Avian Reo Virus

Plan of Talk

Introduction Economic importance Virus characteristics Transmission Clinical sings and PM lesions Treatment and control

Plan of Talk

Introduction Economic importance Virus characteristics Transmission Clinical sings and PM lesions Treatment and control

Introduction

1954 The initial avian reovirus was isolated by Fahey and Crawley

from the respiratory tract of chickens.1957 Olsen et al. Isolated a reovirus from chickens with naturally

occurring synovitis that were unrelated to MG or MS.Late 70s – early 80s Nonspecific malabsorption syndrome due to avian reovirus

was described.

Cont. …

Avian reo viruses are ubiquitous viruses in nature. They are commonly isolated from a variety of tissues in

poultry affected by multiple disease conditions such as:1. Viral arthritis/tenosynovitis.2. Stunting syndrome.3. Respiratory disease.4. Enteric disease.5. Malabsorption syndrome.

Cont. …

Reovirus infections are prevalent worldwide in chickens and turkeys.

Viral arthritis/tenosynovitis is found primarily in meat-type chickens and turkeys.

Reoviruses are commonly found in the digestive and respiratory tracts of clinically normal chickens and turkeys.

Cont. …

Highly contagious15% susceptible chicks are enough to spread through entire flock in the 1st week.

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Age-dependent susceptibilityEarlier the infection is associated with more severe and permanent weight suppression.

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10-30% weight suppression, without complications.

Up to 50% weight suppression, when complicated with other stressors.

Plan of Talk

Introduction Economic importance Virus characteristics Transmission Clinical sings and PM lesions Treatment and control

Economic Importance

Reovirus-associated Diseases;1. Weight suppression (malabsorption)

Infections in the first week of age.

2. Viral arthritis/ tenosynovitis Infections in naive birds (any age, but especially young).

3. Runting & stunting syndrome– Infections in the first week, reovirus + other agent(s).– Femoral head necrosis, brittle bone disease, acute mortality.

4. Respiratory disease.5. Enteric disease.6. Immune suppression.

Cont. …

Broiler 1. Increase mortality. 2. Viral arthritis and tenosynovitis. 3. General lack of performance;

1. Diminished weight. 2. Poor feed conversion. 3. Uneven growth rate. 4. Reduce marketability of affected birds.

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Breeder (viral arthritis prior to the onset or during egg production)1. Lameness.2. Increased mortality. 3. Decrease egg production. 4. Suboptimal hatchability and fertility. 5. Vertical transmission to progeny.

Plan of Talk

Introduction Economic importance Virus characteristics Transmission Clinical sings and PM lesions Treatment and control

Virus Characteristics

Family: Reoviridae Genous: Orthoreovirus Icosahedral symmetry Non enveloped 10 ds RNA

Cont. …

Persistent pathogen:1. Resistant to high temp 60c for 8 hrs.2. Tolerates pH 3-9.3. Non sensitive either. 4. Slight sensitive for chloroform.5. The virus can survive for up to 10 days on feathers, wood

shavings, glass, rubber and galvanized metal, and for 10 weeks in water, with limited effect on infectivity.

Cont. …

Sensitive to:1. 70% ethanol.2. 0.5% organic acid. 3. 5% hydrogen peroxide.

Virus Target Tissue

The epithelial cells of:1. Small intestine2. Bursa of Fabricius are the main sites of primary infection and portal of entry of the virus which rapidly spreads to other organs within 24-48 hours of infection.

Cont. …

The site where virus replication has the most serious consequences is the tibiotarsal-tarsometatarsal (hock) joint.

At this site, the virus replication and long-term persistence induce a series of processes leading to joint damage and in the most severe cases, tendon rupture.

Virus Kinetics

Experimental infection of adult SPF hens via the nasal, tracheal or esophageal routes, showed distribution of virus to all areas of the respiratory, enteric and reproductive tracts and the tendon of the hock joints (viraemia).

Cont. …

The virus was recovered from the plasma, erythrocyte and mononuclear cell fractions of blood within 30 hours.

By 3 to 5 days, virus had been distributed throughout the body.

Despite this widespread tissue dissemination, the principal site of virus replication is the enteric tract.

Plan of Talk

Introduction Economic importance Virus characteristics Transmission Clinical sings and PM lesions Treatment and control

Transmission

1. Vertical transmission, occurs at a low rate.2. Most chicks become infected at an early age from:

Small nucleus of congenitally infected hatch-mates. Environment.

Cont. …

Horizontal transmission1. Intestinal tract (fecal contamination) 2. Respiratory tract.3. Age related resistance.4. Reoviruses may enter broken skin of the feet of chicks from

the litter and become established in the hock joints.

Vertical Transmission5. Egg transmission low (<2.0%)6. Hens infected via oral, tracheal, and nasal inoculation were

able to transmit reovirus to their progeny.

Plan of Talk

Introduction Economic importance Virus characteristics Transmission Clinical sings and PM lesions Treatment and control

Clinical Signs – Post Mortem lesionsViral arthritis/tenosynovitis

Viral arthritis/tenosynovitisThe first signs of reovirus infection are usually observed in broiler breeder chickens between 6 and 10 weeks of age.

Broilers

Cont. …

1. Lameness.– Birds are reluctant to walk and

when forced up have a painful, trembling gait.

2. Joint swelling.– A distinct swelling of the

tendons of the shanks and also above the hock joint can be observed.

3. Thickened/ruptured tendons. Swollen tendons

Cont. …

4. Affected birds have malpositioned feathers, especially on the wings.

Malpositioned feather

Cont. …

5. The hock joint may be somewhat swollen, but usually not as severely as with Mycoplasma synoviae or Staphylococcus infections.

6. Upon opening the legs, the tendons usually appear discolored, brown or blood-tinged, with straw colored fluid between them.

Cont. …

7. Ruptured tendons may occur and, in older broiler breeders (29-30 weeks old), one may feel a hard scarry knot in the tendon above the hock joint.

8. When the infection is complicated by MS or Staphylococcus, the fluid may appear yellow and creamy.

Clinical Signs – Post Mortem lesionsMalabsorption Syndrome

The disease is mainly observed in broiler flocks.

Cont. …

1. History of diarrhea, beginning at few days of age and lasting until 10-14 days of age.– Light or dark brown, foamy droppings can be found with undigested

food particles.

2. Runting/Stunting.3. Abnormal feathering.

– Several affected broilers in a flock may exhibit malpositioned feathers, especially on the wings.

Cont. …

4. Skeletal abnormalities. – Early rickets with extreme paleness of legs and heads can be

observed.

5. At a later age (5-6 weeks) osteoporosis becomes clinically evident. – Frequently unilateral causing the birds to limp.

6. Delayed growth of the affected birds. 7. Mortality is variable and in general as low as 4 %.

Plan of Talk

Introduction Economic importance Virus characteristics Transmission Clinical sings and PM lesions Treatment and control

Treatment and Control

Treatment is impossible. Vaccinating breeders helps reduce problems in the progeny. Strict hygienic and sanitary measures will reduce the

incidence of the disease.

Purpose of Vaccination

1. Prevent infection of breeders.2. Prevent egg transmission to progeny.3. Produce maternal antibodies for the progeny.

Layers

Time of Vaccination

Broiler progeny need high MDA to prevent early infections, Infection before 7 days leads to malabsorption, runting and

stunting. Infection before 14 days leads to leg problems (FHN and

ruptured tendons).

Vaccination Program

For the development and persistence of high levels of maternal antibody, Giambrone recommended the use of:

1. Live vaccine as a primer early in life.2. Inactivated vaccine given at 6 weeks of age and again

prior to lay.

Cont. …

In areas of high exposure Chicks are susceptible during the first weeks of life, and early

vaccination becomes mandatory. In these areas, vaccination should begin at 7 days of age. Re-vaccination is recommended at 5 to 7 weeks of age and

again at 9 to 11 weeks.

Cont. …

In areas where there is less exposure Vaccination should be carried out at 5 to 7 weeks of age and

again at 9 to 11 weeks. To complete this program for breeding birds, the

administration of an inactivated Reovirus vaccine is recommended between 16 to 18 weeks of age.

Vaccine Strains

Strain Association Live/Killed

S1133 Tenosynovitis Live and Killed

UMI 203 Tenosynovitis Live

2408 Malabsorption/Tenosynovitis Killed

1733 Malabsorption/Tenosynovitis Killed

CO8 Malabsorption Syndrome Killed

305 Malabsorption/FHN/BBD Killed

ss412 Malabsorption/proventriculitis Killed

Virus Strains

Strain Disease or Syndrome Signs and Symptoms

1133Causes tenosynovitis (VA), an infection of the synovial sheath of the tendon.

Leg and or joint swelling, difficult in walking and bruised appearance of the leg and thigh muscles due to tendon rupture.

2408Associated with VA and Malabsorption Syndrome (MAS), a condition where nutrients are not absorbed in the intestine.

Early mortality, reduced weight gains, poor feathering, poor pigmentation, runting and stunting.

3005Associated with MAS, femoral head Necrosis (FHN), and brittle bone disease.

Deterioration of the top of the thigh bone can be seen during a post mortem examination.

Vaccine Administration

Route of Administration Efficacy

Subcutaneous (SQ) Good

Wing web Good

Water Good

In Ovo Poor

Why do we use live vaccines for REO virus? Are they used just as a primer or do they protect vaccinated birds against symptoms?

Live REO vaccines can induce protection against symptoms in young birds, but only when there are no maternally-derived antibodies (MDA) present to neutralize the vaccine.

Vaccines will not be effective in young birds with MDA against REO.

Early REO infections are the most dangerous ones. The most effective protection against them is by inducing high

levels of antibodies in the parent stock, to protect the offspring by MDA.

High antigen content inactivated REO vaccines are the most effective, inducing high titres in parent stock.

Priming such parent flocks with a live REO vaccine will further increase the effect of the inactivated REO vaccine.

Individual and average titres are higher and more uniform. Most importantly, the percentage of breeder birds that has

low or zero titres diminishes. This live priming of the young breeder birds can be done

when MDA have waned (after approximately six weeks of age).

Mal-absorption syndrome (MAS) is still a current problem in broiler flocks worldwide. Can it be minimized by REO virus vaccination of parent stock?

MAS is a complex of symptoms occurring when the intestines of the broiler are not able to absorb sufficient nutrients, resulting in deficiencies and growth retardation.

Certain REO strains cause MAS like symptoms. This does not mean that all MAS is caused by REO infections:

Any pathogen that disturbs the optimal balance in the intestinal flora, can cause symptoms of MAS.

In cases of MAS caused by REO infections, REO vaccination of the parent stock is the most effective way of prevention.

Are different strains of REO virus responsible for different symptoms or syndromes in the infected birds?Why do some inactivated vaccines contain different REO virus strains?

REO virus isolates have been associated with a great variety of symptoms.

This has enabled the categorization of REO-related infections into different syndromes such as:1. Viral arthritis (VA)2. Brittle bone syndrome3. Mas4. Runting/stunting syndrome 5. Helicopter disease.

The S1133 (Lvd-Heijden) strain is reported to be isolated from a case of VA.

The 1733 strain is isolated from a case of classic MAS. The 3005 from a case of brittle bone.

However, a REO isolate from one specific syndrome will not necessarily always cause similar symptoms.

Neither is it possible to differentiate various isolates by current serological methods: the REO antibodies do not make a distinction.

In fact, the immune system does not distinguish between the one and the other pathotype: antibodies induced by one isolate will protect equally against the other pathotypes.

Inclusion of isolates of two or more syndromes in a vaccine does not give a broader protection.

Moreover, it would be un-practical to include isolates of all syndromes, associated with REO virus infections.

However, including more antigen per dose can increase the immune response, measured in titers.

A higher titer sometimes can induce a more effective protection, which in itself could induce a higher titer and a better protection.