Prevalence of BTB in Cattle Herds in Nigeria

Tuberculin skin testing (TST) of cattle using the single intradermal comparative cervical test (SICCT) was first carried out in 1939 on 507 animals on a government farm in Vom, Northern Nigeria.

In total, a prevalence of 1.4% was recorded using post-mortem inspection for the confirmation of the presence of lesions caused by M. bovis (Alhaji 1976). Several studies, though mostly limited to government- owned farms (Alhaji 1976; Cadmus and Ayanwale 2014; Cadmus et al. 2010), have been conducted since then. To date, the largest number of herds and animals screened in a coordinated manner was carried out in 26 local government areas in four states in the former Northern Nigeria (Alhaji 1976). In total, 13,487 cattle from 346 herds (representing about 0.13% of the national cattle herd at the time, and including nomadic, semi-nomadic, resident, commercial, and government-owned herds) were subjected to the single caudal fold test (CFT) using bovine-purified protein derivative (PPD). In all, 2.8% positive and 3.2% suspect reactors were identified. The positive reactors per herd ranged from 0% (only two herds) to 25%. Of the six major breeds of cattle examined (i.e. Bunaji, Rahaji, Sokoto, Adamawa Gudales, Wadara, and Azwak), the Rahaji, which accounted for 14.7% of all cattle screened, was the most affected (31.2%). The investigation further revealed that BTB was widespread in all the breeds of cattle, in different husbandry systems, and in all states in the region. Overall, based on nation-wide tuberculin tests of cattle herds from 1929 to date, the average BTB prevalence varies from 1.8 to 24%.

Between 1980 and the late 1990s, several governmental and public activities were disrupted or downscaled, and infrastructure destroyed by military incursions. The livestock sector suffered a tremendous downturn following these events, and from then the attention given to livestock only focused on a few serious diseases of economic importance; surveillance for BTB was not carried out in pastoral herds in Nigeria until 1999.

Even today, tuberculin skin tests are not used for routine BTB surveillance in the whole of Nigeria. It is usually only used by researchers working

Table 17.1 Surveys of BTB using the tuberculin skin test in Nigerian cattle

Location/region	Sample size	Test	Prevalence	Year	References
North	56	STC	24%	1929	Manley (1929)
North	507	SICCT	1.38%	1939	Mettam (1939)
North	13,497	CFT	2.5%	1975/ 1976	Alhaji (1976)
Ibadan, South-west	171	SICCT	10.5%	2004	Cadmus et al. (2004)
Kaduna and Federal Capital Territory, Abuja, Northcentral	967	SICCT	14.6%	2007	Abubakar (2007)
North-west, North-central, and South-west	1360	SICCT	5.7% (45.5% herd prevalence)	2010	Cadmus et al. (2010)
Jigawa, North-west	885	SICCT	2%	2012	Ibrahim et al. (2012)
Taraba, North-east	17	SICCT	11.8%	2012	Ayele et al. (2004) and Danbirni et al. (2012)
North-east	20,000	SICCT	12.2%	2011 2014	Salisu I (unpublished data)
Akure, South-west	36	SICCT	1.1%	2014	Adefegha et al. (2014)

SICCT single intradermal comparative cervical test, CFT caudal fold test, STC short thermal technique

on BTB (either locally or in collaboration with foreign institutions), in segments of areas that are readily accessible (Table 17.1).

Between 2004 and 2005, 33 selected herds in Northern and Southern Nigeria subjected to tuberculin skin testing, had a BTB prevalence of 45.5%. At the animal level, the infection prevalence ranged from 2.9 to 16.6% in the two regions. Poor management and the absence of disease control were identified as key factors causing these pockets of infections (Cadmus et al. 2010). However, in a coordinated effort to rekindle surveillance of BTB in Nigeria, the Federal Government of Nigeria funded a regional study between 2011 and 2014 to determine the status of BTB in cattle herds in North-eastern Nigeria. Through this initiative, the about 20,000 cattle screened had a reactor prevalence of about 14% (I. Salisu, unpublished data). However, considering the unrestricted movement of animals, poor management, and unhygienic practices including poor sanitary measures, and huge under-funding and limited governmental support of the livestock sector, the data presented so far on BTB in Nigeria are limited, and what is known may just be the tip of the iceberg and a total underestimation of the actual current state of affairs.

Based on the results of the exploratory tuberculin tests carried out to date, there is sufficient evidence to suggest that BTB is endemic in pastoral herds in all the regions of Nigeria.

It is also clear that over the years, BTB has spread from neighboring countries and Northern Nigeria to the southern parts of the country due to unrestricted cattle movement within and across different states, and across international borders (Cadmus et al. 2006; Abubakar 2007; Muller et al. 2009). The situation becomes more alarming when the herd prevalence is considered, and the finding that at least one animal is positive in the majority of the herds screened, should be a red flag given the absence of BTB control in Nigeria. However, since very few herds/animals have been screened to date, the epidemiological information obtained so far is inadequate to provide an insight into the true scale of BTB in Nigerian cattle herds and to allow the compilation of an adequate strategy to control the disease (Cadmus and Ayanwale 2014).

If tuberculin screening of cattle in Nigeria is going to be of any value, the challenge posed by concurrent helminth infections must also be resolved. Adedipe et al. (2014) and Adedipe (2014) reported 41.6 and 2.8% for gastrointestinal helminth and helminth-BTB co-infection, respectively, in slaughtered cattle in Ibadan, southwestern Nigeria. It is known that helminth infections adversely complicate estimation of the true status of BTB in cattle herds (Claridge et al. 2012). Until the way helminth-BTB co-morbidity influences the tuberculin skin test is resolved, determining the true extent of BTB in Nigeria may not be possible.

17.4

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Source: Dibaba A.B., Kriek N.P.J., Thoen C.O. (eds.). Tuberculosis in Animals: An African Perspective. Springer,2019. — 453 p.. 2019

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