Pasteurellosis, Biology

Pasteurellosis


Haemorrhagic septicaemia (HS) Synonym    :    Gal Ghotu
Causative organism B:2                              :    Pasteurella multocida Serotype
Haemorrhage septicaemia (HS) is a form of acute pasteurellosis in cattle and buffaloes. The disease is widely prevalent in India among cattle and buffaloes, and  occurs mostly in acute septicaemic form. In recent outbreaks, a mild form with lower mortality has been observed. It occurs generally in low lying humid areas and is often seasonal. Outbreaks occur during the periods of highest humidity such as during monsoons.


The HS is mainly caused by P. multocida serotype B:2 as reported from other parts of South-East Asia, though other capsular types also play a some role. P. multocida is a small, non-motile, non-sporing, capsulated gram-negative cocco-bacillus. In blood smears and oedema fluid smears, when stained by Leishman stain, it has a characteristic bipolar appearance. It has a low resistance to heat and sunlight.


The organisms may be normal inhabitants especially in the respiratory tract (oropharyngeal area). Stress due to exhaustion because of excessive work, starvation, chilling or change of diet may precipitate the disease. Fatigue from rail or road journey may also predispose animals to infection.


Transmission:
HS is carried by the carrier animals season after season. The organisms are maintained by the carriers during the interepidemic period. The organisms are present as commensals in the respiratory tracts of apparently healthy animals, and from there spread to susceptible in-contact animals, either by droplet inhalation or by ingestion. Under certain circumstances the organisms in clinically healthy animals increase their rate of growth and produce a severe or fatal infection. The predisposing factors are

(i) stress and environment, particularly during rainy season in tropics

(ii) confinement or transport of cattle

(iii) vaccination against other diseases

(iv) as concurrent virus infections.

The rapid multiplication of organisms in respiratory tract gives rise to infected droplets which are exhaled in air and are source of infection for other animals.The sick animals also contaminate the atmosphere by excreting a large number of bacteria in faeces. According to one view, the virulence of P. multocida increases by rapid passage through a number of animals as subsequent cases are usually much more acute than earlier ones in an outbreak. Nevertheless, fully virulent pasteurellae can be recovered from apparently healthy animals before an outbreak occurs. This according to the second view, obviates the necessity to postulate the increase of virulence of carrier strains for initiation of the disease. The transmission of organisms from the resistant carrier to the in-contact animal with lowered resistance results in disease condition. The resistance of cattle already stressed due to debilitating effects of long summer drought, falls considerably at the onset of monsoon due to sudden exposure of inclement weather. Hot humid weather optimal for the multiplication and spread of microbes, and consistent with the general fall in the resistance of susceptible population results in ideal conditions for the disease to assume an outbreak.


Symptoms: large number of cases in domestic buffaloes and cattle are acute or even peracute. There is a very short incubation period of about 2 days followed by high fever, anorexia, depression, increased respiration, marked salivation and acute conjunctivitis. The visible mucous membranes become dark red and infected.In the peracute form, there is a marked oedema, resulting in hot and painful inflammatory swelling in the head and neck region. The tongue protrudes and is dark  red. The throat lesion brings about respiratory distress and sometimes suffocation; the disease is appropriately called Galghotu in Hindi. Death usually occurs within a few hours.


In less rapid form, the alimentary tract is involved and haemorrhagic diarrhoea is seen. The lungs may be affected with bronchopneumonia resulting in respiratory distress, cough and laboured breathing. The animals usually die within a few hours or lingers for 3 to 4 days. Recovery from true haemorrhagic septicaemia is rare, particularly in buffaloes. The rate of mortality ranges from 70% to 100%.


Lesions: In the peracute form, the oedematous swellings of the neck and head region are blood stained. Extensive petechiae are observed on the serous membranes and internal organs. There is oedema of lymph nodes and of lungs which show red and grey labour inflammation and thickened septa. In case of involvement of the alimentary tract, there is a extensive gastro-enteritis, the gut contents being fluid and blood-stained. Apart from occasional small haemorrhage the spleen in unchanged. The abdominal pleural and pericardial cavities contain large quantities of blood-stained fluid. Sub- serous haemorrhage in the endocardium, especially of the left ventricle, is almost diagnostic of this disease.


Diagnosis: An outbreak of haemorrhagic septicaemia is easily identified, but individual cases may be more difficult. The rapid course of the disease together with throat swelling is distinct characteristics. The normal size of the spleen will distinguish it from anthrax. In the majority of cases a reasonably accurate diagnosis is not difficult when the history of the disease in the locality, the environment and the season are taken into consideration.


Blood smears (peripheral or heart blood):
stained by Leishmans stain would reveal the characteristic biploar organims; heart blood swabs, oedema fluid swabs on scarification in rabbits leads to death with the pathognomonic lesion of haemorrhagic tracheitis. Cultural examination of the heart blood swab would reveal the characteristic organisms.Pieces of spleen taken aseptically in suitable containers are also useful for diagnosis. Where necropsy is delayed for some time after death, long bones (e.g. tibia and femur) taken out intact, should be forwarded to the laboratory for detailed examination as the pasteurellae survive for a longer period in long bones. Long bones can also be used for PCR.


Treatment: Treatment can be effective if it is carried out in the early stages of the disease but the rapidity of the disease often prevents this. Sulphadimidine has been recommended but recent isolates have shown increased resistant to the drug. The broad spectrum antibiotics are effective.


Control:
In the endemic area, prophylactic vaccination should be carried out annually about a month before the onset of rains. Oil adjuvant vaccine protects animals against the attack of the disease for about 1 year, whereas alum-precipitated vaccine and broth vaccine afford protection for about 5 and 2 months, respectively. Unexpected outbreaks can be handled by prompt vaccination coupled with chemotherapy, if necessary. In these circumstances, oil adjuvant vaccines should be used in conjunction  with a small simultaneous dose of broth vaccine to advance the onset of effective immunity, since the development of immunity with oil adjuvant vaccine takes about 2 weeks. Prior to the establishment of protective immunity healthy animals should be segregated from the sick and in-contact animals.


Pasteurellosis in other animals: The causal organism Pasteurella multocida is responsible for a number of diseases in other animals called as pasteurellosis.

Posted Date: 9/17/2012 7:11:05 AM | Location : United States







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