Epizootiology of camel contagious ecthyma in Eastern Sudan

It consists of the Butana plains which lie between the main Nile, the Blue Nile and the Atbara River (Eastern part of Sudan). Areas South and South-West of Kassala as well as East of the Atbara River were also included in the survey (figure 1). Camel herds originating from the Blue Nile area were investigated as well at Central Butana during the rainy seasons. Trees commonly found in the study area consisted of Acacia mellifera, A. nubica and A. nilotica (1). In addition, the Blue Nile has the following species: A. laeta, A. albida and A. polyacantha (6). Acacia tree distribution in the Sudan is shown in figure 2.

season (November-June), some of them move southward up to Doka area, 350 km South of Kassala, few migrate northward up to Gash Delta and others cross over to the Red Sea toast around Sawakin and Toker (400 km North East of Kassala) to take advantage of range developing as a result of the winter rains (1). The Shukriya, Lahawiyin, Bawadra and Mussalamiya stay in Butana in the rainy season and move during the dry season towards the Atbara River basin. A significant proportion of these tribes as well as some of Rashaida coordinate their movements to coincide with the harvest season (January-March) thus using the trop residues in the rain-fed agricultural schemes of Gedaref area (1). Ruffaa, Kawahla and Arakiyin tribes of the Blue Nile area spend the dry season at rain-fed agricultural schemes in the area and move to the North towards Butana plains in the rainy season to use free range pasture.
The came1 population in the study area has been estimated at 750,000, which represents 20% of a11 Sudan camels (13).
Fifteen came1 herds were visited monthly between March 1992 and June 1993 in connection with the French-Sudanese Came1 Research Project. The aim of this project was to study the husbandry and production parameters of camels in Butana area (1). During each visit to the study area additional 15 to 20 herds, which were not covered by the above mentioned project, were also investigated. sex of the affected animals were collected. Herders' accounts of the disease history and progress of symptoms were also obtained. Skin biopsies or scabs were collected from affected animals for laboratory confirmation of preliminary tentative diagnosis.

Luboratory investigation
Ten percent suspensions were prepared from skin biopsies or scabs in phosphate buffered saline (PBS). After light centrifugation one drop of each sample was placed onto a separate carbon-coated grid. After staining with 2% phosphotungestic acid the grids were dried and examined by electron microscopy.

CCE clinical features
Initially small nodules appeared on the lips of affected animals followed in most cases with swelling of the, face and sometimes the neck (figure 3). Affected animals were ataxic and off-food. Papules and vesicles appeared later and within a few days developed into thick scabs and fissured trusts ( figure 4). Lesions occurred sometimes on the face, eyes and nares and in severe cases in the gingiva, dental pad and tongue.'Death was probably due to starvation caused by the inability of affected animals to graze or suckle their dams. Healing occurred within 20-30 days in most cases, but sometimes the course of the disease extended up to three months.

Disease incidence
A number of 305 came1 herds were surveyed for CCE occurrence. This number represented approximately 3% of the whole came1 herds in the study area. Thirty-eight herds were found tolbe Epizootiologie de l'ecthyma contagien du dromadaire au Soudan  affected with the disease (herd incidence rate in the sample: 12.5%). The disease was recorded in 35 of these herds (92.1%) during the rainy season (July-October) and only 3 affected herds (7.9%) were recorded in the winter season (November-March), while no disease outbreak was seen in the sumrner season (April-June). Table 1 shows the morbidity and mortality rates and the fatality case rate of camels affected with CCE in Central Butana and Kassala, Southern Butana and the River Atbara, and the Blue Nile areas. The mean morbidity rate in came1 calves less than one year old in the three geographical areas was 60.2% and the mean mortality rate was 8.8%, while the mean fatality case rate was 13%.

Age and sex distribution
The age distribution of 280 CCE cases with 34 deaths is shown in table II. Al1 cases occurred in Young animals up to 3 years old.
Most of the affected animals (70.7%) were in the age group 7-12 months and 27.2% of cases occurred in animals agcd O-6 months. Four animals (1.4%) aged l-2 years and 2 animals (0.7%) aged 2-3 years accounted for 2% only of the affected animals. The fatality case rate was higher in the age group O-6 months (21%) than in that 7-12 months (9%).
Sex distribution of CCE 274 cases revealed a malelfemale ratio of 111.2.

n DISCUSSION
The CCE outbreaks reported in the present study occurred in several came1 herds belonging to different tribes and involving different breeds of camels. The observed clinical symptoms of the disease compared well with those described previously (3,5,8,11). The total morbidity rate was found to be 10% while the mean morbidity and mortality rates in the susceptible age group (came1 calves less than one year old) were 60.2% and 8.8%, respectively. Most camels in the study area fed during the dry season on harvest remains (Sorghum stalks) of the rain-fed agricultural schemes. During the rainy season animals fed mainly on free range pasttire in Butana plains. However, early in the rainy season (June-July) and due to the spoiling effect of the rains on the Sorghum stalks camels were obliged to leave these schemes and browse Acacia trees in the area until adequate green grasses developed in Butana plains. At that time of the year CCE outbreaks occurred. A factor responsible for this seasonality could be lip skin abrasion resulting from eating thorny Acacia trees at this time of the year when no other source of food was available. BuEhnev et ul. (3) were of the same opinion when they argued that the thorny plants damaged the lips allowing transmission of the parapox virus. TO gain more data on the pattern of CCE outbreaks the study area was revisited during the rainy seasons of the years 1993 and 1994. The disease pattem was similar to that observed in 1992. It seems that CCE constantly appears every year during the rainy season affecting Young came1 calves in their first autumn season of grazing and also older animals which escaped previous exposure to the virus.
The occurrence of the disease was lower (24%) in the age group O-6 months than in that of 7-12 months (62.8%). This may be due to the passive transfer of immunity which seems to disappear after 6 months.
In the present study CCE incidence and severity varied depending on the location. The morbidity and mortality rates were relatively high in camels from the Blue Nile area compared to those from Central and Southern Butana, Kassala or the Atbara River (  (7).
Seasonal movements of camels had a significant role in the spread of CCE in the study area. The authors observed that outbreaks of the disease tended to first appear at the start of the rainy season (June) in the Blue Nile and Southern Butana areas and the infection extended northward coinciding with the annual movements of camels towards Butana plains. However, bearing in mind the meteorological data on the direction of seasonal winds the possible involvement of insect transmission cannot be excluded. This is not unexpected since insects have been suspected or reported to be responsible for transmission of other members of the Poxviridae such as the lumpy skin disease virus (16), sheep pox (9), fowl pox (14), swine pox virus and myxomatosis virus (15). More detailed epizootiological studies involving historical analysis at the animal level are much needed in order to complete the picture.
From the findings of the present study it appears that the major factors associated with increased likelihood of CCE occurrence are: season of the year, camel age, camel movements and location and their association with thorny Acacia trees.
Special attention should be directed towards introducing measures to control this disease in the Sudan particularly in the Blue Nile area. In the absence of an effective vaccine against CCE control measures must include quarantine of infected areas, proper disposal of carcasses and all contaminated materials, management of camel movements, as well as provision of extension services to camel herders. Care should be taken to avoid skin abrasions by provision of soft food to young camels when possible.
In conclusion, this poorly studied disease which represents an endemic problem in the Sudan needs to be looked into seriously due to its high contagiousness, significant mortality rate and other economic impact on the growth rate and milk production as a result of calf mortality.  Herd prevalence of CCE significant depending on the location ; χ 2 with 2 degrees of freedom; p = 0.006 Animal prevalence of CCE significant depending on the age (less than one year) ; χ 2 Yates corrected with two degrees of freedom ; p < 0,0001 Animal prevalence of CCE significant depending on the age (less than one year) and stratified on the three locations. Mantel Haenszel Summary χ 2 ; p < 0.0001 (Assumption: herd structure is similar in the three areas) Se llevó a cabo una encuesta sobre los dromedarios criados en libertad en las regiones de Butana, Kassala y el Nilo Azul, en Sudán, entre 1992 y 1994, con el fin de evaluar la incidencia del ectima contagioso del dromedario (ECD). Se encontraron treinta y ocho hatos afectados con la enfermedad. Desde un punto de vista clínico, las lesiones aparecieron primero sobre los labios de los animales afectados, bajo forma de costras o de costras fisuradas. Todos los casos de ECD concernieron dromedarios jóvenes, hasta la edad de 3 años, con 97,8% de ellos de menos de un año. Las tasas de morbilidad y de mortalidad medias en los jóvenes de menos de un año fueron respectivamente de 60,2 y de 8,8%, mientras que la letalidad media fue de 13%. La enfermedad varió segun la estación y estuvo asociada con la estación lluviosa y la alimentación con acacias espinozas, causando lesiones de la piel.