Diseases caused by Rickettsia and Mycoplasma spp

Diseases caused by Rickettsia and Mycoplasma spp.


Heartwater (Hydropericardium)

"Black dung" when affecting African cattle and buffalo


"Sheep fever" when seen in sheep

Heartwater is an acute, non contagious disease of cattle, sheep, goats, antelopes and wild ruminants. It is caused by the rickettsial organism Cowdria (Rickettsia) ruminantium.


Transmission:

Heartwater is transmitted by various species of Amblyomma ticks. Transstadial transmission of the organism occur in vector ticks.

Antemortem findings :


Peracute form

1. Incubation 14 – 28 days
2. Fever
3. Diarrhoea
4. Convulsions and death

Acute form

1. Fever up to 41.7°C
2. Rapid breathing
3. Lack of appetite, depression and listlessness

Nervous signs include

1. Twitching of the eyelids
2. Protrusion of the tongue
3. Champing of the jaw
4. Walking in circles
5. Paddling with legs in recumbent animals
6. Opisthotonos and convulsions

Postmortem findings :

1. Hydropericardium
2. Hydrothorax
3. Pulmonary edema and ascites
4. Haemorrhagic gastroenteritis
5. Enlarged liver, spleen and lymph nodes
6. Haemorrhage in the abomasum and intestine
7. Edema and haemorrhage of the brain

Judgement :


Carcass of an animal affected with heartwater is condemned in the acute stage of the disease. In a chronic case, the carcass may be approved if adequately bled and muscles are wholesome in colour and texture. The affected organs are condemned.


Differential diagnosis :



Peracute form of heartwater should be differentiated from anthrax. The acute nervous form of the disease is differentiated from tetanus, rabies, cerebral trypanosomiasis, strychnine poisoning, piroplasmosis, theileriosis, lead and organophosphate poisoning, parasitism, arsenical poisoning and poisoning with certain plants.





Fig. 63 : Heartwater Cowdria ruminantium in bovine brain smear (arrow).



Q fever (Queensland fever, Nine mile fever, American Q fever, Australian Q fever)


Q fever is a disease of cattle, sheep, goats, donkeys, camels, fowl, dogs, cats, pigeons and humans. It is caused by Coxiella burnetii. Q fever is an occupational disease of livestock personnel. farmers and laboratory personnel.

Transmission :

Ticks spread infection to cattle which develop mild disease. The faeces deposited on animal hide by ticks may be the source of infection for humans. Q fever is also transmitted by inhalation or dust contaminated with infected animal secreta or excreta. Healthy animals may serve as a carrier and shed the organism in milk, urine, faeces, placenta and fetal fluids. They harbour the infection and no clinical signs are observed. Contaminated meat and water are further means of infection read.

field cases there are no clinical signs of this disease. In the disease produced by the inoculation of cows via the udder the clinical signs may include:

1. Acute mastitis
2. Loss of appetite and depression
3. Serous nasal and lacrimal discharge
4. Difficult breathing
5. Atony of the rumen
6. Abortion in pregnant cows

No gross lesions are reported in cattle.

Discussions :
Coxiella burnetii is highly resistant and was isolated from farm soil 6 months after the removal of animals. It may persist in the udder up to 3 years. The temperatures of milk pasteurisation (in bulk at 63°C for 30 minutes or the common method at 72°C for 15 seconds) kill this agent in milk. Vaccination will reduce shedding of organisms in milk.

This disease in humans has a sudden onset and is characterized by loss of appetite, weakness and generalized malaise lasting from 1 – 2 weeks. Pneumonia may also be present. Death may be caused by endocarditis in older people. More severe symptoms of Q fever are noticed.

Contagious bovine pleuropneumonia

This is an acute, subacute or chronic highly infectious disease of cattle caused by Mycoplasma mycoides var, mycoides.

Transmission :


Aerosol and droplet infection from the infected animals. The recovered animal called "lungers" act as carriers and shedders, especially under stress.


Antemortem findings :

1. Incubation: acute 10 – 14 days, chronic 3 – 6 months
2. Morbidity: 90 % in susceptible cattle
3. Mortality: 10 – 50 %
4. Fever
5. Depression
6. Lack of appetite and loss of weight
7. Coughing on exercise
8. Shallow rapid respiration, grunting and gurgling
9. Extended neck, lowered head and open mouth
10. Arched back and outward rotated elbow
11. Arthritis in young animals

Postmortem findings :

1. Fibrinous inflammation of the pleura (pleuritis)
2. Straw coloured fluid in the thorax (Fig. 64)
3. Lobar pneumonia with red hepatization, marbled appearance of lung lobules (Fig. 65) due to thickening of interlobular septae and interlobular pulmonary edema
4. Enlarged mediastinal lymph nodes
5. Walled-off sequestra formation in chronic cases
6. Haemorrhage in the heart
7. Arthritis and tenosynovitis

Judgement :

Carcass of an animal affected with contagious bovine pleuropneumonia is condemned if the disease is associated with fever, inadequate bleeding of carcass, serous infiltration of the brisket and emaciation. Recovered animals showing no generalized signs of the disease are approved and the affected organs are condemned.

Differential diagnosis :



Shipping fever (Pasteurellosis). East coast fever, foreign body pneumonia, IBR, tuberculosis, chlamidial infections and lungworms




Fig. 64: Contagious bovine pleuropneumonia. Straw coloured fluid in the thorax and partial lung hepatization.






Fig. 65: Contagious bovine pleuropneumonia. Lobar pneumonia with red hepatization and marbled appearnce of lung lobules