Dr Rick Last – BVSc; M.Med.Vet (Pathology)
Specialist Veterinary Pathologist
Vetdiagnostix – Veterinary Pathology Services
We received a range of diagnostic samples from an outbreak of acute mortalities in a group of beef weaners from the Estcourt Area, Kwazulu-Natal. The presenting clinical signs were sudden onset facial swelling with subcutaneous and submandibular oedema with extensive subcutaneous hemorrhage and myositis over the face and neck. The referring veterinarian initially suspected a clostridial myositis “malignant oedema” syndrome. The clinical duration of disease was short (<48 hours) with high mortality rate and poor response to therapy.
Included in the samples submitted was the whole head of one weaner for examination. Gross dissection of the head revealed
- Severe necrotizing facial myositis and cellulitis of particularly the left side of the face (Figures 1 and 2)
- Severe intermanbdibular cellulitis and oedema (Figure 3)
- Myositis of sternocephalicus muscle plus pharyngeal cellulitis with hemorrhagic lymphadenitis of the retropharyngeal lymphnode (Figure 4).
Lung, liver and small intestine were submitted on ice from another weaner that had died, while sub-orbital muscle, sub-mandibular muscle and lymph node were collected from the head. All of these tissues were set up on both aerobic and anaerobic cultures and muscle impression smears were collected for Clostridial Fluorescent Antibody Staining.
Aerobic cultures produced a heavy growth of Pasteurella multocida from all fresh tissues submitted. On anaerobic culture no Clostridia were isolated and Clostridial FAT was negative for Clostridium chauvoei, C. novyi, C. septicum and C. sordelli.
Retropharyngeal lymphnode histology revealed a severe locally extensive, fibrinopurulent necrotizing, lymphadenitis with widespread hemorrhage, fibrinocellular vascular thrombosis and multiple large bacterial emboli composed of a uniform population of small bipolar organisms resembling Pasteurella sp. Histology of the facial muscles was characterized by severe diffuse acute hyaline degeneration and necrosis with myofibre cytolysis. Severe interstitial purulent myositis with degenerate neutrophils and fibrinocellular thrombosis. Multiple colonies of a uniform population of bacteria resembling Pasteurella sp identified scattered through the section.
The Pasteurella multocida isolates were submitted to the Bacteriology Section of the Onderstepoort Veterinary Institute for serotyping and these isolates were typed as Pasteurella multocida Serotype B.
Based on all of the above findings a diagnosis of hemorrhagic septicaemia (peracute oedematous form) was made.
Pasteurella multocida is divided into 5 capsular types, A, B, D, E and F. Cattle and sheep in South Africa are usually affected by either types A or D. These two serotypes are associated with the usual respiratory disease syndrome in ruminants. Pasteurella multocida types B and E are associated with haemorrhagic septicaemia, a peracute to acute, highly fatal bacterial disease, primarily of cattle and to a lesser degree in African buffalo, water buffalo, sheep, bison and camels. Until the 1990’s, type B was found in Asia, and type E in Africa, with Egypt being the exception at the bridge between the continents, which was infected with both B and E. They are described as types B:2 or E:2.
Historically South Africa has generally been free of haemorrhagic septicaemia, with only a few sporadic cases of type E reported, usually in areas bordering neighbouring African countries. During the late 1990’s and early 2000’s, cases of haemorrhagic septicaemia due to type B:2 were found in Namibia and Zimbabwe. South Africa has then remained free of type B, until 2011, when type B was detected in African buffalo.
Outbreaks are more common during rainy seasons with bacteria being maintained in intervening periods in the nasopharyngeal areas of carrier animals. Outbreaks are associated with stress induced recrudescent infections in carrier animals with extensive proliferation and dissemination of the bacteria to susceptible in contact animals.
In the majority of cases hemorrhagic septicaemia presents as a peracute disease with many animals dying without exhibiting clinical signs. Less fulminant infections are associated with pyrexia, prostration and excessive drooling and in these animals where clinical signs are noted, mortality rates are virtually 100%, even with antibiotic therapy. Massive bacterial proliferation with endotoxin production is likely central as the cause of death. Pathology in this form of the disease is usually characterized by fibrinohemorrhagic interstitial pneumonia, hemorrhagic lymphadenitis and gastroenteritis with widespread serosal hemorrhages and fluid exudation.
There is an acute / peracute oedematous form of hemorrhagic septicaemia characterized by severe facial oedema and cellulitis, particularly of the throat area. There may also be involvement of the whole head, tongue, brisket or a limb. Oedema fluid characterized by copious clotted, straw coloured exudates. Such a syndrome was documented in these cases.