Bovine Petechial Fever

Bovine Petechial Fever

Common names: Ondiri disease

Description: Tick borne cattle disease

Introduction

Bovine Petechial Fever is a cattle disease, characterised by haemorrhages, fever, oedema, and abortion in pregnant animals. The cause is an organism called Ehrlichia ondiri because the disease was first identified at Ondiri, near Kikuyu, on the outskirts of Nairobi. To date the disease has only been confirmed in the highlands of Kenya at altitudes of over 1500m (5000 feet), although it is considered likely to occur in neighbouring countries with a similar geographical features. Suspected cases have occurred in the isolated highlands of eastern Tanzania.

Mode of spread

It is not known how the disease is transmitted, but a tick of restricted distribution is suspected. 

The organism is believed to be endemic in wild ruminants, particularly reedbuck and bushbuck, and it sporadically spills over into domestic cattle grazing in or at the edge of forest or scrub where these animals live. The disease is restricted to scrub or forest edges which have heavy shade, a thick layer and a high relative humidity. 

It occurs sporadically throughout the year in exotic cattle. Indigenous cattle appear to undergo infections that are not visible. Bushbuck and indigenous local cattle are proven natural hosts. 

Signs of Bovine Petechial Fever

Illness has not been reported in the true natural host, the bushbuck. The incubation period in cattle following natural exposure is believed to be 5 to 14 days. 

Reactions in recently imported cattle are very severe. They include:

• Sudden high fever 
• Abrupt drop of milk yield 
• Numerous petechiae (small red spots caused by bleeding from broken capillary blood vessels) on the mucous membranes of the eye, the inside of the vulva, and the lower surface of the tongue 
• Fluid accumulation in the lungs (Pulmonary oedema) 
• Death within 3 days. 

The severe form of the disease lasts longer. Signs include:

• A fluctuating fever 
• Drop in milk yield 
• Dullness in affected animals 
• Pregnant cows abort, most likely due to the high fever. 
• 24 - 72 hours after the onset of fever petechiae are seen, which fade within hours to be replaced by fresh petechiae, the cycles continuing for 7 -10 days. 
• Often the nasal discharges are blood-stained and the dung is black, tarry and blood-stained. 
• Sometimes one eye protrudes, the conjunctivae (the mucous membrane that lines the inner surface of the eyelid and the exposed surface of the eyeball) are swollen, the eyelids are turned outward, the eyeball is tense and the aqueous humor (the clear, watery fluid that fills the chamber of the eye between the cornea and the lens) is displaced by blood. This is the so-called poached egg eye. 
• Up to 50% of affected animals will die. 

Less severe infections show few signs apart from loss of condition and anaemia.

Diagnosis

The history, clinical signs, geographic location and post mortem finding should assist reaching a diagnosis. Post-mortem will reveal the presence of widespread ruptured blood vessels and oedema (accumulation of excessive amount of fluid). Haemorrhages are usually very marked in the mucosa of the urinary bladder and throughout the length of the alimentary tract and in the heart. The carcase is usually in good condition.  Lymph nodes are usually enlarged. The spleen may or may not be enlarged. 

For full confirmation a veterinarian will examine a blood or spleen smear to detect the organism Ehrlichia ondiri.

The disease must be differentiated from other haemorrhagic diseases such as Rift Valley Fever, Haemorrhagic Trypanasoma vivax infections, acute ECF, Heartwater, bracken poisoning, and Haemorrhagic Septicaemia. Hence the need when symptoms first occur to seek the assistance of a veterinarian.

Prevention - Control - Treatment

Prevention and control

• Separate cattle from areas frequented by bushbuck and reedbuck 
• Keep cattle away from forest edges 
• Isolate any animal showing sudden fever with a drop in milk yield 
• Examination of blood smears by a qualified veterinarian 

In recent years, incidences of Bovine Petechial Fever have declined because extensive development of farmland has cleared and eliminated bushbuck and reedbuck habitat.

Treatment

Tetracyclines are the drugs of choice. Double doses are required in the presence of symptoms. If given during the incubation period normal doses are enough. 

Most recovered animals become carriers and relapses may occur. Resistance to re-infection continues for up to 2 years following recovery.