respiratory pathogen detection
 
PCR

The MG detection primers used in this study were previously evaluated by Hantow et al. (1998) and are listed in Table 1Go. The PCR mix for MG was prepared in a volume of 50 µL containing 25 µL of master mix (5 units/µL of Taq polymerase, 400 mM deoxynucleotide 5'-triphosphate mixture, and 3 mM MgCl2), 18 µL of nuclease-free water (Promega Corp.), 1 µL (50 pmol/µL) of each downstream and upstream primer (Alpha DNA; Table 1Go), and 5 µL of DNA template. Polymerase chain reaction amplification was carried out in a DNA Engine thermal cycler (Bio-Rad Laboratories Ltd.) for 1 cycle of 5 min at 94°C, followed by 94°C for 1 min, 55°C for 1 min, and 72°C for 2 min for 35 cycles. The MG 6/85 strain vaccine (Intervet, Boxmeer, the Netherlands) was used as a positive control for DNA extraction and PCR. A negative control (nuclease-free water) was also used in each run.

Agarose Gel Electrophoresis

Polymerase chain reaction products were electrophoresed on a 2% agarose gel in Tris-acetate-EDTA buffer (40 mM of Tris and 2 mM of EDTA, with a pH value of 8.0) containing ethidium bromide (Promega Corp.) for 45 min at 100 V and visualized under UV light (AlphaImager, AlphaInnotech, San Leandro, CA).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Table 2Go represents the causes of respiratory infection in broiler chicken flocks included in this study according to the results obtained from PCR and RT-PCR. A total of 115 commercial broiler flocks with a history of respiratory disease were received. The results of this study showed that 13 and 14.8% of these flocks were infected with NDV and IBV, respectively, whereas 5.2, 6.0, 9.6, 10.4, 11.3, and 15.7% of these flocks were infected with both NDV and MG; MG and APV; IBV and NDV; IBV and MG; NDV and AIV; and IBV and AIV, respectively. Furthermore, 2.6% of these flocks were infected with IBV, NDV, and APV at the same time. On the other hand, 11.3% of these flocks were negative for the above respiratory diseases. Figure 1Go shows all assay controls for the above-mentioned respiratory pathogens.


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  		Table 2. Causes of respiratory infection in broiler chicken flocks
 

Figure 1
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  		Figure 1. Electrophoresis analysis (2% agarose gel) for avian respiratory pathogens. Lane M = 100-bp, 1.5-kb DNA ladder marker (Promega Corp., Madison, WI). Lane 1 = infectious bronchitis virus (IBV) positive control (positive; band at 383 bp). Lane 2 = Mycoplasma gallisepticum (MG) positive control (positive; band at 237 bp). Lane 3 = Newcastle disease virus (NDV) positive control (positive; band at 320 bp). Lane 4 = avian influenza virus (AIV) positive control (positive; band at 218 bp). Lane 5 = avian pneumovirus (APV) positive control (positive; band at 115 bp). Lanes 6 to 10 = negative controls for IBV, MG, NDV, AIV, and APV, respectively.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Respiratory diseases in poultry have been reported to be caused by mixed or single infections with several agents (Watanabe et al., 1977; Sakuma et al., 1981; Yashpal et al., 2004). Because all the tested flocks in this study were older than 32 d of age and were suffering from severe respiratory disease, our data suggest field exposure of these flocks to any of the 5 respiratory pathogens tested.

Infectious bronchitis virus was detected in 61 (53.04%) of the tested flocks (Table 2Go). Seventeen of these flocks (14.8%) were diagnosed as singly infected with IBV, whereas in the other flocks IBV was combined with other respiratory agent(s). Newcastle disease virus was detected in 48 (41.7%) of the tested flocks (Table 2Go). Fifteen of these flocks (13%) were diagnosed as singly infected with NDV, whereas in the other flocks NDV was combined with other respiratory agent(s). The high rates of IBV and NDV infections in broiler flocks (Table 2Go), according to RT-PCR in this study, suggest that IBV and NDV are the most important causes of respiratory disease in broiler flocks. It is a common practice in Jordan, as in other countries, to vaccinate broiler flocks against IBV and NDV at least twice as they reach 16 d of age. Despite the use of IBV and NDV vaccines, it is common to find NDV and IBV infections (Table 2Go) in vaccinated broiler flocks (Dergham et al., 2007). The results of this study may partially explain the failure of IBV and NDV vaccines and necessitate revising the vaccination program against IBV and NDV in Jordan. However, it is most likely that the flocks used in this study were also naturally exposed to a virulent strain of NDV or to new variant strains of IBV, which is why the vaccines were not covered.

Mycoplasma gallisepticum was detected in 25 (21.7%) of the tested flocks, and all these flocks were suffering from other respiratory agent(s) such as APV, IBV, or NDV at the same time. The high rate of MG infection in broiler flocks in this study was probably due to exposure of the broiler flocks to high virulent strains of MG. The results match those found by Saad and Dergham (2005) and Dergham et al. (2006). Although none of the flocks involved in this study was vaccinated against APV, APV was detected in 10 (8.7%) of the tested flocks, and all of these flocks were suffering from other agent(s) such as MG, IBV, or NDV at the same time. The lower detection rate of APV by RT-PCR may be because APV is present for only a few days after initial infection and because it replicates poorly in the infected host (Cook et al., 1993; Naylor et al., 1997; Cook and Cavanagh, 2001). Although all the tested flocks in this study were suffering from respiratory disease, none of these flocks exhibited swollen heads. This may indicate, in one way or another, the involvement of APV in the respiratory disease in those flocks.

Avian influenza virus subtype H9N2 has been reported in Middle Eastern countries and has been responsible for widespread and serious disease in commercial chickens in Pakistan (Naeem et al., 1999, 2003), Iran (Nilli and Asasi, 2001, 2003), the United Arab Emirates (Manvell et al., 2000), Saudi Arabia (Banks et al., 2000), Korea (Kwon et al., 2006), and Jordan (Monne et al., 2007). None of the flocks in this study was vaccinated against AIV (H9N2). Avian influenza virus was detected in 31 (27%) of the tested flocks in combination with other agent(s) such as IBV or NDV. The high prevalence of AIV in broiler flocks, according to this study, and in breeder flocks, according to Al-Natour and Abo-Shehada (2005), confirms the endemic nature of AIV (H9N2) in Jordan.

Thirteen tested flocks (11.3%) were diagnosed as negative for the above-mentioned respiratory pathogens. This failure of detection of the above-mentioned respiratory pathogens excluded these pathogens as the cause of this respiratory disease in these flocks. The respiratory disease in these flocks could have been caused by other respiratory pathogens, such as Escherichia coli, Mycoplasma synoviae, and Ornithobacterium rhinotracheal, or by management factors. However, determination of the exact cause of the respiratory disease, other than the above-mentioned respiratory pathogens, was not the aim of this study.

In general, 76 (58.3%) of the tested flocks were positive for any 2 of the above-mentioned respiratory pathogens (Table 2Go); 32 (27.9%) were positive for only 1 of the IBV or NDV; 3 (2.6%) were positive for the NDV, IBV, and APV at the same time; and 13 (11.3%) of these flocks did not show positive results for any of the above-mentioned respiratory pathogens.

Our data showed that these respiratory pathogens were the most important causes of respiratory disease in broiler chickens in Jordan. Further studies are necessary to assess circulating strains, economic losses caused by infections and coinfections of these pathogens, and the costs and benefits of countermeasures. Furthermore, farmers need to be educated about the signs and the importance of these pathogens.


   ACKNOWLEDGMENTS
 
This study was funded by Provimi Jordan. The author wishes to thank Paul Gerady (general manager, Provimi Jordan); deepest gratitude is also extended to Reinder Prack, Waheed Totanji, Ibrahim Shaheen, and Du’aa Al Salhey.

Received for publication October 9, 2007. Accepted for publication November 1, 2007.


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 DISCUSSION
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