The Common Respiratory Diseases of Poultry in Bangladesh: Present Status and Future Directions

Md. Taimur Islam1*, Mirza Mienur Meher2, Anas Bin Harun3 and Md. Golam Haider1

1Department of Pathobiology, Faculty of Veterinary Medicine and Animal Science, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur-1706, Bangladesh; 2Department of Microbiology and Public Health, Faculty of Veterinary Medicine and Animal Science, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur-1706, Bangladesh; 3Faculty of Veterinary Medicine and Animal Science, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur-1706, Bangladesh.

Editor | Muhammad Abubakar, National Veterinary Laboratories, Park Road, Islamabad, Pakistan.

Received | April 19, 2022; Accepted | May 13, 2022; Published | May 21, 2022

*Correspondence | Md. Taimur Islam, Department of Pathobiology, Faculty of Veterinary Medicine and Animal Science, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur-1706, Bangladesh; Email: [email protected]

Citation | Islam, M.T., Meher, M.M., Harun, A.B., and Haider, M.G., 2022. The common respiratory diseases of poultry in Bangladesh: Present status and future directions. Veterinary Sciences: Research and Reviews, 8(1): 52-64.

DOI | https://dx.doi.org/10.17582/journal.vsrr/2022.8.1.52.64

Keywords | Respiratory diseases, Poultry, Avian influenza, NDV, Incidence

Copyright: 2022 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Introduction

Among all the body systems of poultry, the respiratory tract is an important part where pathogens are frequently responsible for respiratory diseases (Bhuiyan et al., 2019). The respiratory system of avian species starts with the nostril and completes with the lungs and air sacs (Tully, 1995). Bird lungs are firm and fixed in the thoracic cavity. The rigid network allows only minimal expansion of the blood capillaries to increase blood flow. The respiratory system as its main function utilizes a relatively small, rigid, flow-through lung to exchange oxygen and carbon dioxide between the gas and the blood. The system of air sacs that act to move the gas through the lung also participates in this function (Doğan and Takaci, 2018). It serves as a vital pathway for pathogens to enter the body systems and hosts a diverse range of commensal and pathogenic organisms such as bacteria, viruses, and fungi that interact with one another, thereby regulating the magnitude of the disease complex (Samy and Naguib, 2018). This is the key challenge for veterinarians to diagnose the disease properly (Baskerville, 2011). The intensive methods of commercial poultry rearing are mainly responsible for the significant increase in avian respiratory diseases worldwide (Samy and Naguib, 2018). In Bangladesh, commercial poultry systems are mainly divided into layers, broilers and sonali chicken farms (Imam et al., 2020). Avian influenza (AI), Newcastle disease (ND), infectious bronchitis (IB), infectious laryngotracheitis (ILT), and avian metapneumovirus are the most common viral diseases to affect the avian respiratory system in commercial poultry farms in Bangladesh, while mycoplasmosis, fowl cholera, and infectious coryza are the most common bacterial diseases, and aspergillosis is the most common fungal diseases to do so. Every pathogen has a different infection pattern, transmission system, clinical symptoms, control strategy and vaccination program (Ali, 2018). However, due to similarities in clinical signs of many diseases, it becomes difficult to differentiate based on their lesions.

On the other contrary, the occurrences of diseases vary depending on the geo-climatic condition, season, breed and age of the bird. Diagnosis of the disease is very important for the proper treatment of a disease. For diagnosis of a disease, clinical signs, gross tissue changes and histopathological examination are very important. Some microscopic examinations and bacteriological tests are performed for confirmatory diagnosis. Among the various diagnosis procedures, a necropsy is critical to diagnosing the disease (Nooruzzaman et al., 2019a).

Bangladesh with its population of 160 million people within an area of 1,47,570 square km is one of the most highly populated countries in the world (Islam et al., 2014). It has been reported that there are about 320.63 million poultry population in Bangladesh and around 120 million egg per day and 1363 tons of meat per day has been produced (Rahman et al., 2018). The economic growth and development of Bangladesh greatly depend on the performance of the agricultural sector where livestock plays an important role. The livestock sector contributes approximately 2.95% and 17.5% of the country’s gross domestic product (GDP) and the agricultural GDP, respectively. The commercial poultry industry has the potential to increase income, reduce malnutrition, provide employment opportunities, and alleviate poverty in the livestock sector (Begum et al., 2010). Poultry diseases, however, are the major impediment to the development of this industry in Bangladesh and there is the dearth of information regarding prevalence, pathology and necropsy findings of avian respiratory diseases. Hence, critical analysis of different respiratory diseases of poultry is essential to protect the poultry farm from economic losses. Considering the above-mentioned points this study was aimed to describe the aetiology, clinical signs, necropsy findings and prevalence of the respiratory diseases by critically reviewing the previous research in different areas of Bangladesh.

Common respiratory diseases of poultry in Bangladesh

The incidence of different respiratory diseases of poultry in different area of Bangladesh are presented int the Figure 1.

Avian influenza (AI)

AI is a significant, highly contagious, rapidly spreading, lethal viral disease of poultry caused by influenza A viruses of the family Orthomyxoviridae. Avian influenza virus (AIV) was responsible for causing this pandemic threat in 1918 as around 50 million people died worldwide, known as Spanish flu (Lüthy et al., 2018). The highly pathogenic avian influenza viruses (HPAIVs) were identified for the first time in Bangladesh in February 2007 by the Bangladesh Livestock Research Institute (BLRI). Since then, a significant number of outbreak waves have attacked the poultry industry in Bangladesh every year. Around 556 outbreaks have been reported in Bangladesh since 2007 (OIE, 2020). Highly pathogenic AI has drastic effects on economic and social impact, including zoonosis, a casualty in humans, losses of production, and impaired livelihood of vulnerable people (Bari et al., 2009).

 

Table 1: Prevalence of Avian Influenza (AI) H5 and H9 viruses in Live Bird Markets (LBM), Chittagong and Dhaka, Bangladesh.

Sample type	No. LBMs	H5 virus median prevalence (%)	H9 virus median prevalence (%)	Reference
Retail LBM	20	69.9	96.4	(Kim et al., 2018)
Mixed LBM	20	92.0	96.0

 

The virus has mutated several times and has changed its genetic clades from clade 2.2.2 to clade 2.3.2.1a. Clade 2.3.2.1a is now more virulent than other clades discovered in 2013 (Giasuddin et al., 2018; Nooruzzaman et al., 2019a). Based on the HA gene of H5N6, another clade, 2.3.4.4, was discovered in 2016 (Giasuddin et al., 2018). Compared to other seasons, AI is more prevalent in winter and spring. Recent surveillance revealed that AIV was found in nearly all the live bird markets (LBM) in Dhaka and Chattogram. H5 is more prevalent in waterfowl than in chickens, whereas H9 is more common in commercial chickens than waterfowl. Commercial broilers are more susceptible to H9 than indigenous breeds and cross-breed reports.

In Bangladesh, AIV has been isolated from chickens, ducks, geese, quails, turkeys, pigeons, crows, and some migratory birds and mammals like humans, bats, and monkeys (Nooruzzaman et al., 2019b). Reportedly, H5 and H9, or their co-circulation, are present in the air of LBMs, posing serious public health concerns (Rahman et al., 2020). LBMs of Bangladesh, therefore, act as a possible source of AIV transmission (Hassan et al., 2018). The symptoms of AI may vary significantly and range from being undetectable to a drop in egg production and even to high death rates. Cyanotic combs and wattles, edema of the head and face, ecchymosis, discoloration of the leg shanks, drowsiness, and huddling were all observed (Biswas et al., 2011).

AIV was found in 6.4% of veterinary hospital cases in Chattogram (Sabuj et al., 2019), 5.4% in Kishoreganj (Rahman et al., 2019), and 0.3% in Dhaka (Islam et al., 2014). On the other hand, domestic ducks play a vital role in transferring AIV when they are exposed to migratory birds of Central Asian flyway in the wetland areas of Bangladesh (Barman et al., 2017).

 

Necropsy examination of the dead birds showed cyanotic legs, comb, and wattle (Figure 2A). The musculature appeared to be hemorrhagic and congested. Petechial and ecchymotic hemorrhages were observed in the mucosa of the upper respiratory tract. Hemorrhages and congestion were also evident in the trachea, lungs (Figure 2B), heart, liver, kidney, spleen, and shanks. Swollen head and orbital sinuses were also reported. Egg follicles were also found congested and ruptured in the layer chickens. In the larynx and trachea, hemorrhages, hemorrhagic exudates, and cloudy air sacs were observed (Bari et al., 2009).

Microscopically, severely congested lungs and focal necrosis of liver parenchyma were observed, and the nuclei of affected cells appeared as karyorrhectic (Figure 3A). Severe congestion was evident in the central vein. In addition, the cardiac vessels appeared congested with focal my degeneration (Bari et al., 2009).

 

Strict biosecurity measures can aid in the control of AIV spread. For example, poultry farm workers may be trained to detect avian influenza infection signs in birds as part of biosecurity. In addition, there are two vaccines (HVT-H5 and RE-6) against AIV that the government approved in 2013, and they are now widely used in parent stock farms, but they are in short supply in marginal farms due to the high cost and scarcity of vaccines (Giasuddin et al., 2018).

Newcastle disease (ND)

ND is another highly contagious, often fatal viral endemic disease in the poultry industry causal agent of which is Newcastle disease virus (NDV), classified as avian paramyxovirus serotype 1 under the genus Avian orthoavulavirus 1 of family Paramyxoviridae, order Mononegavirales. It affects various domestic and wild birds (Barman et al., 2017). Based on the clinical disease produced in infected chickens, NDV strains have been classified into four virulence groups: velogenic (high virulence), mesogenic (moderate virulence), lentogenic (low virulence), and avirulent (asymptomatic). Velogenic strains have up to 100% mortality, whereas mesogenic ones have a lower level of mortality and cause respiratory signs. On the other hand, Lentogenic strains only cause mild or inapparent respiratory signs (Kabiraj et al., 2020).

It may cause 100% mortality (Biswas et al., 2005; Chukwudi et al., 2012) and decreased body mass and egg production of survived chickens. Therefore, ND is directly linked with the development of the rural economy and food safety and the nutritional safety of people as it causes high mortality and morbidity in commercial and backyard chickens. Differences in prevalence rates of ND in different regions in Bangladesh are insignificant. The prevalence of ND was highest in October, and the chickens aged between 0 and 3 months. (38.60%) (Rahman et al., 2011). The prevalence rate of ND was 6.73% in Sylhet (Islam et al., 2003), 7.1% in Gazipur (Islam et al., 2020), 7.2% in Dhaka (Giasuddin et al., 2002), 8.92% in Narsingdi (Uddin et al., 2010), 9.83% in Barishal (Meher et al., 2020), 11% in Chattogram, 11.24% in Bogura (Talukdar et al., 2017), 11.78% in Kishoreganj (Mamun et al., 2019); 13.84% in Sylhet (Biswas et al., 2005), 14.1% in Dhaka division (Islam et al., 2014), 17.8% in Ramu, Chattogram (Sabuj et al., 2019), 21.6% in Kishoregonj (Rahman et al., 2019), 25% in Mymensingh (Rahman et al., 2012). Regarding the type of birds, the prevalence of ND was reported in layers 37.5%, broiler 32.5%, native birds 55.0%, duck 27.5% (Rahman et al., 2012), and 11.35% in quail (Islam et al., 2016).

Necropsy examination of dead chickens caused by ND showed hemorrhages on the tip of the glands of the proventriculus. Along with intestinal necrosis, button-like hemorrhagic lesions of purple-red to dark red were observed. The hemorrhagic lesion was also noticed at the cecal tonsil and under the cornified layer of the gizzard (Islam et al., 2020). In addition, hemorrhagic lungs were observed in the case of ND (Figure 2C). Microscopically, hemorrhage and infiltration of mononuclear cells were observed in the gizzard and proventriculus. Congestion and massive infiltration of mononuclear cells were also observed in the lungs (Figure 3B) (Islam et al., 2020).

Infectious bronchitis (IB)

Caused by infectious bronchitis virus (IBV), IB is a highly contagious and acute respiratory disease of paramount economic importance in commercial chicken flocks throughout the world. IBV is classified into the genus Gammacorona virus in the family Coronaviridae of the order Nidovirales. Characteristic signs of IB are usually found in the respiratory system, and decreased egg production, fragile, soft, deformed, irregular, or rough shells, shell-less eggs, and poor-quality eggs are also found in breeders and layers. Some strains of IBV are nephropathogenic, causing interstitial nephritis, particularly in chicks. It can also replicate and cause pathogenicity on non-respiratory epithelial surfaces, i.e., the kidneys and gonads (Cavanagh, 2007). IBV is shed through the respiratory tract and the faces, and it can live in the intestinal tract of the host for several weeks to months. IBV can survive in the litter for 56 days (de Wit et al., 2011).

Though it can affect all age groups, some studies showed that chickens from higher age groups are more susceptible to IB infection. Such as, 54.55% of prevalence was in 41-60 weeks (Bhuiyan et al., 2019a), and 76.92% was in 63-73 weeks aged layer birds (Meher et al., 2017). Several studies have been performed to investigate the prevalent rate of IB in Bangladesh. These studies show that IB has become endemic in Bangladesh and has been detected in the layers, broilers, backyard chickens, and quails (Islam et al., 2016, 2020). One study reported an overall 17.52% prevalence of IBV in Bangladesh, including 42.22% in commercial layers, 11.94% in broilers, 17.24% in Sonali, and 14.93% in broiler breeders. Chickens of these farms were vaccinated following a standard vaccine schedule against H120, MA5, and the IB 4/91 strain of IBV from a commercial source (Bhuiyan et al., 2019b). 

In the winter, IB infection was more prevalent (Bhuiyan et al., 2019a). District wise, the prevalence rate was 41.67% in Tangail, 24.42% in Mymensingh, 19.32% in Gazipur, 16.67% in Jamalpur, 15.38% in Dhaka, 13.68% in Bogura, 9.26% in Rangpur and 5.88% in Cumilla. Few more studies revealed the prevalent rate to be 3.2% in Gazipur, 0.29% in Sylhet, 0.24% in Narsingdi, 58% in Fatikchori, Chattogram (Barua et al., 2012), 77.83% in North-central region (Biswas et al., 2005) and 79.38% in Northern region (Das et al., 1970). IB cases in veterinary hospitals were reported to be 0.6% in Kishoreganj (Rahman et al., 2019) and 1.3% in Ramu Bazar (Sabuj et al., 2019). Biosecurity, management practices, vaccination status, and environmental factors may all play a role in the differences in IBV seropositivity.

Necropsy findings of IB-infected birds showed tracheitis with hemorrhage, congestion, and fibrosis in the lungs (Figure 2D). Egg production declined. Misshaped, depigmented, deformed eggs, and soft-shelled eggs were observed. Swelled, enlarged and pale kidneys with nephritis were evident, frequently with urate deposits in the tubules. Moreover, dilation of the oviduct was observed. Microscopically, the Infiltration of a considerable number of reactive cells, damage of tubular lining epithelium, distension of distal convoluted tubules, and edema of Bowman’s capsule were found in the kidney. In addition, hemorrhages and massive Infiltration of mononuclear cells were recorded in the trachea and lungs (Islam et al., 2020).

Infectious laryngotracheitis (ILT)

The poultry industry faces ILT as another significant threat (Islam et al., 2010). ILT is a significant avian respiratory disease caused by the infectious laryngotracheitis virus (ILTV). The virus is classified into the genus Iltovirus in the family Herpesviridae in the subfamily Alphaherpesvirinae (Islam et al., 2010). Taxonomically the virus is known as Gallid herpesvirus 1 (Roizman, 1982). chickens actively shedding ILTV can also naturally infect pheasants and peafowls through contact. ILTV is transmitted via the upper respiratory and ocular routes. Clinical signs include nasal discharge, conjunctivitis, and decreased egg production. Coughing, expectoration of bloody mucus, gasping and marked dyspnea leading to suffocation are common in severe cases. Death may occur due to obstruction of the trachea by hemorrhage or exudates. The mortality rate can reach up to 70% (Fuchs et al., 2007). Recovered birds can serve as carriers indefinitely (Kirkpatrick et al., 2006). The layer chick­ens are primarily associated with ILT infection in Bangladesh (Rahman et al., 2018). The higher seropositivity in layer chickens may be due to the disease being more prevalent in older chickens than younger ones.

Seroprevalence of ILTV was 100% in Rajshahi, Chattogram, Khulna, and Barishal divisions had the seroprevalence of 100%, whereas it was 87.80% in Dhaka and 84.37% in Rangpur (Jahan et al., 2012). Another study reported that, particularly in commercial layer farms in Chattogram, the seroprevalence of ILTV was 17.33% (Uddin et al., 2014). The seroprevalence of ILTV was observed higher in winter (24%) in comparison to summer (12%) and the rainy season (16%). Chickens from the 10-35 weeks of age group are more susceptible to ILTV. Therefore, strict biosecurity, proper management practices, and vaccination are essential to prevent ILT.

Necropsy examination of ILT-infected dead birds showed severe hemorrhage in the lungs and trachea with occlusion of the tracheal lumen by mucus, caseous exudates, and blood (Figure 2E). In addition, congestion and fibrosis were observed in the lungs (Islam et al., 2020). Microscopically, hemorrhagic lungs were observed in the lungs. Moreover, hemorrhage and destruction of epithelial lining were found in the trachea (Figure 3C) (Islam et al., 2020).

 

AMPV or swollen head syndrome

AMPV, also known as avian rhinotracheitis virus, causes highly contagious respiratory disease and is classified into the genus Metapneumovirus in the family Pneumoviridae of the order Mononegavirales (Pringle, 1998). It causes acute upper respiratory tract infection in turkeys and chickens (Cook and Cavanagh, 2002), with swelling of the periorbital tissues and infraorbital sinus being the characteristic clinical signs in chickens. Therefore, this condition is known as a swollen head syndrome. Torticollis, sneezing, coughing, nasal discharge, and watery eyes are common clinical signs of this disease in broiler flocks and breeders (Shin et al., 2000). Reduced egg quality and declined egg production in layers and broiler breeders were also observed (Gharaibeh and Algharaibeh, 2007). AMPV was reported for the first time in Bangladesh in 2016 (Ali et al., 2019). Seroprevalence of AMPV was 70.07% in Gazipur, 59.83% in Mymensingh, 53.44% in Rangpur, 41.26% in Bogura, and 39.40% in Panchagar. It has also been reported that broiler breeders had higher (72.30%) seropositivity than layer (50.85%) and Sonali (35.57%) type chickens. Antibodies of AMPV were higher in broiler breeder flocks aged over 41 weeks, and sensitivity was higher in winter (68.21%) season (Ali et al., 2019). Another study reported that the seroprevalence of AMPV was 2.60% in Sonali chicken, and no broiler chicken was found positive (Bhuiyan et al., 2019a). Prevention requires good management practices with a high level of biosecurity and vaccination.

Mycoplasmosis

Mycoplasma gallisepticum (MG) is an economically important organism in the commercial poultry industry in Bangladesh. It is a member of the family Mycoplasmataceae and affects chickens and turkeys, causing avian mycoplasmosis or chronic respiratory disease (CRD), which results in a decrease in food conversion ratio (FCR), decreased egg production with hatchability, and increased production costs (Kempf and Gesbert, 1998). Furthermore, the pathogenicity of mycoplasmosis becomes more drastic due to secondary bacterial infection, mainly Escherichia coli (Ali et al., 2017).

The overall seroprevalence of MG in Bangladesh was 64.47%, with 68.77% being in Sonali, 63.74% in ISA brown, and 59.37% in white leghorn layer type chickens (Ali et al., 2017). The prevalence rate of MG was 62.44% in Feni (Sarkar et al., 2005), 55.13% in Rajshahi (Hossain et al., 2007), 46.88% in Patuakhali (Sikder et al., 2005), and about 13% in Gazipur and Bogura (Ahmed et al., 2009; Talukdar et al., 2017). Veterinary hospital case records indicated the prevalence to be 12.79% in Bogura (Talukdar et al., 2017), 4.38% and 11.66% in Sylhet (Rahman and Adhikary, 2016), 9.16% in Kishoregonj (Mamun et al., 2019), 7.6% in Dhaka (Islam et al., 2014) and 4.8% in Kishoregonj (Rahman et al., 2019). Prevalence of mycoplasmosis is higher during the winter season and just before the winter season (Haque et al., 2015; Sarkar et al., 2005). Chickens from all age groups are susceptible to mycoplasmosis (Kabir et al., 2021). 

Necropsy examination of the chickens and ducks diagnosed with mycoplasmosis showed cloudy air sacs, fibrinous perihepatitis, fibrinous pericarditis, and fibrinous pleuritis. In addition, cheesy materials were evident in the air sacs. In some cases, congested tracheas were observed (Islam et al., 2020; Talukdar et al., 2017). Microscopically, fibrinous perihepatitis, fibrinous pericarditis, fibrinous pleuritis, and inflammatory cell infiltration were found in the liver, heart, and lung, respectively (Figure 3D) (Islam et al., 2020). 

Fowl cholera

Fowl cholera, a septicemic disease, is one of the most important infectious bacterial and devastating avian diseases of poultry and wild birds caused by Pasteurella multocida subspecies multocida (P. multocida) in the family Pasteurellaceae (Xiao et al., 2016) and has been considered as an economic disease worldwide. It may attack the respiratory system and cause respiratory distress, cellulitis of the face and wattles, and mucous discharge from the mouth and nose (Ali and Sultana, 2015). P. multocida has five capsular serotypes (A, B, D, E, and F), and each serotype is generally associated with a specific host. Among these serotypes, serotype A causes fowl cholera in avian species (Harper et al., 2006). Laying flocks are mostly more susceptible to fowl cholera than younger chickens (Wang et al., 2009). Prevalence of fowl cholera was 5.26% in Kishoregonj (Mamun et al., 2019), 4.1% in Gazipur (Islam et al., 2020), 3.90% in Dhaka (Giasuddin et al., 2002), 3.6% in Kishoregonj (Sabuj et al., 2019), 0.44% and 2.7% in Sylhet (Islam et al., 2003), and 6.76% in northern and northcentral districts of Bangladesh (Biswas et al., 2005). 

Necropsy findings of chickens with fowl cholera showed petechial hemorrhages on the heart base. Dark-colored liver with pinpoint white round numerous necrotic spots were evident. In some cases, enteritis was also observed (Islam et al., 2020).

Infectious coryza

Infectious Coryza (IC) is a contagious respiratory disease caused by Avibacterium paragallinarum of the Pasteurellaceae family of bacteria that affects several avian species (Blackall and Reid, 1982). The disease may be acute or subacute in the early stages, but it progresses to a chronic state as it spreads through the flock. This disease can affect chickens of all ages. Conjunctivitis with swelling of the sinuses, face, wattles, Nasal discharges, diarrhea, decreased feed and water consumption, decreased egg production, retarded growth in younger chickens, and an increased number of culls are clinical signs of this disease (Akter et al., 2016).

Infectious coryza has a higher prevalence rate in laying hens (52.8 %) and growing hens (42.8 %) in comparison to the pre-laying stage (16.6%). The prevalence was 0.97% in Kishoregonj (Mamun et al., 2019), 0.37% in Sylhet (Islam et al., 2003), 0.32% in Narsingdi (Uddin et al., 2010), and 0.2% in Gazipur (Hassan et al., 2016) according to the veterinary hospital records.

Necropsy findings of chickens with infectious coryza showed mucous in the nasal passage, conjunctivitis, swelling of the face and sinuses, and congested lungs.

Aspergillosis

In Bangladesh, chickens’ most common fungal respiratory disease is Aspergillosis, caused by the opportunistic and ubiquitous saprophytic genus Aspergillus, particularly Aspergillus fumigatus (Sultana et al., 2015). Overcrowded, warm, humid environment of the farm sheds, wet litter or soil, moldy or dusty feeds, and poor ventilation serve as the predisposing factors for the growth of this fungus. The chicken’s constant inhalation of fungal spores results in clinically apparent infection (Dyar et al., 1984). The disease can occur as an acute form with high morbidity and mortality in young chickens, especially in brooding age called brooder pneumonia (Badhy et al., 2003), also occur as a chronic form in older chickens. Clinical signs of the disease include dyspnea, gasping, cyanosis of unfathered skin, and hyperemia (Sultana et al., 2015). Rainy season and winter season, 0-21 days of the age of birds, and use of sawdust as litter (7.69%) are the significant risk factors in Bangladesh (Islam et al., 2003; Sultana et al., 2015; Uddin et al., 2010). Prevalence of Aspergillosis was 7.98% in Narsingdi (Uddin et al., 2010), 7.33% in Sylhet (Rahman and Adhikary, 2016), 6.6% in Kishoregonj (Sabuj et al., 2019), 4.3% in Gazipur (Islam et al., 2020), and 0.33% in northern and north-central districts (Biswas et al., 2005).

Necropsy examination of dead chickens caused by Aspergillosis showed multiple hard creams to yellow-colored, circumscribe plaques a few mm to several cm in diameter seen throughout the lungs surface (Figure 2F), scattered in the ventral surface of sternum and air passages. The plaques were also observed in the air sacs, liver, syrinx, and intestines. Lung parenchyma was consolidated and congested, with single or multiple necrotic areas visible on cut surfaces of the lungs (Sultana et al., 2015). Microscopically, white color nodules were found in the lungs and air sacs (Islam et al., 2020).

Future directions to fight against respiratory diseases

The fundamental steps to inhibit the establishment of respiratory diseases and prevent further spread in a poultry farm are performing strict biosecurity, establishing and maintaining immunity, and vaccination. In addition, disease control is the crucial element for establishing a sustainable poultry industry. Therefore, the following initiatives should be taken to control the disease:

1. Commercial farms should be established in a planned way.
2. We should have a national poultry policy.
3. Farmers must have to start a farm with basic knowledge of biosecurity.
4. Ventilation in a commercial farm is the critical key to reducing the respiratory problems of the chickens and reaching the highest productivity and the highest conversion rate. Proper ventilation is vital for introducing clean outside air into a poultry house to replace indoor polluted air by eliminating harmful gases in the bird’s respiratory system, such as ammonia and gases arising from heater operation, and replacing the carbon dioxide with oxygen to let birds breathe well. Litter moisture and indoor relative humidity control are very crucial in poultry farms. Wet litter can contribute to the replication of microorganisms and increased ammonia production.
5. Bangladeshi strains of chicken should be developed. We must reduce our dependency on importing chicks, medicine, vaccines, etc., from other countries. Increased costs and poor availability of feeding ingredients, medicine, and vaccinations, will have a detrimental impact on the industry’s growth.
6. The quality of feed ingredients must be rigorously maintained.
7. Coverage by veterinary services must be expanded to promote production and minimize the risk of disease and animal loss.
8. We should establish vaccine manufacturing facilities and develop vaccines for harmful local strains.
9. Doctors, farmers, scientific personnel, government organization, and non-government organization have to work together. We have to arrange training programs for farmers, trainers, consultants, and doctors. 

Conclusions and Recommendations

Various respiratory diseases are highly prevalent in different poultry farms (layer, broiler, Sonali, and duck), including backyard chickens in different parts of Bangladesh. This is a critical challenge for veterinarians to diagnose the disease properly. It manifests that commercial poultry farming in Bangladesh is more complex regarding health management. Maintaining appropriate management practices, particularly a high degree of biosecurity, is crucial to reducing disease incidence and establishing sustainable commercial poultry. Additionally, a proper vaccination schedule might be a way to prevent poultry respiratory diseases in Bangladesh.

Novelty Statement

In every year the prevalence of respiratory diseases of poultry is very high in Bangladesh. Poultry farming with contemporary policy and maintaining the high level of biosecurity is crucial to reducing the incidence of respiratory diseases.

Author’s Contribution

MTI designed and executed the study. MMM and ABH collected the articles. MMM prepared the study map. MTI wrote the manuscript. MGH revised the manuscript. All authors contributed to include intellectual content.

Conflict of interest

The authors have declared no conflict of interest.

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