Prevention Control and Management of Ranikhet Disease in Poultry

Saanvi Bhatia 2^nd year, BVsc and AH
Satuti Sharma and Rakshita Sharma Assistant professor, Department of Veterinary Pathology
Khalsa College of Veterinary and Animal Sciences, Amritsar, Punjab
Corresponding author Email: satutisharma586@gmail.com

INTRODUCTION

Domestic Poultry production plays an essential role in generating income and it has emerged as an industrial activity since there are nutritionally beneficial food such as eggs and meat can be derived from them. It needs to be understood that there are several challenges faced in such field when it comes to rearing poultry for our needs. Therefore, we should be well aware about the various outbreaks of diseases that are common in poultry production industry. One of the most important diseases in poultry sector is NewCastle Disease, also known as Ranikhet Disease and is identified as a public health threat. (1)

Ranikhet Disease is named so because it was first seen in Ranikhet, in Kumaon Hills located at Nainital which was recorded by Edward in 1927 and ever since it has become an endemic disease of poultry. The name NewCastle Disease on the other hand was coined by Doyle (2). It is a highly contagious avian viral disease which affects many domestic birds as well as wild birds and is responsible for high morbidity and mortality in naive, poorly vaccinated or non-vaccinated birds while the production performance in vaccinated birds is also affected (3).

AETIOLOGY

The disease is caused by Avian Paramyxovirus-1 serotype which is formed by group of closely related viruses that are responsible for causing NewCastle disease. Paramyxovirus is a single stranded, negative sense RNA virus with a helical symmetry and has an envelope. The envelope has certain glycoproteins or spikes on its surface which are of two types, that is HN glycoprotein which has both haemagglutinin and neuraminidase activity and the other is (F) Fusion glycoprotein (2,3).

The interesting feature about this virus is that it is able to produce different signs and lesions in the host species due to the presence of different pathotypes of the same virus which are listed below:

1.Viscerotropic Velogenic -This form is also known as Doyle’s form. It is the most dangerous and highly virulent form which is responsible for producing hemorrhages in intestine.

2.Neurotropic Velogenic – This form is also known as Beech form and is responsible for producing respiratory and nervous signs.

3.Mesogenic- This is a mild form of the virus and is also known as Beaudette form which produces only respiratory signs and sometimes nervous symptoms but low mortality is recorded from this form.

4. Lentogenic – This form is also known as Hitchner form and is a very mild form which produces inapparent respiratory infections.

5.Asymptomatic-This form produces no such signs or lesions. (4)

SPREAD

The spread of this disease may occur by several ways such as if an infected bird shows respiratory symptoms, then the spread of virus can be by aerosols of mucous which may be inhaled by vulnerable birds. This method of transmission is very quick. The infected birds also shed virus in feces which may be ingested by birds, either directly or in contaminated feed or water which is a slow method of transmission. Humans also aid in transmission of virus in the poultry farm if they deal with contaminated objects, fomites or poultry products and unsterilized tools (2).

PATHOGENESIS

After the entry of the virus in the body, the virus attaches to the surface of host cell to the cell receptors. This process occurs with the help of HN Glycoprotein which is present on the surface of envelope of virus. Following this step, the viral envelope fuses with the membrane of host cell which is mediated by Fusion (F) glycoprotein and is initially present as FO which is a non-functional precursor. The FO is to be cleaved into F1 and F2 by a host protease. Only cleaved FO is capable of fusion of viral envelope to cell membrane which is essential for infection in the host cell. The post translational cleavage occurs with the help of host cell protease on the cleavage site. The failure to be cleaved would result in non- infectious viral particles. Moreover, there are several proteases present in the host’s body that can cleave F0 but which enzyme cleaves F0 depends upon the amino acid sequence present on the cleavage site. If there is presence of monobasic amino acid sequence then trypsin like protease would cleave the site which is present in intestine and respiratory tract. These are called low virulent New Castle Disease Virus that is, lentogenic virus. The virus which has multi basic amino acid sequence is cleaved intracellularly by ubiquitous furin- like proteases. (5). These viruses are virulent strains of New Castle Disease Virus which can invade any tissue or organ and cause generalized infection ultimately leading to death. (2)

CLINICAL SIGNS

The disease is manifested as varying signs depending upon the pathotype of Newcastle Disease Virus infecting the host and may vary greatly in mortality and morbidity to asymptomatic carriers. Moreover, other factors that determine the observed symptoms are the immunity of host, species of host, age, coinfection with other organisms, environmental or any other kind of stress, route of exposure or the dose of virus (5).

In viscerotropic velogenic strains, that is a highly virulent strain, the disease manifests itself as sudden and high mortality and the signs observed as such are listlessness, depression, prostration, oedema of eyes and head, sudden drop in egg production, cyanotic combs, increased respiration rate, green diarrhea and nervous symptoms may be seen. Neurological symptoms may be seen in the birds which survive the initial phase of infection. In these susceptible birds, mortality reaches 100% in the flock. In Neurotropic velogenic, Respiratory symptoms and neurological symptoms may be seen. Signs like depression, inappetence, drop in egg production and coughing may be seen.

In mesogenic strains, that is low virulent strains, respiratory symptoms and usually nervous symptoms are also observed. In adult laying hens, there will be a marked drop in egg production that lasts for several weeks. Mortality in the flock reaches 50% or more. In lentogenic strains, that is virus of low virulent strain, mild respiratory symptoms are observed for a short time (6). In lentogenic strains, mild respiratory symptoms and no nervous symptoms are seen. This strain is used for producing vaccines against Newcastle disease virus.

Clinical signs produced by a specific virus may be seen differently in one bird from another. For instance, turkeys are less susceptible from Newcastle Disease Virus as compared to chicken and hence symptoms observed in them are less severe (2,6).

GROSS LESIONS

The different pathotypes of the virus are the determining factors of the gross lesions observed.

In the viscerotropic velogenic strain, the lesions observed are hemorrhages on the serosal surface of intestine which are particularly observed in proventriculus, caeca and small intestine. The enlarged and necrotic caecal tonsils are known as the ‘old faithful’ lesion of Viscerotropic Velogenic NewCastle disease. Enlarged spleen and perithymic hemorrhages are also usually observed. Eyelid edema is also one of the consistent findings in carcass of infected birds. In the case of neurotropic velogenic strain infection. Gross lesions are absent.

Mesogenic strains of Newcastle Disease virus are responsible for respiratory lesions. Moreover, misshaped eggs, splenomegaly and some degrees of conjunctivitis is also seen. Lentogenic strains of virus produce low mortality and lesions observed are tracheal hemorrhages, air sacculitis and splenomegaly (7). Congestion was observed in organs like spleen, liver, kidney, lungs and intestine.

MICROSCOPIC LESIONS

There are a variety of microscopic lesions seen in tissues affected by Newcastle Disease Virus, therefore they are of no use in diagnosis. Some of the lesions are seen in intestine, proventriculus, brain and several other organs. In proventriculus, cecal tonsils and intestine there is desquamation of epithelial cells and hyperemia of muscularis layer. There are hemorrhages, necrosis and infiltration of inflammatory cells in liver (8). Necrosis of lymphoid tissue is seen all over the body especially in gut associated lymphoid tissue. In the nervous system, non-purulent encephalomyelitis along with neuronal degeneration is seen, which occurs in the cerebellum, medulla, mid brain but rarely in the cerebrum. Fibrinoid necrosis of blood vessels was observed in spleen and along with that moderate swelling of hepatocytes and diffused mild sinusoidal and blood vessel congestion was seen in liver. Trachea and kidneys reveal mononuclear cell infiltration (9).

DIAGNOSIS

There are no symptoms or lesions that are regarded as pathognomonic for this disease; therefore the diagnosis of this disease is not done on the basis of signs or lesions. Virus isolation can be done from clinical samples like cloacal swabs, tracheal swabs and intestinal contents. Newcastle Disease Virus can also be grown in embryonated eggs, BHK21 cell line and pig kidney cell line. The presence of specific antibodies in the serum of the bird can be a way of diagnosis. Serological tests like ELISA, AGPT, Virus neutralisation in chick embryos, plaque neutralisation and single radial immunodiffusion tests can be used. The most widely used method for diagnosis of this disease is Haemagglutination inhibition test.

The essential part of diagnosis is to differentiate one strain of the virus from another which can be done by group of monoclonal antibodies to see if they are reactive. Moreover, the disease should also be differentiated from other avian paramyxovirus infection. Avian paramyxovirus 2 affects chickens and turkeys and it is clinically manifested as respiratory symptoms in them. Avian paramyxovirus 3 affects turkeys and it is manifested in the form of respiratory disease (2). This disease should be differentiated from laryngotracheitis, fowl pox (diphtheritic form), psittacosis, aspergillosis and infectious bronchitis (6).

CONTROL AND PREVENTION

Control of this disease can be done by vaccination. The following vaccination is used:

1. Live mesogenic strain vaccines- These vaccines are used where Newcastle Disease is epidemic. The vaccines are Mukteswar, Komarov and Roakin.
2. Live lentogenic strain vaccines- These are the most widely used vaccines. These are La Sota and B1.
3. Inactivated vaccines- These are produced by growing the virus in the eggs, where the preferred route is allantoic fluid and it is treated with formalin or Beta propiolactone so that it is inactivated.
4. Viral vectored vaccines- One of the examples of this vaccine is NDV-vectored vaccine. Bivalent and Multivalent vaccines are produced against Newcastle disease and other infectious poultry diseases.
5. Experimental Newcastle disease vaccines- The examples are Recombinant Subunit Vaccines and virus- like particle vaccines. (10)

The eradication can be done by biosecurity along with regular vaccination schedule, proper hygiene and minimum movement in poultry farm.

PUBLIC HEALTH IMPORTANCE

If exposed to large amounts of virus, humans who work in laboratories may be infected by Newcastle Disease virus which is manifested by conjunctivitis and the virus is shed from ocular discharge for 4-7 days. However, it is resolved rapidly.

Therefore, it is important that one should take all the safety measures while working in laboratories to reduce exposure to the virus (6).

REFERENCES

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2. Vegad, JL. and Katiyar, AK. 2001.A Textbook of Veterinary Special Pathology, Infectious diseases of livestock and poultry. International book distributing Co.
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10. Hu, Z., He, X., Deng, J. et al. Current situation and future direction of Newcastle disease vaccines. Vet Res 53, 99 (2022). https://doi.org/10.1186/s13567-022-01118-w