Chronic Respiratory Disease

Master Preventive Medicine – Notes, Case Studies and Practical Insights – with Lomash

Chronic Respiratory Disease:

Synonym: CRD, Mycoplasmosis

CRD is chronic, slow spreading contagious disease in birds
It is characterized by obstinate hacking cough, sneezing and tracheal rales.
Disease is not a great killer but of great economic importance. Affected birds lays less egg than healthy birds.
Morbidity is typically high but mortality is low in affected flocks.
Sometimes coli infection complicates disease and this complicated form is now known as CCRD (Complicated Chronic Respiratory Disease).

Etiology:

Mycoplasma gallisepticum
Minute, coccoid filtrable organism measuring 0.5µ om diameter.
This organism donot grow in regular laboratory media. It requires special PPLO media for growth.
Ideal temperature for growth of mycoplasma is 37-38°C. colony appears as small nipples or dense area followed by thinning at the periphery.
Organism can be killed by commonly used disinfectants. Formalin can be used for disinfection of the farm.

Epidemiology:

Disease is distributed globally. Disease occurs in endemic form in most of the poultry farms in India.
A seroprevalence of 42.5% has been recorded from UP, India.
In a study conducted at CVL registry, CCRD has fourth highest greatest incidence among poultry disease in Nepal. Out of 2271 cases registered, 196 cases were diagnosed as CCRD, i.e. 9%.
Disease affects chickens and turkeys naturally.
Disease usually has high morbidity and low mortality in poultry flocks. In laying birds, it causes decreased egg production.
Disease is usually complicated by other infectious disease. Most common agent is E. coli followed by IB, Ranikhet disease.
Stress induces disease more frequently such as cold stress, vaccination with live virus, poor ventilation.
Disease mostly affects younger birds more severely than adult birds.
In broiler, most outbreaks occur between 4-8 weeks of age. Disease is more severe during winter.

Transmission:

Vertical transmission occurs through infected eggs.
Infection spread through droplet infection or inhalation of organism.
Nasal discharge is important source of disease transmission.
Wind also plays important role in transmitting the infection.
Infection also spread through direct contact with infected birds.
People are also important carriers of disease. About 60% cross-contamination between poultry farm is due to transportation by people on clothing and equipment.

Pathogenesis:

Clinical Findings:

Most characteristic symptoms are abnormal respiratory sounds, nasal discharge, sneezing, coughing, and breathing through open beak.
Decrease in feed consumption
Decreased in body weight

In laying flocks, egg production decreases.
Young birds show conjunctivitis with lacrimation.
Signs of ataxia and lameness accompanied with enlargement of hock joint may appear in some birds.

PM Findings:

Exudates are found in nasal passage, trachea, bronchi and airsacs.
Airsacs usually contains cheese-like inflammatory material.
Some degree of pneumonia may be seen.
In severe cases of complication with E. coli, there is pericarditis, perihepatitis and massive air sacculitis.
Rare cases of tenosynovitis and arthritis may be seen.

Diagnosis:

Differential Diagnosis:

It usually complicates CRD
Air sacculitis is more evident in case of mixed infection.
Pericarditis and perihepatitis are characteristic findings in case of colibacillosis.

Treatment:

Mycoplasma is susceptible to several antibiotics. These includes streptomycin, oxytetracycline, kanamycin, neomycin, gentamicin, tylosin, erythromycin, spiramycin, lincomycin.
Tylosin tartrate is drug of choice for CRD. It is given @ 25–50 mg/kg body weight orally in drinking water for 3–5 days or 3-5 mg/lb b.wt. SC
Oxytetracycline can be given in drinking water or feed @10-20 mg/kg for 5-7 days.
Enrofloxacin @10mg/kg, is effective for both mycoplasma and E. coli.
Supportive therapy such as vitamin A, D, E and C are given to improve immunity.
Electrolytes are provided in drinking water to reduce stress.
Liver tonics and probiotics are given to support liver and gut health.
Egg is treated with tylosin or gentamicin solution before incubation to remove vertical transmission of disease.

Control Measures:

Treatment donot completely remove the infection in flock, however it reduces mortality, signs and losses.
Best method to control disease is removal of infection from flock.
Chicken flocks or breeder stock should be free from M. gallisepticum. They should be screened for infection periodically.
Ventilation in poultry houses should be removed and ammonia levels should be maintained <25 ppm.
In case of outbreak, stocking density of fowl should be reduced.
Litter should be changed periodically. Wet litter should be removed from house and replaced by clean, dry litter.
Chronically affected birds should be culled and disposed of properly to limit spread.
Birds should be reared in all in and all out system.
Movement of people should be restricted within farm.
Water and feeder used in poultry feeding should be cleaned periodically.
Vaccination of breeder and layer in endemic areas. Live vaccine are administered to healthy birds at least 3-4 weeks before production starts. F- strain vaccine are used in broiler through eye drop or aerosol at 10 days of age.