In this study, antibodies against MAP have been demonstrated by ELISA in 7 out of 37 dairy herds tested in Khartoum State with an overall herd prevalence of 18.9% and animal level prevalence of 6.3%. Three of the positive herds were in Omdurman, which also had the highest prevalence at the animal level (33.3%); two positive herds were found in each of the other two localities. Summary of the results are presented in Table 1. As the maximum sensitivity of ELISA is about 50%, the true estimation of seroprevalence could be higher than the obtained results. However, ELISA positive animals may or may not be MAP shedders, but precautions should be taken to minimize transmission of infection within the herd.
Table 1
Prevalence of MAP antibodies in dairy cattle in Khartoum State
Area | Animal level | Herd level |
Breed | Total |
Local | Cross |
No. Tested | + ve | No. Tested | + ve | No. Tested | + ve | No. Tested | + ve |
No. | % | No. | % | No. | % | No. | % |
Khartoum | 7 | 0 | 0 | 44 | 2 | 3.9 | 51 | 2 | 3.9 | 11 | 2 | 18.2 |
Khartoum North | 0 | 0 | 0 | 78 | 4 | 5.1 | 78 | 4 | 5.1 | 15 | 2 | 13.3 |
Omdurman | 0 | 0 | 0 | 45 | 5 | 11.1 | 45 | 5 | 11.1 | 9 | 3 | 22.2 |
Total | 7 | 0 | 0 | 168 | 11 | 6.3 | 175 | 11 | 6.3 | 37 | 6 | 17.1 |
All seropositive animals were cross-bred females of good body condition, most (> 90%) of them were above three years old and > 50% were from medium herd size (50–100 head). The chronic nature of MAP infection and the long incubation period render the infected animals apparently healthy for years before showing overt symptoms of the disease [25] which interpret our findings. The numbers of local cattle in the farms investigated was small and none of the tested animals was seropositive. Local breeds are poor milkers compared to exotic breeds or their crosses and. therefore, limited numbers of selected cows are included. However, PTB surveys should also include pastoral local herds in the Sudan. It is interesting that Chi-Square showed no significant association between these descriptive animal data and serostatus (Table 2). |
Table 2
Chi square results for association between cattle age, sex, herd size and body condition and prevalence of MAP antibodies in Khartoum State
Result | Age | Body condition | Herd size | Sex |
> 3 | < 3 | Total | Emaciat-ed | Good | Total | L | M | S | Total | Female | Male | Total |
-ve | Count | 107 | 42 | 149 | 24 | 117 | 141 | 42 | 78 | 38 | 158 | 126 | 25 | 152 |
% within Result | 71.8 | 28.2 | 100.0 | 17.0 | 83.0 | 100.0 | 26.6 | 49.4 | 24.1 | 100.0 | 83.6 | 16.4 | 100.0 |
% within category | 91.5 | 97.7 | 93.1 | 100.0 | 91.4 | 92.8 | 95.5 | 92.9 | 92.7 | 93.5 | 92.6 | 96.2 | 93.3 |
% of Total | 66.9 | 26.3 | 93.1 | 15.8 | 77.0 | 92.8 | 24.9 | 46.2 | 22.5 | 93.5 | 77.9 | 15.3 | 93.3 |
+ve | Count | 10 | 1 | 11 | 0 | 11 | 11 | 2 | 6 | 3 | 11 | 10 | 1 | 11 |
% within Result | 90.9 | 9.1 | 100.0 | 0.0 | 100.0 | 100.0 | 18.2 | 54.5 | 27.3 | 100.0 | 90.9 | 9.1 | 100.0 |
% within category | 8.5 | 2.3 | 6.9 | 0.0 | 8.6 | 7.2 | 4.5 | 7.1 | 7.3 | 6.5 | 7.4 | 3.8 | 6.7 |
% of Total | 6.3 | 0.6 | 6.9 | 0.0 | 7.2 | 7.2 | 1.2 | 3.6 | 1.8 | 6.5 | 6.1 | 0.6 | 6.7 |
Total | Count | 117 | 43 | 160 | 24 | 128 | 152 | 44 | 84 | 41 | 169 | 136 | 26 | 163 |
% within Result | 73.1 | 26.9 | 100.0 | 15.8 | 84.2 | 100.0 | 26.0 | 49.7 | 24.3 | 100.0 | 83.4 | 16.0 | 100.0 |
% within category | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
% of Total | 73.1 | 26.9 | 100.0 | 15.8 | 84.2 | 100.0 | 26.0 | 49.7 | 24.3 | 100.0 | 83.4 | 16.0 | 100.0 |
*The chi square results showed that the association between cattle age and the prevalence of MAP antibodies was not significant (chi-value = 1.9, p > 0.05); similarly the association between the cattle body condition and the prevalence of such antibodies was insignificant (chi-value = 2.2, p > 0.05). Niether sex nor the herd size was significantly associated with the prevalence of MAP antibodies ( chi-value = 0.5, p > 0.05) and ( chi-value = 0.38, p > 0.05), respectively. |
The only reliable report from the Sudan on seroprevalence of bovine PTB to compare the current results with is that of Mohammed and others [24] who reported 66.7% and 10.2% prevalence at the herd and individual animal levels, respectively in Khartoum State. These rates are higher than that reported here, but our study seems to be more representative by involving greater number of herds distributed over a wider area of Khartoum State (Fig. 1). Moreover, they involved clinical cases, which when excluded, the apparently healthy animals would reveal a comparable animal-level prevalence (6.9%). Contrary to the current results they reported the lowest seropositivity in Omdurman.
It is obvious that PTB in Sudan is poorly documented. Similarly, reports from African countries on MAP infections in animals are rather scanty [26]. However, the prevalence rates, herd or individual animal levels, reported from Egypt [19], Uganda [20], and Tanzania [21] are reasonably comparable with the present results. Global prevalence of PTB is high and the disease is well documented in many developed countries, where it causes tremendous economic losses. The prevalence rates of PTB obtained in this study seem to be low compared to that mentioned globally [13, 15–18].
Generally, variation between results obtained by various authors may be influenced by stage of infection, animal age, shedding level of the organism, lactation, antibody concentration and varying sensitivity among different ELISAs [5, 8, 25, 27]. These should be considered when comparing results on PTB prevalence.
It has been stated that ELISA is more precise in determining herd level prevalence [8], however, combination of ELISA with culture or molecular assays for screening of MAP infection would be more reliable in investigating both animal and herd level prevalence.