Abstract
Haemonchus contortus is the most pathogenic gastrointestinal helminth of small ruminants. Natural or experimental repeated infections and several native antigens confer a partially protective immune response but vaccination with subunit antigens has been elusive. Promising results have been obtained with a recombinant form of a somatic antigen (rHc23). In this paper we present the results obtained in vaccination trials in lambs using two dosages of rHc23 and standard adjuvants. Six-months old Manchego females lambs were vaccinated with rHc23 (50 or 200 μg/dose) adjuvanted with 1mL aluminum hydroxide on days -42, -28 and -14 or with 200 μg/dose rHc23 and 5 mg Quil A on days -49, -28 and -7. Control lambs were kept receiving only the adjuvants the same days or no treatment. Moreover one group did not receive any treatment or infection. On day 0 vaccinated lambs, untreated animals and those receiving the adjuvant were infected per os with a monospecific single infection of 4000 L3 of H. contortus. Infection was kept for 58 days and follow-up included the determination of serum specific antibody response (ELISA, WB), hematological parameters (eosinophil counts, hematocrit) and fecal egg counts (epg). Absence of hematocrit alterations, reduction of helminth’s eggs output and abomasal parasite burden at the end of the experiment were the efficacy criteria of vaccination with the recombinant. Immunization with both adjuvants and antigen dosages elicited strong antibody responses particularly with Quil A. Vaccinated groups showed significant reduction of fecal egg excretion and abomasal helminth burdens. Highest protection of lambs against challenge was achieved with aluminum hydroxide and 200 μg/dose rHc23 with a reduction of over 70% of the abomasal burden and over 80% of fecal egg output. Results suggest that rHc23 could be a valuable recombinant candidate for vaccination against haemonchosis. No clear relationship was found between antibody levels and protection this pointing towards involvement of both humoral and cellular components in the protective response elicited by rHc23.
Highlights
IntroductionThe disease caused by Haemonchus contortus, is probably the most relevant and represents ca.15% of all gastrointestinal diseases of small ruminants (http://www.fao.org)
Infections of ruminants by gastrointestinal nematodes (GIN) are present worldwide
Higher optical density (OD) average values were found in the groups only receiving the adjuvants (G3 and Group 5 (G5)) there were not differences with primarily infected (G6) or uninfected control lambs (G7)
Summary
The disease caused by Haemonchus contortus, is probably the most relevant and represents ca.15% of all gastrointestinal diseases of small ruminants (http://www.fao.org) Infection by this gastric nematode, present in all areas with significant sheep and goats numbers, is more common in warm areas and this helminth has been considered the “nemesis” of small ruminant production systems in tropical and subtropical regions of the world [1]. Using a similar approach to that used to develop Bm86 vaccination against ticks [10], a native antigen of H. contortus has been marketed (Barbervax1) and is widely used in Australia This approach valuable has several limitations including the required number of boosters (5–6) [1, 11], the limited protection elicited in some cases [12] and the ethical concerns on the use of infected animals to obtain the “native” antigen for immunization. In the present study we present the results obtained in vaccination trials against lamb haemonchosis with rHc23 with different antigen doses and adjuvants
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