The consequences of vaccination with the Johne's disease vaccine, Gudair, on diagnosis of bovine tuberculosis.

The single intradermal comparative cervical tuberculin skin-test (SICCT) remains the primary surveillance tool to diagnose bovine tuberculosis (BTB) in the UK. Therefore, understanding the potential confounding influences on this test is important. This study investigated the effects of vaccination against Johne's disease (JD) on the immunodiagnosis of BTB using a Mycobacterium bovis BCG vaccination model as a surrogate of M bovis infection. Calves were vaccinated with either BCG (an attenuated live vaccine) or the JD vaccine, Gudair (a heat-inactivated suspension of Mycobacterium avium subspecies paratuberculosis), or a combination of both, and SICCT responses were measured approximately six and 12 weeks postvaccination. Animals vaccinated with Gudair only were negative to the SICCT test, thus supporting the specificity of the SICCT test following Gudair vaccination. However, while animals vaccinated with BCG-only demonstrated a bovine tuberculin-biased response as expected, covaccination with Gudair resulted in a bias towards avian tuberculin in the SICCT test. Therefore, our model demonstrates the potential of the Gudair vaccine to reduce the sensitivity of the SICCT. In addition, while we also demonstrate that Gudair vaccination can compromise the specificity of serological tests to detect JD, the specificity of defined M bovis antigens in serological or interferon gamma-based blood assays was not compromised by the vaccine.

Lack of correlation between BCG-induced tuberculin skin test sensitisation and protective immunity in cattle.

Vaccination of cattle with Mycobacterium bovis Bacille Calmette-Guérin (BCG) can provide significant protection against bovine tuberculosis (TB). However, BCG vaccination sensitises animals to respond to the tuberculin skin-test. This provides a potential operational impediment to the use of BCG as a cattle vaccine since the tuberculin skin-test is the primary surveillance tool used by many countries with 'test and slaughter' control strategies. Currently, it is also unclear what BCG-induced skin-test conversion means in respects to BCG's protective immunity. In the current study we first investigated the duration of tuberculin skin-test sensitisation in calves neonatally vaccinated with BCG. BCG vaccination induced strong skin-test responses in calves during their first 6 months. However, a rapid decay in skin-test sensitivity was observed after this time. Between 6 and 9 months this represented a reduction from 80% to 8% of calves providing a positive response in the single intradermal comparative cervical tuberculin test at standard interpretation. We next investigated the relationship between BCG induced skin-test sensitivity and retention of protective immunity. Calves were neonatally vaccinated with BCG and subsequently divided into 2 groups based on retention or loss of tuberculin skin-test responses after 6 months. In contrast to their skin-test responsiveness, these vaccinates maintained their tuberculin specific IFN-γ blood responses. Moreover, irrespective of their pre-challenge skin-test responses, following M. bovis challenge both groups of BCG vaccinated calves demonstrated comparable levels of protection, as evidenced by reduced TB-associated pathology. Therefore, we have demonstrated that following neonatal BCG vaccination of cattle, tuberculin skin-test responder frequencies waned rapidly after 6 months but importantly, loss of skin-test sensitivity did not correlate with loss of protective immunity. These findings could have implications for the practical application of BCG based cattle vaccines.

Isoniazid treatment of Mycobacterium bovis in cattle as a model for human tuberculosis.

Cattle infected with Mycobacterium bovis spoligotype 9 were treated with Isoniazid (INH) from three to 14 weeks post infection, rested for fourweeks to allow INH depletion and then challenged with M. bovis spoligotype 35. Post mortem examination (PME) 35 weeks after the initial infection showed partial protection against infectious challenge following INH-attenuated infection compared with the spoligotype 35 challenge controls. Antigen-specific IFN-gamma responses decreased over time with INH therapy, following a similar pattern to that observed in the treatment of M. tuberculosis infection in humans. Following cessation of therapy, specific IFN-gamma responses increased more strongly in those calves that were visibly lesioned at PME. IFN-gamma responses were also used to identify two antigens, TB10.4 and Acr2, that induced anamnestic responses in INH-treated, re-challenged calves, suggesting a role for both antigens in protective immunity. Specific IL-10 responses were observed in all calves following treatment with INH suggesting a role for IL-10 in the resolution of infection.

Trypanosome infections and tick infestations: susceptibility in N'Dama, Gobra zebu and Gobra x N'Dama crossbred cattle exposed to natural challenge and maintained under high and low surveillance of trypanosome infections.

Susceptibility to trypanosome infections and tick infestations was assessed in 51 N'Dama, 48 Gobra zebu and 37 Gobra x N'Dama crossbred (F1) cattle exposed to field-tick infestations and natural high tsetse challenge over more than one year. From these cattle, 12 animals of each breed were randomly selected and examined parasitologically for trypanosome infections and packed cell volume (PCV) twice a week (high surveillance, group HS). In the remaining 100 cattle trypanosome infection and PCV were monitored monthly (low surveillance, group LS). Mortality rates were recorded in both groups. Tick infestation was quantified fortnightly from all animals in group HS and from four to seven randomly selected animals of each breed in group LS. In both HS and LS groups, trypanocidal drug treatment was administered to trypanosome positive animals with PCV equal to or less than 20% or when they showed clinical evidence (dullness, weight loss) of trypanosomosis. In both groups, N'Dama cattle exhibited a superior capacity to control trypanosome infections and limit tick burdens. Particularly, in group HS N'Dama cattle showed lower trypanosome infection rate, higher mean PCV value, lower requirement for trypanocide treatments and lower tick load than crossbred and Gobra cattle in the corresponding group (P < 0.05 or greater). This was also true in N'Damas in comparison with crossbreds in group LS. Unfortunately, the high mortality occurring in Gobra cattle in group LS did not allow within group comparative analysis between N'Dama, Gobra and crossbred cattle overall the study period. No death occurred in N'Dama cattle maintained under high surveillance of trypanosome infection, while approximately 8% of crossbreds and 50% of Gobras died of trypanosomosis. In group LS, all Gobra and more than 70% of crossbred cattle died. In this group, mortality in N'Dama was limited to less than 16%. In both groups, differences in mortality were significantly higher (P < 0.01) in Gobras than in N'Damas. Within breed, animals of the three breeds maintained under high surveillance of trypanosomal infection showed higher mean PCV values, lower tick burdens and required proportionally less trypanocide treatments than corresponding cattle in group LS. The infection rate in N'Dama under high surveillance was lower in comparison with N'Dama cattle in group LS. There was no significant difference in mortality between groups within the N'Dama breed. Conversely, mortality rates were lower in crossbred and Gobra in group HS than in respective cattle in group LS. It was concluded that cattle of the three breeds suffered from trypanosomosis and that trypanosome infections affected tick susceptibility. However, N'Dama showed a superior ability to limit both the pathological effects of trypanosomosis and the level of tick infestations. Therefore, considering the cost of labour and consumable equipment required for a high surveillance, use of multi-disease resistant N'Dama cattle is recommended for the low-input traditional African farming systems in areas where trypanosomosis, ticks and tick-borne diseases are constraints to livestock production. Additional comparative investigations are needed to assess the impact of high surveillance scheme of trypanosome infection in different production systems in trypanotolerant and trypanosusceptible cattle exposed to different gradients of tsetse challenge.

Susceptibility to different tick genera in Gambian N'Dama and Gobra zebu cattle exposed to naturally occurring tick infestations.

Tick collection on one side of the body and whole tail was performed weekly over one year on 11 Gambian N'Dama (Bos taurus) and 11 Gobra zebu (Bos indicus) cattle to assess breed susceptibility to naturally occurring ticks. Enzyme-linked immunosorbant assay was also performed to assess the serological prevalence of Anaplasma marginale antigen and Babesia bigemina antibody. Packed red cell volume was measured and liveweight gain was recorded. Significantly higher numbers of Amblyomma variegatum (P < 0.002) and Hyalomma spp. (P < 0.001) were found on Gobra zebu than on N'Dama cattle. The serological prevalence of A. marginale antigen was significantly (P < 0.001) lower in N'Dama breed, whilst no difference in the serological prevalence of B. bigemina antibody was found between N'Dama and Gobra cattle. Packed red cell volume was negatively affected by A. marginale infection in both breeds, but to a lesser extent in N'Dama cattle. Liveweight gain was significantly (P < 0.003) higher in N'Dama in comparison with Gobra cattle during the period of abundance of A. variegatum and Hyalomma spp. adults. The significantly lower burdens of A. variegatum and Hyalomma spp. ticks in Gambian N'Dama in comparison with Gobra zebu cattle confirms previous findings. It also shows a more deleterious effect of ticks and tick-borne diseases on animal production and health in Gobra zebu than in N'Dama cattle. The presence of a tick resistant trait in N'Dama cattle is suggested.

A comparison of the susceptibility of Djallonké sheep and West African Dwarf goats to experimental infection with two different strains of Trypanosoma congolense.

Two cloned strains of Trypanosoma congolense, of West and East African origin, were used to infect by intradermal inoculation two groups of young adult female Djallonké sheep and West African Dwarf goats. For a 3 month period post-infection, packed red cell volume (PCV), parasitaemia, body weight and clinical parameters were followed to evaluate their trypanotolerant nature and to control the pathogenicity of the two strains of T. congolense. Although the West African strain of T. congolense was more pathogenic than the East African strain, it seemed that the Djallonké sheep and the West African Dwarf goats, despite high levels of parasitaemia and a concomitant drop in PCV, showed a high degree of trypanotolerance, as reflected by zero mortality and an increase in body weight during 12 weeks of observation.

Comparative studies on N'Dama and zebu cattle following repeated infections with Trypanosoma congolense.

Twenty N'Dama and eight zebu cattle were inoculated intradermally with bloodstream forms of a cloned strain of Trypanosoma congolense originating from East Africa. All inoculated cattle became parasitaemic. Zebus showed consistently higher levels of parasitaemia and lower packed red cell volume (PCV) percentages than did N'Damas. Three of the eight zebus required treatment when high numbers of trypanosomes were present in the blood and PCV values dropped below 15 per cent. None of the N'Dama cattle needed treatment. Statistical analysis was performed on the data to assess the variability of parasitaemia and PCV levels before and during infection of the N'Dama cattle. The variation in PCV values was large between individuals during the early stages of the disease and diminished as infection continued. After trypanocidal drug treatment and a recovery period of 14 months, the same animals were inoculated intradermally with T congolense bloodstream forms isolated and cloned in The Gambia. Differences in susceptibility to the ensuing disease were apparent when comparing N'Dama and zebu cattle. Five zebu cattle needed trypanocidal drug treatment, while none of the N'Damas needed drug intervention. Ranking the 20 infected N'Damas according to average PCV levels revealed that the animals responded similarly to both infections.

Prevalence of anaplasmosis and babesiosis in N'Dama cattle of the Gambia.

Sera from 184 N'Dama cattle randomly selected and averaging 2-7 years of age were tested for the presence of specific antibodies to Anaplasma marginale, Babesia bovis and B. bigemina, using one or more serological tests including complement fixation, rapid card agglutination and indirect fluorescent antibody (IFA). Tests for A. marginale and B. bovis were essentially negative. Utilising the IFA test 65% of the sera tested were positive for B. bigemina. Three randomly selected two-year-old N'Dama bulls were splenectomised. All three showed an acute recurrence of a B. bigemina parasitaemia. Two died following typical signs of acute babesiosis and a third recovered following diminazene therapy. No evidence of either B. bovis or A. marginale recrudescence was observed in the single surviving bull. Babesia bigemina appears endemic in the N'Dama cattle of The Gambia but no confirmed serological or clinical evidence of B. bovis or A. marginale was observed.

Susceptibility to African trypanosomiasis of N'Dama and Zebu cattle in an area of Glossina morsitans submorsitans challenge.

The use of trypanotolerant livestock is considered to be an important strategy for the control of African animal trypanosomiasis. In order to define the extent of the differences in susceptibility and productivity, 10 Zebu cows (a breed considered trypanosusceptible) and 10 N'Dama cows (a breed recognised for trypanotolerance) were exposed to a natural field challenge from Glossina morsitans submorsitans Newstead. The animals were two-and-a-half to three years old and had not been previously exposed to trypanosomiasis. All Zebu died of trypanosomiasis within eight months of first exposure. In contrast, only three N'Dama died of trypanosomiasis; they had all been suckling calves before they succumbed 11 to 14 months after initial exposure. The prevalence, level and duration of parasitaemia were significantly less in the N'Dama, which, unlike the Zebu, did not become febrile during parasitaemia. The differences in parasitaemia were largely attributable to Trypanosoma vivax. The N'Dama also developed much less severe anaemia than the Zebu. The mean and standard deviation of the packed red cell volume of the N'Dama was not significantly different between eight months after exposure when all Zebu were dead, and 21 months when the experiment was terminated. The relative productivity of the N'Dama was impressive. In addition to reduced mortality, the N'Dama experienced no abortions and produced five calves, three of which were alive at the end of the experiment, at which time three of the surviving N'Dama were pregnant. In the Zebu, in marked contrast, abortions occurred both in early and late pregnancy and no live calves were produced. The study confirmed that N'Dama cattle are innately less susceptible to trypanosomiasis than Zebu cattle and can survive and be productive in endemic areas of trypanosomiasis where Zebu perish.