Field Application of a Subunit Vaccine against an Enteric Protozoan Disease

Background: Coccidiosis is a major global veterinary health problem in intensively reared chickens. It is caused by apicomplexan parasites of the genus Eimeria. Principal Findings: A subunit vaccine composed of purified antigens from the gametocytes of Eimeria maxima was used to stimulate the production and transfer of maternal antibodies between breeding hens and their hatchlings. The vaccine was injected into hens twice before they began laying eggs. Immunization had no adverse affects on egg laying or health of the hens and resulted in high antibody levels throughout the life of the hens. Progeny of immunized hens excreted significantly less oocysts of various species of Eimeria in their faeces than chicks from unvaccinated hens. Furthermore, the offspring of vaccinated hens developed stronger natural immunity to Eimeria, so that they were resistant to challenge infection even at 8 weeks of age, well after all maternal antibodies had left their circulation. Field trials were conducted in South Africa, Brazil and Thailand, involving at least 1 million progeny of vaccinated hens and at least 1 million positive control birds (raised on feed containing anticoccidial drugs or immunized with a live vaccine) in each country. Additionally, trials were carried out in Israel involving 60 million progeny of vaccinated hens and 112 million positive control birds. There were no significant differences in growth rate, feed conversion ratios or mortality in the offspring of vaccinated hens compared with the positive control chickens in any of these countries regardless of different management practices, different breeds of chickens or climate. Conclusions: These results demonstrate that a vaccine composed of antigens purified from the gametocytes of Eimeria can be used safely and effectively to prevent the deleterious effects of coccidiosis. It is the first subunit vaccine against any protozoan parasite to be successfully applied on a commercial scale. © 2008 Wallach et al

The effect of maternal immunization with purified gametocyte antigens of <i>Eimeria maxima</i> on the growth performance of progeny broiler chickens raised under commercial conditions on farms in Brazil, Thailand, Israel and South Africa.

<p>Commercial broiler breeder hens (Ross and Cobb breeds) were vaccinated twice with purified gametocyte antigens (PGA) at 15 and 20 weeks of age. Eggs were collected from groups of vaccinated and unvaccinated hens, incubated to hatching and broiler birds raised under normal commercial conditions for each country. Control flocks were either immunized with a commercial live vaccine or raised on feed containing anticoccidial chemoprophylactic drugs. There was no significant difference between the performance of control and vaccinated birds with respect to age at slaughter, mortality, Feed Conversion Rate (FCR), final body weight or European (EU) Performance Index (one-way ANOVA).</p>*<p>These farms were from large integrations, and the results are from several chicken houses run over a period of 2–3 years.</p>**<p>The results from Israel are the summary from several different farms run over a period of 5 years.</p

The effect of vaccination with purified gametocyte antigens of <i>Eimeria maxima</i> on mortality and egg production by breeding hens.

<p>Breeding hens were injected intramuscularly with 50 µg of purified gametocyte antigens emulsified in 0.5 ml of water-in-oil adjuvant at 15 and 20 weeks of age. Mortality rates and egg production of the flocks of hens were monitored until the end of their productive lives (around 60–65 weeks of age). Neither mortality or egg production were affected by vaccination (one-way ANOVA).</p

Effect of maternal immunization with purified gametocyte antigens of <i>Eimeria maxima</i> on weight loss due to infection with multiple species of <i>Eimeria</i> in progeny chickens.

<p>Commercial broiler breeder hens (14,532 vaccinated with purified gametocyte antigens and 7,256 control) were vaccinated twice with purified gametocyte antigens, (at 15 and 20 weeks of age). Eggs were collected from groups of vaccinated and unvaccinated 43 week old hens and incubated to hatching. Three different groups of 100 broiler chickens were raised: (A) chicks from unvaccinated hens, the chicks being raised in wire cages, with care being taken that they were not exposed to coccidian oocysts (i.e. non-exposed control group); (B) chicks from unvaccinated hens, the chicks being raised under normal commercial conditions on floor litter that was seeded with <i>Eimeria</i> oocysts; and (C) chicks from hens vaccinated twice with purified gametocyte antigens (CoxAbic), the chicks being raised under normal commercial conditions on floor litter that was seeded with <i>Eimeria</i> oocysts. When the birds were 10 days old, eight out of one hundred birds were orally infected with a cocktail containing 50 oocysts from each of four species of <i>Eimeria – E. maxima</i>, <i>E. tenella</i>, <i>E. acervulina</i> and <i>E. mitis</i>. Weekly checking of the litter for oocysts confirmed that the infections were successful in all groups of birds, with peaks of between 300,000 and 459,000 oocysts being found in every gram of floor litter. At 34 days of age, the birds were weighed. Results are means±S.E. Group B chicken weight was significantly lower than both Groups A and C (p<0.0001, one-way ANOVA, Student's t-test), which were not significantly different from each other.</p

The effect of maternal immunization with purified gametocyte antigens of <i>Eimeria maxima</i> on the development of resistance to <i>Eimeria tenella</i> in offspring chickens.

<p>Commercial broiler breeder hens (14,532 vaccinated with purified gametocyte antigens and 7,256 control) were vaccinated twice with purified gametocyte antigens, (at 15 and 20 weeks of age). Eggs were collected from groups of vaccinated and unvaccinated 43-week old hens and incubated to hatching. At 4 days of age, four groups of 15 male chicks from vaccinated and unvaccinated hens were challenged with 50 oocysts of <i>E. tenella</i>. At 39 and 57 days of age four groups of 15 chicks from each of vaccinated and unvaccinated hens were challenged with 25,000 oocysts of <i>E. tenella</i>. Faeces were collected from days 4–14 after challenge infection and oocyst counts performed. Oocyst excretion is expressed in two ways: [i] by peak oocyst excretion, which is a measure of the highest number of oocysts per gram of faeces on a single day after challenge infection (generally day 7 post-challenge) for groups of 15 chickens; and [ii] overall oocyst excretion, which is a measure of the number of oocysts per gram faeces found in the total faecal collection for days 4 to 14 post-challenge for groups of 15 chickens. The differences for both the peak and total oocyst counts in the vaccinated and control groups at the three time points are all statistically significant at the p<0.05 level (one-way ANOVA, Student's t-test).</p

Effect of immunization with purified gametocyte antigens of <i>Eimeria maxima</i> on gametocyte antigen-specific antibody levels in flocks of breeding hens.

<p>Commercial broiler breeder hens were vaccinated twice with purified gametocyte antigens (PGA) at 15 and 20 weeks of age. Sera (10–15 samples per flock) were collected at each time point post vaccination from 10 flocks of chickens (six from Israel, two from South Africa, and one each from Argentina and Thailand). The ELISA results are expressed as an S/P ratio, which is calculated as follows: (Sample optical density value – Negative control optical density value)/(Positive control optical density value – Negative control optical density value). Results show the average S/P±Standard Error for the ten flocks at different times post-vaccination. The average S/P for four control flocks from some of the same farms that were tested during the testing period are also shown.</p