Process Development of Sj-p80: A Low-Cost Transmission-Blocking Veterinary Vaccine for Asiatic Schistosomiasis

Asiatic schistosomiasis caused by Schistosoma japonicum is a neglected tropical disease resulting in significant morbidity to both humans and animals - particularly bovines - in endemic areas. Infection with this parasite leads to less healthy herds, causing problems in communities which rely on bovines for farming, milk and meat production. Additionally, excretion of parasite eggs in feces perpetuates the life cycle and can lead to human infection. We endeavored to develop a minimally purified, inexpensive, and effective vaccine based on the 80 kDa large subunit of the calcium activated neutral protease (calpain) from S. japonicum (Sj-p80). Here we describe the production of veterinary vaccine-grade Sj-p80 at four levels of purity and demonstrate in a pilot study that minimally purified antigen provides protection against infection in mice when paired with a low-cost veterinary adjuvant, Montanide™ ISA61 VG. Preliminary data demonstrate that the vaccine is immunogenic with robust antibody titers following immunization, and vaccination resulted in a reduction of parasite eggs being deposited in the liver (23.4-51.4%) and intestines (1.9-55.1%) depending on antigen purity as well as reducing the ability of these eggs to hatch into miracidia by up to 31.6%. We therefore present Sj-p80 as a candidate vaccine antigen for Asiatic schistosomiasis which is now primed for continued development and testing in bovines in endemic areas. A successful bovine vaccine could play a major role in reducing pathogen transmission to humans by interrupting the parasitic life cycle and improving quality of life for people living in endemic countries.

The potential economic value of a Trypanosoma cruzi (Chagas disease) vaccine in Latin America

Background

Chagas disease, caused by the parasite Trypanosoma cruzi (T. cruzi), is the leading etiology of non-ischemic heart disease worldwide, with Latin America bearing the majority of the burden. This substantial burden and the limitations of current interventions have motivated efforts to develop a vaccine against T. cruzi.

Methodology/Principal Findings

We constructed a decision analytic Markov computer simulation model to assess the potential economic value of a T. cruzi vaccine in Latin America from the societal perspective. Each simulation run calculated the incremental cost-effectiveness ratio (ICER), or the cost per disability-adjusted life year (DALY) avoided, of vaccination. Sensitivity analyses evaluated the impact of varying key model parameters such as vaccine cost (range: $0.50–$200), vaccine efficacy (range: 25%–75%), the cost of acute-phase drug treatment (range: $10–$150 to account for variations in acute-phase treatment regimens), and risk of infection (range: 1%–20%). Additional analyses determined the incremental cost of vaccinating an individual and the cost per averted congestive heart failure case. Vaccination was considered highly cost-effective when the ICER was ≤1 times the GDP/capita, still cost-effective when the ICER was between 1 and 3 times the GDP/capita, and not cost-effective when the ICER was >3 times the GDP/capita. Our results showed vaccination to be very cost-effective and often economically dominant (i.e., saving costs as well providing health benefits) for a wide range of scenarios, e.g., even when risk of infection was as low as 1% and vaccine efficacy was as low as 25%. Vaccinating an individual could likely provide net cost savings that rise substantially as risk of infection or vaccine efficacy increase.

Conclusions/Significance

Results indicate that a T. cruzi vaccine could provide substantial economic benefit, depending on the cost of the vaccine, and support continued efforts to develop a human vaccine.

The substantial burden of Chagas disease, especially in Latin America, and the limitations of currently available treatment and control strategies have motivated the development of a Trypanosoma cruzi (T. cruzi) vaccine. Evaluating a vaccine's potential economic value early in its development can answer important questions while the vaccine's key characteristics (e.g., vaccine efficacy targets, price points, and target population) can still be altered. This can assist vaccine scientists, manufacturers, policy makers, and other decision makers in the development and implementation of the vaccine. We developed a computational economic model to determine the cost-effectiveness of introducing a T. cruzi vaccine in Latin America. Our results showed vaccination to be very cost-effective, in many cases providing both cost savings and health benefits, even at low infection risk and vaccine efficacy. Moreover, our study suggests that a vaccine may actually “pay for itself”, as even a relatively higher priced vaccine will generate net cost savings for a purchaser (e.g., a country's ministry of health). These findings support continued investments in and efforts toward the development of a human T. cruzi vaccine.

Prizes and parasites: incentive models for addressing Chagas disease

Recent advances in immunology have provided a foundation of knowledge to understand many of the intricacies involved in manipulating the human response to fight parasitic infections, and a great deal has been learned from malaria vaccine efforts regarding strategies for developing parasite vaccines. There has been some encouraging progress in the development of a Chagas vaccine in animal models. A prize fund for Chagas could be instrumental in ensuring that these efforts are translated into products that benefit patients.

The efficacy and economic benefits of Supercox®, a live anticoccidial vaccine in a commercial trial in broiler chickens in China

The efficacy and economic benefits of Supercox, a live anticoccidial vaccine were examined and compared with an anticoccidial drug in a trial in broiler chickens under modern commercial conditions in China. In total, 40,660 chickens were used in the present study, half of which were vaccinated with the Supercox vaccine comprising a precocious line of Eimeria tenella and non-attenuated lines of Eimeria maxima and Eimeria acervulina, and the other half were medicated with Diclazuril delivered as feed additive at the dosage of 1mg/kg of feed. The vaccine was administered orally to 7-day-old chickens. No clinical diseases were diagnosed in any of the vaccinated birds. However, clinical coccidiosis occurred in a large proportion of medicated control birds and these chickens had to be treated with anticoccidial drugs (Diclazuril and Toltrazuril). Comparison of production performance between vaccinated birds and medicated control birds revealed that the vaccine Supercox performed better than anticoccidial drugs in terms of mortalities, costs and overall economic benefits (profits). These findings demonstrated that the use of the Supercox vaccine could control clinical coccidiosis in broilers and achieve production performance superior to that using anticoccidial drugs, particularly where drug resistance might result in failure to control clinical diseases.

Infection of calves with Theileria annulata in Tunisia: Economic analysis and evaluation of the potential benefit of vaccination

A field study aiming to estimate the costs of tropical theileriosis was carried out in an endemic region of the North of Tunisia. Three farms were monitored for two successive summer seasons. A total number of 56 calves and 12 sentinel cows were monitored. Calves were ranked into four groups: non infected animals, diseased animals with clinical tropical theileriosis, sub-clinical Theileria annulata infected animals with anaemia and sub-clinical T. annulata infected animals without anaemia. The total costs due to disease and infection were estimated to be 15,115.058 TD (Euro 9388.20). A high proportion of these costs (50.81%) is accounted for by asymptomatic infection. Sub-clinical infections with anaemia showed the highest losses in live weight, while disease cases (prevalence 42.86%) are responsible for 23.64% of the losses with death as the most important element. A cost-benefit analysis of vaccination using a Tunisian attenuated cell line vaccine was also undertaken. Considering that the vaccine would cost 5 TD (Euro 3.10), the cost-benefit ratio of vaccination is 23.7. Sensitivity analysis of the vaccination costs shows that the indifference decision point is around 118 TD (Euro 73.29).

Epidemiological aspects and economic impact of bovine theileriosis (East Coast fever) and its control: a preliminary assessment with special reference to Kibaha district, Tanzania

A cross-sectional study based on clinical examination, inspection of herd health records and a questionnaire was designed to determine the epidemiology, economics and potential impact of immunisation against theileriosis in Tanzania. The results showed annual theileriosis costs to be US$ 205.40 per head, whereas the introduction of immunisation reduced this by 40-68% depending on the post immunisation dipping strategy adopted. Morbidity risk due to theileriosis was 0.048 in immunised and 0.235 in non-immunised cattle, and the difference was significant (chi(2)=66.7; P=0.000). The questionnaire results indicated that immunised cattle had a significantly (chi(2)=6; P=0.015) higher risk of anaplasmosis compared with non-immunised cattle, whereas the risk of bovine babesiosis did not differ significantly (chi(2)=0.06; P=0.807) between the two groups. Mortality risk due to anaplasmosis was 0.046 in immunised and 0.018 in non-immunised cattle and this difference was statistically significant (chi(2)=4.48; P=0.043). The theileriosis mortality risk was 0.203 in the non-immunised cattle, while the risk was 0.009 in the immunised cattle and these differences were also significant (chi(2)=103; P=0.000). It was concluded that farmers who have immunised their cattle may cautiously cut down acaricide application by 50% for extensively grazed herds and by 75% for zero grazed animals depending on the level of tick challenge at the herd level.

Economics of theileriosis control in Zambia

For an economic analysis of theileriosis control, we adopted the total economic cost (TEC) method, which calculates the sum of output losses from tick damage, theileriosis mortality and morbidity, and expenditures for treatment or prevention of the disease. At farm level, the TEC can be minimized by a specific combination of vector control and/or immunization and an acceptable level of losses. Expenditures for vector control include acaricides, construction of dipping or spraying facilities and their maintenance, and variable costs such as those for water and labour. Economics of vector control depend on the herd size and the method of application of the acaricide. Morbidity, mortality and tick damage losses are effectively reduced by correct and intensive vector control programmes. Expenditures for vector control are estimated at US$ 8. 43, 13.62 and 21.09 per animal per year for plunge dipping, hand spraying and pour-on, respectively. Immunization costs comprise production of parasite stabilates, storage and application, delivery and treatment. At US$ 9.5 per animal, immunization limits losses caused by Theileria parva, but ticks still may reduce the productivity of the animals. Expenditures for treatment after natural infection involve drugs, transport, veterinary fees and farm labour costs. Treatment has a moderate success rate, hence both morbidity and mortality remain important factors. Equally, it does not affect the vector, which may continue to reduce overall productivity of cattle. Expenditures for treatment range between US$ 9.04 and US$ 27.31 per animal. To compare different TECs in relation to different control strategies, assumptions have to be made on disease occurrence, case fatality, value and productivity of the cattle, reductions in productivity due to morbidity and number of animals under a specific control regime. Calculations based on data from Southern Province, Zambia show that large-scale immunization reduces the TEC by 90% compared to no intervention. Treatment, which is the second-best option, reduces the TEC by 60%. Appendix 1 Summary of factors influencing total economic cost

The efficacy and economic benefits of Paracox, a live attenuated anticoccidial vaccine, in commercial trials with standard broiler chickens in the United Kingdom

The first large-scale broiler trials under modern commercial conditions of Paracox, a live attenuated anticoccidial vaccine administered in the drinking-water, are reported from the United Kingdom. The vaccine, comprising all seven of the species of Eimeria that parasitise the domesticated fowl, was compared with anticoccidial drug shuttles (halofuginone then salinomycin, or nicarbazin then monensin) in nine trials comprising over 936000 chickens, all of which also received the digestive enhancer virginiamycin. No clinical diseases were diagnosed in vaccinated birds in any of the trials. Necrotic enteritis occurred in the medicated controls (anticoccidial drug shuttles) of 2/9 trials and coccidiosis occurred concurrently with one of these outbreaks. Using additional criteria that particularly reflected economic benefits, the vaccine performed overall at least as well as the drug shuttles. The crucial results for vaccinated and medicated birds were: feeding costs (pence per kg liveweight of birds that were processed), 33.9 pence (vaccinated) and 33.7 pence (medicated) (P=0.549); feed conversion ratios, 2.01 (vaccinated) and 1.96 (medicated) (P=0.025); coefficient of variation in mean bird weight before processing, 9.3% (vaccinated) and 9.0% (medicated) (P=0.300); birds found dead, 3.0% (vaccinated) and 3.8% (medicated) (P<0.001); culled birds 4.0% (vaccinated) and 3.8% (medicated) (P=0.483); birds rejected during processing, 1.1% (vaccinated) and 1.2% (medicated) (P=0.271). In addition, the mean total water consumptions per chick were 7.82 L (vaccinated) and 7.76 L (medicated) (P=0.611), whilst the mean percentages of dry matter in the litter were 76.2% (vaccinated) and 75.2% (medicated) (P=0.195). Accumulation of oocysts in the litter of chicks vaccinated at 5 days of age peaked at 21 and 35 days, compared with medicated controls which showed a single higher peak at 35 days. Hence, the use of Paracox vaccine may control clinical coccidiosis in broilers and also achieve performances at least equal to anticoccidial drugs, particularly where drug resistance might result in failure to control disease.

Financial analysis of East Coast fever control strategies in traditionally managed Sanga cattle in Central Province of Zambia

Five different East Coast fever (ECF)-control strategies (involving ECF immunisation by the infection-and-treatment method) were tested in groups of traditionally managed Sanga cattle in the Central Province of Zambia over a period of 2.5 years. Two groups were under intensive tick control (weekly spraying with acaricide)--one group immunised and the other non-immunised. Two groups were under no tick control--one group immunised and the other non-immunised. The fifth group was under seasonal tick control (18 sprays/year) and was immunised against ECF. The input and output data were used to construct discounted cash flows for each group. The seasonally sprayed and immunised group gave the highest net present value, and the non-immunised group with no tick control, the lowest. A break-even analysis showed that the immunisation costs could rise to US$25.9 per animal before profitability was affected. For herds under intensive tick control, immunisation was of no financial benefit. The results demonstrate the value of immunisation, and indicate the importance of its combination with seasonal tick-control measures.

Research on the schizont cell culture vaccine against Theileria annulata infection in Xinjiang, China

Theileria annulata infection (TAI) is one of the most serious diseases of cattle in Xinjiang Autonomous Region of Uigur Minority Nationality. It has been recorded in 14 prefectures, except the Tulufan Prefecture, but the enzootic areas are mainly distributed around the Zhunger Basin and Talim Basin. According to the records collected in the ten years before vaccination with the schizont cell culture vaccine was carried out, the average incidence rate of TAI in enzootic areas was 7.22% and the mortality rate was 24%. The milk production of cattle suffering from TAI was sharply decreased, and there were usually abortions in pregnant cows. The incidence rate and mortality rate were greater in high grade cattle, so TAI was a constraint to improving cattle breeds. To control this disease effectively in Xinjiang, researchers at the Xinjiang Academy of Animal Science began to study the schizont cell culture vaccine in 1972. In 1977 an immortalised cell line was achieved from a primary cell culture starting with white blood cells from cattle suffering from acute TAI caused by an artificial tick bite. The cell culture medium mainly consisted of calf serum, lactalbumin-hydrolysate, Eagles' medium DMEM and three antibiotics. As a vaccine, the above cells were mixed with preserving medium containing gelatin. This paper describes the experiments on the immunological properties of the vaccine carried out in subsequent years. Up to 1996, vaccine doses for 1,186,150 cattle have been produced and sold. This vaccine has had a critical effect on the control of TAI in Xinjiang. Owing to the sharp decrease in the incidence rate and mortality rate of TAI after cattle were vaccinated, the annual economic benefit of the vaccine is at least 1,620,000 yuan.

Assessing the economic impact of immunisation against East Coast fever: a case study in coast province, Kenya

The cost of immunising cattle against East Coast fever by the infection and treatment method has been calculated for a pilot scheme in Kaloleni Division of the Coast Province of Kenya by using a spreadsheet model. The cost was calculated to be KSh 544 (US$25) per animal (in 1990 values). If a farmer were to bear all this cost, immunisation would be financially profitable in grade cattle, but the benefits of immunisation would not be sufficient to justify the immunisation of zebu cattle. For these animals, the cost of immunisation would have to be in the range of KSh 230 to KSh 415 per animal, or the farm-gate price of milk would have to increase by at least 80 per cent from KSh 7.50 to 13.50/litre, or the government would have to subsidise the cost either partially or fully. The first two possibilities are realistic, because the costs of routine immunisation are likely to be lower than for the pilot scheme, and because the increasing demand for milk is likely to push up prices in the liberalised markets. If both the grade and zebu cattle in Kaloleni Division were targets for immunisation, it is estimated that there would be 14,500 head for immunisation annually, costing an estimated KSh 8 million. The spreadsheet model used to assess the economics of immunisation in the Kaloleni Division could be applied to determine the government or private veterinary service charges for immunisation that would be financially profitable to farmers in a defined cattle production system in any division, district or country. The model could also be used to estimate the annual total number of cattle for immunisation in a target cattle production system and thus help with the financial planning for the exercise.