Epidemiology of contagious bovine pleuropneumonia (CBPP) in Northern states of Nigeria. An update

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Introduction
Contagious bovine pleuropneumonia (CBPP) is caused by Mycoplasma mycoides var. rnycoides (15) and is characterised by marked oedema of interstitial tissues in the lung, diffuse pneumonia and serofibrinous pleuritis (1). It plagued cattle in Europe and elsewhere in the 19th century as well as in Africa at the present time (1, 4, 6, 22).

Contagious
bovine pleuropneumonia has occurred in Northern Nigeria for many years, causing generally high morbidity and mortality. Annual reports show a fluctuating number of outbreaks from time to time especially among the trade cattle (1,12,22).
The results of efforts to control CBPP are fluctuating. Reports show that the disease was controlled by 1965, but unfortunately it re-emerged (16). An attempt towards a regional international campaign for eradication of CBPP in West and Central Africa started in 1969. Nigeria launched the joint project (JP28) in 1974, although the actual campaign started in 1971 (6). When vaccination increased, the number of outbreaks decreased. At present, there is an upsurge of the disease across the country. The aim of this short communication is to reveal the outbreak pattern, the relationship between outbreaks and vaccination coverage, seasonal distribution pattern and geographical location of the outbreak in relation to the disease situation in the frontier countries.

Materials and Methods
Data on CBPP outbreaks and vaccination figures in Nigeria for a twenty-year period (1970-l 989) were collected from disease outbreak report files in Epidemiology, and National Rinderpest/CBPP CO-ordination Units of the Federal Livestock Department, Kaduna. They were plotted against the respective years to determine the relationship between vaccination campaign and incidence of CBPP in Nigeria. Data on monthly outbreaks for Kaduna, Kano and Sokoto from 1984-1986, were also collected from the same source and monthly variation for the reported outbreaks determined using the ratio-to-moving average method (13).
Other data collected include general outbreaks information in ten Northern states between 1985 and 1989.
Finally, information on CBPP situation in the neighbouring countries with respect to their control policies and results were collected with relationship to our control problems. Table I shows that the number of outbreaks is increasing since 1986. The number of doses of vaccine used is decreasing.

Results
The relationship between the vaccination campaign and the number of outbreaks is shown in figure  1. When the vaccination was intensified between 1975 and 1986, the number of outbreaks was Iow. Also on the increase in late 1980s were the number of affected herds and the total number of deaths recorded in the affected herds. Analysis of three-year data from Kaduna, Kano and' Sokoto on a monthly basis revealed that most of the out-~ breaks occurred between October and March (table Il). Time series decomposition of the data revealed a similar~ pattern ( fig. 2). When outbreaks between 1985 and 1989 were plotted in a map using the map references indicated in the outbreak files, it was observed that outbreaks tended to concentrate along river banks. Highly noticeable was the concentration of cases along river Benue in the Gongola State, river Sokoto, river Niger and river Hadeija (map 1). These sites also happen to be dryseason grazing grounds.
The control policies in the studied frontier countries (Cameroon, Niger and Chad) were similar to those of Nigeria, but the results obtained varied. In Cameroon, though the situation was improved, it still remains precarious due to limited national resources and infiltration of "lungers" from endemic neighbouring countries ; while Niger recorded another outbreak in 1990 after six years of freedom from the disease, Chad has not reported any outbreak of the disease since 1988 (8, 9).

Discussion
Results of the vaccination campaign and the outbreaks observed in this study further strengthen the view that intensified efforts towards effective vaccination contribute to lowering CBPP outbreaks (1, 4, 7, 21). The pattern of the graph ( fig. 1) is an indication of the achievements of JP28, but unfortunately the rhythm of vaccination appeared to decline towards the late 1980s. This may be due to an inadequate availability of CBPP vaccine or to the fact that herdsmen refused vaccination of their cattle for fear of either adverse post-vaccinal reactions or cattle tax (4).
The results of monthly variation and time series decomposition agreed with the reports of other scientists (1,5,12,22) according to which the period of the largest number of outbreaks corresponded to the time of the greatest cattle concentration towards the rivers for dry-season grazing and watering. The close contacts among healthy and carrier animals along these river for banks probably enhanced the transmission of the infection.

Conclusion
The variation in the outbreaks from state to state agreed with the reports of DAVID-WEST (7) and ANISULOWO (4) according to which the extent of outbreaks of CBPP within a patticular location depends on the availability of adequate and effective control measures or repot-ting efficiency in that area. But the outbreaks recorded may not reflect the actual situation of the disease as many cases may not have been reported. Therefore there is need to intensify efforts towards cattle movement across borders as well as vaccination in order to control the increase in the number of outbreaks. TO reach a large number of animals, vaccination could be carried out along river banks and other dry-season grazing areas during the dry season.  (1970)(1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989) are plotted against the respective years to determine the relationship between the vaccination and number of oubreaks recorded in Nigeria. The result indicates that when vaccination w-as intensified between 1975 and 1986, the number of outbreaks were low. The number of affected herds and the total number of deaths recorded increased in the late 1980s. Data on the seasonal distribution of outbreaks showed that they mostly occurred during the dry season (October-March).
When data collected on geographical locations were plotted in a map using the same references indicated in the outbreak files, it was observed that they tended to concentrate along river banks. Also' the disease situation in the neighbouring countries was related to our own control problems.