Genetic Control of Resistance to Trypanosoma brucei brucei Infection in Mice

Trypanosoma brucei are extracellular protozoa transmitted to mammalian host by the tsetse fly. They developed several mechanisms that subvert host's immune defenses. Therefore analysis of genes affecting host's resistance to infection can reveal critical aspects of host-parasite interactions. Trypanosoma brucei brucei infects many animal species including livestock, with particularly severe effects in horses and dogs. Mouse strains differ greatly in susceptibility to T. b. brucei. However, genes controlling susceptibility to this parasite have not been mapped. We analyzed the genetic control of survival after T. b. brucei infection using CcS/Dem recombinant congenic (RC) strains, each of which contains a different random set of 12.5% genes of their donor parental strain STS/A on the BALB/c genetic background. The RC strain CcS-11 is even more susceptible to parasites than BALB/c or STS/A. In F2 hybrids between BALB/c and CcS-11 we detected and mapped four loci, Tbbr1-4 (Trypanosoma brucei brucei response 1–4), that control survival after T. b. brucei infection. Tbbr1 (chromosome 3) and Tbbr2 (chromosome 12) have independent effects, Tbbr3 (chromosome 7) and Tbbr4 (chromosome 19) were detected by their mutual inter-genic interaction. Tbbr2 was precision mapped to a segment of 2.15 Mb that contains 26 genes

Co-administration of Albendazole and Levamisole to control multiple anthelmintic resistant nematodes in a sheep farm in Kabete Kenya

Albendazole (ABZ) and levamisole (LEV) were co-administered to evaluate their ability to control natural helminth infections in a sheep farm where resistance to the individual anthelmintic had previously been reported. Thirty two sheep of mixed ages and sex were randomly allocated to four equal groups. Group 1 and 2 were treated with ABZ and LEV respectively. ABZ and LEV were co-administered to group 3 while group 4 was the untreated control. Rectal faecal samples were collected from all the animals on the day of treatment (0 DPT) and fourteen days post-treatment (14 DPT) and the eggs per gram of faeces (EPG) determined. On both sampling occasions, pooled feacal samples from the respective groups were separately cultured for strongyle larval stage three (L3) identifications. Anthelmintic efficacies were evaluated based on faecal egg count reduction percentage (FECR%). Resistance to both drugs was still evident at FECR% of 71% and 75% for LEV and ABZ respectively. Co-administration of the two drugs resulted in a higher efficacy at 95.4% FECR %. L3 recovered from faecal culture 14DPT indicated that Haemonchus spp. survived treatments with ABZ and LEV given separately and when co-administered. Trichostrongylus spp. survived the LEV treatment but was highly susceptible to ABZ given alone or when co-administered with LEV, while Oesophagostomum species survived ABZ given separately. Combining these two drugs may therefore offer a temporary solution in helminth control on the farm as other control measures are sort.Key words: Efficacy, resistance, albendazole, levamisole, co-administratio

Seasonal patterns of gastrointestinal nematode infections in sheep in a semi-arid Kajiado District of Kenya

The seasonal patterns of trichostrongylid nematode infections in Dorper yearlings in a semi-arid area of Kajiado District, Kenya were investigated by analysis faecal egg output, herbage infectivity and post-mortem worm recovery. Rectal faecal samples from 60 animals as well as herbage samples from their grazing fields were collected at three weeks intervals between May 1999 and December 2001. Fecal egg counts and herbage larval counts closely followed the rainfall distribution pattern. Major peaks in egg output occurred between December and August as a result of increased pasture infectivity and minor peaks between September and November following maturation of hypobiotic larvae of Haemonchus. Self-cure occurred in August/ September and November/ December. From September 2000 to July 2001, post-mortem worm counts conducted on 24 yearlings permanently on pastures during the dry and wet seasons showed mixed infections where Trichostrongylus, Haemonchus and Oesophagostomum occurred in 91.7%, Cooperia in 83.3%, Trichuris and Strongyloides in 4.1% of the animals. Adult and immature worms co-existed in proportions that varied with seasons, where Haemonchus survived the dry season mainly as hypobiotic larvae and Trichostrongylus species as an adult worm population. The mean wet season worm counts in both seasons were considered moderate, usually associated with sub-clinical helminthosis and decreased productivity. There is need, therefore, to control such infections in sheep within the study area in order to achieve higher productivity. Bulletin of Animal Health and Production in Africa Vol. 54(1) 2006: 1-

Multiple Anthelmintic Resistance On A Sheep Farm In Kenya And Its Implication For Helminth Control

The occurrence of anthelmintic resistance in gastrointestinal nematodes in sheep on a farm in Kabete, Kenya was investigated between October 2005 and March 2006 when an outbreak of acute and fatal helminthosis occurred despite the use of ivermectin in worm control. The efficacies of locally available anthelmintics, namely, ivermectin, levamisole, levamisole rafoxanide combination and albendazole were evaluated based on faecal egg count reduction percentages (FECR%), clinical manifestation of helminthosis and post-mortem worm count (WC). All drugs tested showed low efficacies with FECR% of 44.2%, 77.0%, 66.9% and 42.3% for ivermectin, levamisole, levamisole rafoxanide combination and albendazole respectively. During the test period, 18 clinical cases were observed out of which 10 died. The mean WC in the dead animals declined gradually from 8905 in the pre-treatment period to 1545, 1529, 618, and 111 following ivermectin, levamisole, levamisole rafoxanide combination and albendazole treatments respectively. Haemonchus contortus and Trichuris ovis were resistant to all drugs tested. Trichostrongylus species were resistant to ivermectin and levamisole, but susceptible to albendazole. This necessitated treatment of the entire flock with albendazole and movement to new pastures and pens. No clinical case of helminthosis or mortality was recorded one month after the movement. This study indicated presence of multiple anthelmintic resistance on the farm as reported elsewhere in the country. Based on these findings, it is necessary to educate farmers on adapting integrated approach to helminth control with appropriate use of anthelmintics.Les cas de résistance anthelminthique chez les nématodes gastro-intestinaux dans une ferme ovine à Kabete au Kenya ont fait l\'objet d\'enquête entre octobre 2005 et mars 2006 lorsqu\'un foyer d\'helminthiase aigue et mortelle est apparu malgré l\'usage de l\'ivermectine pour le contrôle des vers. L\'efficacité des anthelminthiques disponibles sur place, à savoir : l\'ivermectine, le levamisole, l\'association levamisole/rafoxanide et l\'albendazole a été évaluée en tenant compte du taux de réduction du nombre d\'oeufs dans les fèces (% FECR), du signe clinique de l\'helminthiase et du nombre de vers à la nécropsie (NV). Tous les médicaments testés avaient une efficacité réduite avec des %FECR de 44,2% ; 77% ; 66,9% et 42,3% pour l\'ivermectine, le levamisole, l\'association levamisole/rafoxanide et l\'albendazole respectivement. Pendant la période de test, 18 cas cliniques ont été observés, parmi lesquels il y a eu dix morts. Le NV moyen chez les animaux morts baissait peu à peu, allant de 8905 avant le traitement à 1545, 1529, 618 et 111 après les traitements à l\'ivermectine, au levamisole, à l\'association levamisole/rafoxanide et à l\'albendazole respectivement. Haemonchus contortus et Trichuris ovis étaient résistants à tous les médicaments testés. Les espèces Trichostrongylus étaient résistantes à l\'ivermectine et au levamisole, mais sensibles à l\'albendazole, ce qui a rendu nécessaire le traitement de tout le troupeau à l\'albendazole et le déplacement vers de nouveaux pâturages et parcs à moutons. Aucun cas clinique d\'helminthiase ou de mortalité n\'a été enregistré un mois après le déplacement. Cette étude a montré la présence de résistance anthelminthique multiple sur la ferme comme signalé ailleurs dans le pays. A la lumière de ces conclusions, il est nécessaire de donner de l\'instruction aux éleveurs pour ce qui est de l\'adaptation de la méthode d\'approche intégrée au contrôle de l\'helminthe avec l\'usage judicieux des anthelminthiques.Bulletin of Animal Health and Production in Africa Vol. 55 (4) 2007: pp. 226-23