The situation of CBPP in Namibia in view of a new outbreak in the Caprivi region

O. J. B. Huebschle^[41], C. Bamhare^[42], and G. Tjipura-Zaire^[43]

Introduction

The history of contagious bovine pleuropneumonia (CBPP) in Namibia goes back to precolonial times when infected oxen from the Cape Colony carried the disease into the territory at the middle of the 19^th century. Though shortly contained after the first outbreak it made its reappearance after only a few years. Early attempts then to contain the disease by vaccination (Wilems) were only partially successful as a result of extensive cattle movement linked with cattle rustling. Further attempts during the early years of the 20^th century with a strong emphasis on movement control and vaccination and destruction of infected animals proved successful in eradication of CBPP in the commercial farmlands. However due to the nature of livestock rearing in the communal lands CBPP persisted until today despite many different vaccination campaigns during the last 80 years. According to official documents at least 5 different vaccine formulations have been used for disease control with varying degrees of success. Amongst these vaccines were the Kabete vaccine, the KH3J strain vaccine, the V₅ strain vaccine, the T1 SR vaccine and presently the T1 44 vaccine. Changes of vaccine formulations were brought about either due to serious side reactions or due to poor immune response as judged by failing protection. The latest vaccine change was done in 1997 after a period of no vaccination, which led to a considerable, renewed upsurge in clinical CBPP cases (Figure1, source: yearly reports).

Figure 1. Clinical/pathological diagnosis of CBPP in Northern Namibia 1995-1999)

As mentioned above, 1997 had a peak number of observed CBPP cases which decreased substantially after initiation of the T1 44 vaccination aimed to reach a near 80-90% vaccine coverage. However, due to civil strive still occurring along the northern border of Namibia, little control of cattle movement (transhumance) in these areas has been possible in the past. The movement of cattle from Angola still persists and veterinary services vaccinate all animals from Angola that are detected. Tables 1 and 2 show the number of confirmed and suspected cases of CBPP that have been diagnosed in the last few years.

Table 1. Confirmed and suspected CBPP cases 2000-2003* in Kavango Region.

Sera submitted to Laboratory for confirmation

* until end October 2003

Despite a recognisable reduction of clinical signs CBPP after the onset of vaccination during 1997, new cases albeit at a distinctly reduced rate have been recorded since the inception of the new vaccine strategy. Over the years the number of cases in traditionally known CBPP infected areas remained at a lower yet recognisable level. In all these cases it could be very often established that CBPP had been brought in via infected animals originating from beyond the northern border of Namibia. However, the areas affected remained restricted to the Kavango region the 4 North-central regions and the Kunene region. At no time since the end of the forties in the previous century had CBPP been recorded in the Caprivi region. This has been achieved by imposing strict movement control from the Kavango region to the further easterly-situated Caprivi region and further on by the fact that certain areas along the relatively narrow Caprivi Strip had been declared a cattle free zone. Both restrictions allowed curtailing an eventual spread of CBPP from the endemically infected Kavango region into the Caprivi region.

Table 2. Confirmed and suspected CBPP cases 2000-2003* in North Central Namibia

Sera submitted to Laboratory for confirmation

* until end October 2003

Despite a recognisable reduction of clinical signs CBPP after the onset of vaccination during 1997, new cases albeit at a distinctly reduced rate have been recorded since the inception of the new vaccine strategy. Over the years the number of cases in traditionally known CBPP infected areas remained at a lower yet recognisable level. In all these cases it could be very often established that CBPP had been brought in via infected animals originating from beyond the northern border of Namibia. However, the areas affected remained restricted to the Kavango region the 4 North-central regions and the Kunene region. At no time since the end of the forties in the previous century had CBPP been recorded in the Caprivi region. This has been achieved by imposing strict movement control from the Kavango region to the further easterly-situated Caprivi region and further on by the fact that certain areas along the relatively narrow Caprivi Strip had been declared a cattle free zone. Both restrictions allowed curtailing an eventual spread of CBPP from the endemically infected Kavango region into the Caprivi region.

It was only during August 2003 that state veterinarians communicated clinical observations suspicious of CBPP from an area in the Caprivi region, which is relatively remote from the Kavango border after the region remained free of CBPP since 1938 (Figure 2).

Figure2. Distribution of CFT titers of 141 sera in a new CBPP outbreak of the Caprivi region, Namibia, during 2003.

Post mortem examination and subsequent isolation of MmmSC during September 2003 confirmed the original suspicion. Further enquiries with the owner of the affected animals revealed the specific cattle owner made his living with cattle trading (speculation) and that he might well have brought in animals from Zambia, across the border. As the animal that was inspected at post mortem had advanced lesions it stood to reason that most animals in his herd had contracted CBPP by then. Therefore, all 106 animals in the specific herd were sampled and serum was subjected to a CF test. Seventy six animals in this group (72%) had serum titres ranging from 1:20 to ³ 1:640. The animals were then taken to a quarantine facility and slaughtered 3 weeks later. Inspection of carcasses revealed that 80% of them slaughtered had typical pathological lung lesions as seen in MmmSC diseased animals. During a visit to the affected areas another 36 sera from animals known to have been in close contact with the affected herd have been sampled. Of these animals 27 (75%) animals tested again positive in the CFT again with titres ranging from 1:10 to ³ 1:640.

Authorities have in the meantime instituted a vaccination programme for the area where CBPP has been detected in the Caprivi, as compulsory culling of animals could not be instituted due to financial constraints and serious objections of the animal owners.

It is noteworthy to have a new, affirmative look at the CFT system that in this very case definitely has passed another validation successfully. All animals in the area were for the first time infected and could distinctively be identified by means of the CF test as CBPP positive animals which was further corroborated by the detection of pathological lesions during post mortem inspection.