If control of Neospora caninum infection is technically feasible does it make economic sense?

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    l a,b

    Box 5

    ariecDepartment of Medical and Biomolecular Sciences, University of Technology Sydney,

    f industry, with only minor changes expected in the relationships of


    Veterinary Parasitology 142 (Keywords: Cattle; Neospora caninum; Abortions; Costs; Decision tree; Economics; Control

    1. Introduction

    Neospora caninum is a protozoan parasite, which

    has been shown to occur world-wide (Dubey, 1999) in

    many countries including Australasia (Reichel, 2000).

    The parasite causes disease in dogs (neonatal death,

    hindleg paralysis) while in cattle it causes abortions,

    which imposes significant economic loss on farmers.

    Up to 50% of abortions that occur on a farm might be

    due to N. caninum (Anderson et al., 1995; Boulton

    et al., 1995; Thornton, 1996). This is especially so on

    farms that experience abortion storms, which affect a

    large proportion of the pregnant herd (Thornton et al.,

    1994). Other N. caninum-infected herds may experi-

    ence sporadic abortions (Davison et al., 1999), thought

    to occur when cattle are chronically infected (pre-

    sumably via the congenital route) (Hall et al., 2005a).

    While the epidemiology of the disease is still poorly* Corresponding author.

    E-mail address: michael.reichel@gribbles.com.au (M.P. Reichel).

    0304-4017/$ see front matter # 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.vetpar.2006.06.027# 2006 Elsevier B.V. All rights reserved.approach is likely to be applicable to other countries and the bee

    decisions versus within-herd prevalence of N. caninum infectReceived 17 March 2006; received in revised form 15 June 2006; accepted 21 June 2006


    Recent work on Neospora caninum, a protozoan parasite that causes abortions in dairy cattle has focused on a number of

    different control options. Modelling has suggested the most effective options for control but the present paper argues that the most

    effective option might not necessarily be optimal from an economic point of view. Decision trees, using published quantitative data,

    were constructed to choose between four different control strategies. The costs of these interventions, such as test and cull,

    therapeutic treatment with a pharmaceutical, vaccination or doing nothing were compared, and modelled, in the first instance, on

    the New Zealand and Australian dairy situation. It is argued however, that the relative costs in other countries might be similar and

    that only the availability of a registered vaccine will change the decision tree outcomes, as does the within-herd prevalence of N.

    caninum infection. To do nothing emerged as the optimal economic choice for N. caninum infections/abortions up to a within-

    herd prevalence of 18%, when viewed over a 1-year horizon, or 21% when costs were calculated over a 5 years horizon. For a higher

    (21%) within-herd prevalence of N. caninum infection vaccination provided the best (i.e. most economic) strategy. Despite beingthe most efficacious solutions, test and cull or therapeutic treatment never provided a viable economic alternative to vaccination or

    doing nothing. Decision tree analysis thus provided clear outcomes in terms of economically optimal strategies. The sameP.O. Box 123, Broadway, New South Wales 2007, AustraliaIf control of Neospora can

    feasible does it ma

    Michael P. ReicheaGribbles Veterinary Pathology, P.O.

    bMacquarie Graduate School of Management, Macqum infection is technically

    economic sense?,*, John T. Ellis c

    36, Palmerston North, New Zealand

    University, Sydney, New South Wales 2109, Australia


    2006) 2334

  • the costs of various control options and, via a decision

    tree analysis (Fig. 1),1 to determine which option might

    be economically optimal. The general outcomes

    however appear to be easily transferable to the situation

    in other countries where N. caninum infection is also

    known to be a cause of abortions and an issue of

    economic concern.

    M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 233424

    Fig. 1. Decision tree analysis.

    structure upon a decision process otherwise not seen, and gives the

    process transparency that allows the decision process to be easily

    challenged and ultimately changed and improved upon. The nodes of

    the tree represent either a decision point or a chance/probability event;

    decision nodes are marked out as squares, chance nodes by circles. At

    the end of the branches one inputs the outcomes (costs or gains):

    terminal values or pay-offs of the decisions or probabilities. Rolling-

    back the outcomes (from right to left) to the beginning of the tree,

    one multiplies the outcomes by their probabilities (on branches

    emanating from chance nodes) and sums up the results for each

    branch emanating from the same node. The strategy that has the

    largest benefit (or least cost) is chosen at the decision point/node. For

    more information on decision trees, see: http://www.psychwww.com/

    mtsite/dectree.html or Smith and Slenning (2000).understood (it was only first described in 1984, Bjerkas

    et al., 1984), in recent years advances have been made

    in the diagnosis of the disease and serological tests have

    been developed for the accurate identification of

    infected animals (Pare et al., 1995a, 1995b). The

    sensitivity and specificity of those, in particular the

    ELISA tests, have been well described over the past few

    years (von Blumroder et al., 2004). With the use of

    those diagnostic tools, epidemiological studies have

    determined a very high efficiency of the (vertical)

    transmission of the parasite from dam to daughter (Pare

    et al., 1994) and have given rise, recently, to test-and-

    cull attempts of eradication of the infection from a herd

    (Hall et al., 2005a). Sero-prevalence data for New

    Zealand (Reichel, 1998) and Australia (Hall et al.,

    2005b) range from 6.75% to 22% of cattle, respectively.

    Other control options (Reichel and Ellis, 2002) that

    have been discussed and developed, are vaccination

    (Andrianarivo et al., 1999) and chemotherapy (Kritzner

    et al., 2002). Vaccination with a killed tachyzoite

    formulation, while reported to be highly efficacious in

    rodents (Liddell et al., 1999) has not had the same

    success rate in cattle (Romero et al., 2004) and is

    estimated to be only 50% efficacious in that species.

    This strategy of vaccination also appears to be

    reasonably expensive and labour-intensive, requiring

    two vaccinations per annum initially, and each year

    thereafter. Chemical treatment, while reported to be

    highly efficacious (>90%) (Kritzner et al., 2002) is alsoexpensive and can be expected to present residue

    problems in food producing animals such as cattle.

    Herds with persistent N. caninum infection will

    continue to incur costs of abortion (loss of the calf, loss

    of milk, veterinary costs), yet there are also reports of

    improved neonatal mortality in infected calves (Pare

    et al., 1996) and reports of the effects of N. caninum

    infection on milk production are mixed (Hall et al.,

    2005a; Hobson et al., 2002; Pfeiffer et al., 2002).

    While previous studies have either modelled (French

    et al., 1999) or practically focused on the technical

    feasibility and efficacy of N. caninum eradication from

    a herd (Hall et al., 2005a), the question also should be

    asked whether these control options make economic

    sense. The present paper developed a model (using

    decision tree analysis) for determining the relative cost/

    benefit relationship of various control options of N.

    caninum infection in a dairy herd based on currently

    available (and published) information from the relevant

    literature, modelled in the first instance on the

    Australasian dairy situation. The New Zealand situa-

    tion, in particular, where a vaccine for N. caninum is

    now available, affords a unique opportunity to model2. Assumptions for the construction of the

    decision tree

    2.1. Infection

    The probability of a dairy herd being infected with N.

    caninum was assumed to be 30% (Otranto et al., 2003).

    National surveys for New Zealand have suggested a

    national prevalence in individual dairy cattle of up to

    9% (Reichel, 1998). Other reports of within-herd

    prevalence (Schares et al., 1999) and recent survey

    work in Australia has suggested a state-prevalence for

    1 This refers to a particular technique in decision theory for analys-

    ing and evaluating problems that contain a degree of uncertainty or

    probability through visualisation of the alternatives in a hierarchical,

    tree-like structure. They are particularly useful where decisions are

    made at discreet points (in time) and in a sequential order. Their

    particular value not only lies in the outcomes, but in the clear layout of

    the decision-making process, which enforces a certain degree of

  • M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 2334 25NSW of 22% (Hall et al., 2005b). In herds experiencing

    abortion storms in Australasia, the within-herd pre-

    valence appears to be higher (but remarkably con-

    sistent) at around 30% (Atkinson et al., 2000; Thornton

    et al., 1994). Overseas, authors are also reporting

    higher and lower within-herd prevalences of N.

    caninum infection (Barling et al., 2001; Schares

    et al., 2003).

    2.2. Abortions

    Abortions due to N. caninum were assumed to occur

    in New Zealand and Australian dairy cattle at a

    probability of three times greater in N. caninum-

    infected than in the uninfected cattle population (Moen

    et al., 1998; Thurmond et al., 1997; Wouda et al.,

    1998), which has recently been reported to be

    experiencing about 6.9% foetal loss (McDougall

    et al., 2005). As some of these (6.9%) losses are

    caused by N. caninum, a background figure for other

    abortions of 5% was assumed for those farms where

    sporadic abortions were experienced. Therefore, a 15%

    sporadic abortion risk was assumed for N. caninum-

    infected cattle. Sporadic abortions were assumed to

    constitute the majority (P = 0.9) of N. caninum abor-

    tions, with abortion storms far less likely (P = 0.1)

    (Anderson et al., 2000).

    In abortion storms of epidemic proportions, 50% (i.e.

    10 times greater risk) ofN. caninum-infected cattle were

    assumed to abort (Atkinson et al., 2000; Cox et al.,

    1998; Lopez-Gatius et al., 2004; Schares et al., 1999;

    Wouda et al., 1999). Once a farm had experienced an

    abortion storm (in year 1), it was assumed that only

    sporadic N. caninum-induced abortions (with the three-

    fold increased risk) would occur in subsequent years

    (Innes et al., 2000).

    2.3. Costs/losses incurred due to N. caninum

    2.3.1. Cows

    In the event of an abortion occurring, the total cost of

    abortion was calculated as the cost of a replacement in-

    calf heifer (NZ$ 1400.00) minus the meat (cull)

    value of the aborting cow (NZ$ 500.00), giving a total

    cost/loss for an abortion event of NZ$ 900.00

    (Deverson, 2005).

    2.3.2. Veterinary costs

    The initial veterinary investigation of an abortion

    case (of either, the sporadic or of the epidemic storm-

    type) was assumed not to exceed NZ$ 400.00 (Hill,

    personal communication).2.3.3. Testing

    Serological testing of cows (as a precursor to further

    intervention in the case of the test-and-cull policy) was

    assumed to cost NZ$ 10.00 a sample, assuming a

    volume discount (based on the assumption of a whole

    herd test).

    2.3.4. Other cost assumptions

    Other serological testing, for instance to establish the

    within-herd prevalence of N. caninum infection per se,

    have been treated as a sunk cost (i.e. as a cost one

    would have incurred in any case, regardless of the

    outcomes and these are excluded from the calculations

    of alternatives). Similarly, the cost of abortions which

    are not caused by N. caninum, have been disregarded

    from all options (as they are assumed to have been

    incurred by all alternatives) and thus only the

    incremental, N. caninum-related costs have been

    included. Therefore, the total cost for the non-infected

    70% of herds is set at zero.

    Effects of N. caninum infection on milk production

    are mentioned in the literature, with varying, i.e.

    positive (Hall et al., 2005a; Pfeiffer et al., 2002), as well

    as negative (Hernandez et al., 2001; Thurmond and

    Hietala, 1997b) impacts recorded. These have also been

    excluded from the decision trees (even though some

    authors mention this factor as one of the most important

    cost drivers, Chi et al., 2002). Equally, the reported

    possible positive effects of N. caninum on neonatal

    mortality in calves have been excluded (Pare et al.,

    1996), as have increased costs of veterinary treatments

    in infected cows or effects on weight gain that have been

    reported in the literature (Barling et al., 2000).

    2.4. Treatment optionscosts

    2.4.1. No intervention (do nothing)

    The probability of abortion storms and sporadic

    abortions were assumed to be as discussed in Section

    2.2 on abortions (see above) with however only the

    likelihood of one abortion storm occurring in a herd

    over the observation period, being contemplated. N.

    caninum repeat abortions are generally regarded to be

    rare (Cox et al., 1998; Thurmond and Hietala, 1997a)

    (although others disagree, Obendorf et al., 1995;

    Thornton et al., 1991) and hence abortion storms were

    only assumed to occur once (in the first year) and

    sporadic abortions assumed in subsequent years.

    2.4.2. Test-and-cull

    Test-and-cull was assumed to be preceded (as

    discussed above) by an all-herd serological test,

  • assuming the national mean size of a dairy herd in New

    Zealand of 300 milking cows (Anon, 2005a), with an

    equal number of young (replacement) stock (150 heifer

    calves, 150 heifers).

    Culling was assumed to occur in one (the first) year

    (presenting a high present cost) calculated as the cost of

    the replacement (NZ$ 900.00) of any infected cows

    times their number.

    With the rapid replacement of infected cows in year

    1, no further abortion events were assumed until year 5,

    when the probability of infection within the herd

    (derived from post-natal infection at the rate of 0.01/

    year, Hall et al., 2005a; Pare et al., 1996) was assumed

    to have reached a level of 5%.

    2.4.3. Treatment

    While thus far only used in a research setting

    (Kritzner et al., 2002), treatment with BayCox1 (active

    communication), with two doses required in the first and

    subsequent years (Romero et al., 2004). Vaccination

    was assumed each year for both the adult cow herd and

    the, also at risk, replacement (in-calf) heifer cohort. The

    efficacy of the vaccine was assumed to be 50% (Romero

    et al., 2004), thus allowing abortion storms and

    sporadic abortions to continue to occur at half the

    assumed rate. However, as discussed above, N. caninum

    repeat abortions are generally regarded to be rare so

    abortion storms were only assumed to occur once (in the

    first year) and sporadic abortions assumed in subsequent


    2.4.5. Sensitivity analysis

    The resultant costs of each control option were

    calculated for individual scenarios by varying within-

    herd prevalences of N. caninum infection. Reported

    within-herd prevalences vary from less than 10% to in

    M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 233426

    and daingredient: Toltrazuril) was included as an alternative

    treatment in the decision tree. Treatment was costed

    over a 6-day period (at a cost of NZ$ 568.80 per average

    500 kg cow), with a projected additional loss of the

    average milk production per day (17 l at 30 cents a litre)

    for a fortnight.

    Assuming the high efficacy of 90% for the treatment

    reported in the literature (Kritzner et al., 2002), only

    10% of the remaining N. caninum-infected cattle were

    assumed to be at risk of either abortion storms or

    sporadic N. caninum-induced abortions.

    2.4.4. Vaccination

    Vaccination (Bovilis Neoguard1, Intervet, NZ) was

    assumed to cost NZ$ 5.00 per dose (Wylie, personal

    Fig. 2. Cost (NZ$) of four treatment options in an average New Zeal

    prevalence of Neospora caninum infection of 15%.excess of 90% (Frossling et al., 2005; Mainar Jaime et al.,

    1999; Pare et al., 1998; Thurmond et al., 1997; Wouda

    et al., 1999). They were calculated in Microsoft Excel and

    entered into the decision tree developed (Fig. 2). The

    resultant total costs were analysed for two scenarios; for a

    period of 1 year of observation, but also over 5 years, with

    the costs in years 25 discounted at a rate of r = 0.1, and

    the present values entered into the decision tree (Frino

    et al., 2004). The costs of the various treatment options

    were calculated on the basis of an average sized dairy

    herd in New Zealand with 300 milking cows (Anon,

    2005a) and 200 cows in Australia (Anon, 2005b).

    In order to address the limitations that come with

    point estimates only, lowest (labelled best) and

    highest (labelled worst) (in terms of their effect on

    iry herd (n = 300 cows) over a 1-year period at an assumed within-herd

  • M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 2334 27


























































































































































































































































































































































































    ioncosts) assumptions were also modelled in addition to the

    assumptions above (labelled average); in the case of

    sporadic abortion risks of 10% and 20% were modelled

    (in addition to the average 15%), for abortion storms

    25% (i.e. five times increased risk) and also 75% of

    cows aborting were modelled (average 50%), as well

    as a sporadic abortions to storms split of 8095%

    (sporadic) to 520% (storms).

    2.4.6. Decision tree

    Decision trees were built using software (TreeAge

    Pro Suite) available from TreeAge Software Inc. (http://


    3. Results obtained from decision tree analyses

    Decision tree analysis arrived at a number of optimal

    solutions, depending on the within-herd prevalence of

    N. caninum infection, the type of scenario (best,

    worst or average) and the length of the observa-

    tion period. Up to a within-herd prevalence of 18% (and

    considering the costs/benefits only over a 1-year period)

    the do nothing option was calculated to be the

    cheapest (Table 1a; Fig. 2). However, in the worst

    case scenario (highest cost of abortions), that threshold

    was reached earlier (at a within-herd prevalence of

    10.7%) while in the best scenario (lowest cost of

    abortions) the threshold was not reached until the

    within-herd prevalence went beyond 31%. For within-

    herd prevalences equal to and greater than 18% (range

    10.831.1%), the vaccination option was increasingly

    the best option for the farmer when costs were only

    considered over a 1-year period.

    If costs were viewed over a longer-term period, such

    as 5 years (and costs in future years discounted at a rate

    of 10% to give the present value of those costs in todays

    dollars, taking into account the best alternative rate of

    financial return on the money invested, say, in the share

    market), then the breakpoint for a switch between do

    nothing and vaccination was reached at prevalences

    equal to and greater than 21% (Table 1a; Fig. 3), but

    ranging from 32.7% (best) to 14.7% (worst),

    depending on scenario.

    The incremental benefits of vaccination (compared

    to the next best (costlier) alternative option), viewed

    over a 1-year period, increase from NZ$ 495.00 (at herd

    level) at a 20% level of N. caninum infection to NZ$

    7987.00 if the within-herd prevalence of N. caninum

    infection was assumed to be 50% (Table 2). This

    represents a return on investment (ROI) of up to 177.5%

    (Table 2) at existing prices for the vaccine option. In the

    worst case scenario, with assumptions leading to the

  • M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 233428

    and dahighest costs of abortion, at 15% prevalence, the ROI of

    vaccination is 39.5%, while in the best case scenario,

    there is a ROI of 29% for vaccination but only at 40%


    A calculation of costs, via decision trees, of the do

    nothing option at herd and industry level was

    performed for a 1- and 5-year period at varying

    within-herd prevalences. Costs of N. caninum abortions

    to the national dairy industry rise from a 5% average

    within-herd prevalence level of N. caninum infection at

    NZ$ 10.4 million per annum to NZ$ 91.4 million if the

    within-herd prevalence in infected herds was assumed

    to be 50%, to NZ$ 152.1 million if the costs of the

    worst case scenario were calculated (Table 3).

    Fig. 3. Cost (NZ$) of four treatment options in an average New Zeal

    prevalence of N. caninum infection of 20%.Similar calculations were made for Australia where

    average dairy herds are smaller at 200 cows (Anon,

    2005b), but other costs, such as replacement heifers are

    similar. The decision tree approach arrives here at an

    Table 2

    Cost benefit (NZ$) of vaccination and return on investment (ROI) (%, in pa

    infection in a herd over a 1- or 5-year period)


    prevalence (%)

    Optimal solution per scenario (1-year horizon) (ROI, %)

    Worst Average Best

    5 N/Aa N/Aa N/Aa

    10 N/Aa N/Aa N/Aa

    15 $ 1777.50 (39.5) N/Aa N/Aa

    20 $ 3870.00 (86.0) $ 495.00 (11.0) N/Aa

    30 $ 8055.00 (179.0) $ 2992.00 (66.0) N/Aa

    40 $ 12,240.00 (272.0) $ 5490.00 (122.0) $ 1305.00 (2

    50 $ 16,425.00 (365.0) $ 7987.00 (177.5) $ 2756.25 (6

    a Not applicable as do nothing option is the least costly.annual cost to the Australian dairy industry of AU$

    21.2 million (assuming 10,000 herds, Anon, 2005b)and AU$ 7060.00 for the N. caninum-infected herd with

    an assumed prevalence of N. caninum infection of 20%

    (Hall et al., 2005b).

    4. Ramifications of the decision tree approach

    Control options for N. caninum infections in dairy

    cattle have been discussed in recent years (Reichel and

    Ellis, 2002), and some authors have also recently

    embarked on control efforts, based on the test and cull

    strategy, with good success (Hall et al., 2005a). These

    efforts, and other reports in the literature, have provided

    iry herd (n = 300 cows) over a 5-year period at an assumed within-herdvaluable data on which to model (by decision tree

    analysis) the cost and benefits of various control

    methods. Others have previously modelled the costs of

    N. caninum abortions to herd and industry in New

    rentheses) over the do nothing option (i.e. the cost of N. caninum

    Optimal solution per scenario (5-year horizon)

    Worst Average Best

    N/Aa N/Aa N/Aa

    N/Aa N/Aa N/Aa

    $ 351.06 (1.9) N/Aa N/Aa

    $ 6722.88 (35.8) N/Aa N/Aa

    $ 19,466.52 (103.7) $ 7985.04 (42.6) N/Aa

    9.0) $ 32,210.15 (171.7) $ 16,901.52 (90.1) $ 4157.88 (22.2)

    1.3) $ 44,953.79 (239.6) $ 25,817.99 (137.6) $ 9888.45 (52.7)

  • M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 2334 29

    iry ind








    25,42Zealand (Pfeiffer et al., 1997), but those efforts failed to

    identify the costbenefits to the farm entity or the dairy

    industry as a whole of treatment/eradication efforts as

    they present themselves now. The New Zealand

    situation, where a vaccine for N. caninum is now

    available, affords a unique opportunity to model the

    costs of various control options and, via a decision tree

    analysis, to determine which option might be the

    optimal one. In another recent paper (Larson et al.,

    2004), testing for N. caninum infection and excluding

    female offspring from breeding was considered to be

    the best economic decision in beef herds in the US.

    These authors however looked at the effect of endemic

    abortions only (not abortions) and did not include the

    option of vaccination, nor to the do nothing in their

    three options for comparison.

    The current analysis demonstrates that N. caninum

    infection is costly to the individual average-sized herd,

    as well as to the dairy industry in New Zealand as a

    whole, with on-farm costs on infected farms rising (with

    increasing levels of prevalence of infection) from NZ$

    2897.50 (at 5% prevalence) to NZ$ 25,375.00 in herds

    when 50% of cattle are infected. With national

    prevalence surveys putting the prevalence at between

    Table 3

    Overall average cost (NZ$) of N. caninum infection at the herd and da

    over a 1- and 5-year horizon


    prevalence (%)


    One-year period Five-year perio

    5 $ 869.25 ($ 555.381375.50) $ 3175.33 ($ 2

    10 $ 1618.50 ($ 990.752631.00 $ 5850.27 ($ 5

    15 $ 2367.75 ($ 1426.133886.50) $ 8525.21 ($ 7

    20 $ 3117.00 ($ 1861.505142.00) $ 11,200.16 ($

    30 $ 4615.50 ($ 2732.257653.00) $ 16,550.04 ($

    40 $ 6114.00 ($ 3603.0010,164.00) $ 21,899.93 ($

    50 $ 7612.50 ($ 4473.7512,675.000 $ 27,249.82 ($10% and 20% (Hall et al., 2005b; Reichel, 1998) in

    Australasia, the likely cost of N. caninum infection to

    the New Zealand dairy industry can be estimated by the

    present model at NZ$ 28.4 million (at 15% prevalence)

    (ranging from $ 17.1 to 46.6 million), a figure

    remarkably similar to the one (NZ$ 24 million)

    modelled by others earlier (Pfeiffer et al., 1998).

    Pfeiffer et al. (1998), however modelled their national

    costs on a within-herd prevalence of 35% and a risk of

    N. caninum abortions of only 5%, with no differentia-

    tion between the risk of abortion storms versus the risk

    of sporadic abortions. More recent data from Austra-

    lasia that were not available to those earlier workers

    have flown into the present model, which assumes agreater risk of abortion for infected cows (310 times

    higher) and models both, sporadic and epidemic

    (abortion storm-like) abortions. It is thus not

    surprising that the present model arrives at the same

    national cost with a considerably lower within-herd

    prevalence of N. caninum infection.

    Previously the annual cost to the Australian dairy

    industry had been estimated to be around AU$

    85 million (Ellis, 1997). At that time state or national

    data for N. caninum infections were not available, thus

    the estimate of the current paper, while considerably

    lower than those previously published, appear to give a

    more accurate assessment of the total cost of N.

    caninum infection to the Australian dairy industry.

    The present model suggests that up to a within-herd

    prevalence of 18% (in the average scenario) the do

    nothing option is the optimal economic decision to the

    farmer. If, however, the within-herd prevalence of N.

    caninum-infection exceeds 18%, then vaccination has

    clear economic benefits (at the present cost of NZ$ 5.00

    a dose) with returns on investments (ROI) rapidly

    increasing, proportional with increasing prevalence,

    from 11.0% (20% prevalence of infection) to 177.5%

    (50%) viewed over the short-term. Viewed over the

    ustry level in New Zealand (range best to worst in parentheses)

    Industry (million $)

    One-year period Five-year period

    83357.58) $ 10.4 ($ 6.716.5) $ 38.1 ($ 35.940.3)

    76214.77) $ 19.4 ($ 11.931.6) $ 70.2 ($ 65.874.6)

    69071.96) $ 28.4 ($ 17.146.6) $ 102.3 ($ 95.7108.9)

    1.1611,929.16) $ 37.4 ($ 22.361.7) $ 134.4 ($ 125.7143.1)

    6.5417,643.54) $ 55.4 ($ 32.891.8) $ 198.6 ($ 185.5211.7)

    1.9323,357.93) $ 73.4 ($ 43.2122.0) $ 262.8 ($ 245.3280.3)

    7.3229,072.32) $ 91.4 ($ 53.7152.1) $ 327.0 ($ 305.1348.9)longer term (5 years) the returns on investment from

    vaccination at prevalences of infection exceeding 20%

    range from 42.6% (at 30% prevalence) to 137.6% (at


    The best and worst possible case scenarios clearly

    show (Table 1a) how these decision thresholds move

    with changes to some of the probabilities, with the

    worst case (resulting in the highest cost of abortions)

    making vaccination the economically optimal decision

    from a within-herd prevalence of N. caninum infection

    of greater than 10.7%, while with assumptions in the

    best case scenario, this threshold was not reached

    until a 31% prevalence of N. caninum infection in the


  • Viewed over 1 year only, the major cost and decision

    driver is the cost of an abortion storm. It contributes

    10% only of the risk/cost in the decision tree, but if the

    gap between the cost of losing a large number of calves

    and having to replace cows versus paying insurance by

    means of vaccination is large enough, it tilts the balance

    in favour of vaccination. That happens at 18% within-

    herd prevalence of infection.

    Over the 5 years time frame, we assume in our model

    only one abortion storm event and the literature also

    suggests that abortion storms are not going to occur

    they are highly efficacious control options) (Hall et al.,

    2005a; Kritzner et al., 2002). This is due to their much

    higher up-front costs (incurred in the first year) in

    eliminating the infection (testing and culling, treatment

    costs). Our modelling however suggests, that the gap to

    the more economical control options continues to

    persist, even if costs were spread out over a number of


    It is important to note that, more efficacious

    vaccines, such as the live vaccines which have recently

    been described (Guy et al., 2005) could significantly

    M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 233430

    Table 4

    Decision thresholds of within-herd prevalences (%), where a highly (100%) efficacious vaccine for N. caninum, applied annually or once in a cows

    lifetime becomes the most economical choice

    Evaluation time frame Scenarios if applied annually Scenarios if applied once

    Worst Average Best Worst Average Best

    One year 4.8 8.2 14.1 4.8 8.2 14.1

    Five years 6.7 9.5 14.9 2.0 2.8 4.5every year. Sporadic abortions only are expected/

    assumed for the other 4 years. Thus the cost drivers are,

    both, the increasing gap between the cost of losing

    calves (and having to replace cows) in an abortion storm

    and the cost of the vaccine (as over 1 year) but, in

    addition, the cumulative cost of sporadic abortions,

    which continue at half the rate despite vaccination.

    It is interesting to observe that test-and-cull, or

    treatment strategies never get close to becoming an

    economically viable option, despite the fact that they

    may appear (on technical grounds) to be preferable (asFig. 4. Cost (NZ$) of various options for N. canreduce or completely remove the risk of any cattle in the

    herd aborting (as had to be assumed, despite vaccina-

    tion, for 50% of the cattle receiving the Intervet

    vaccine). This reduces N. caninum control to the cost of

    vaccination alone, providing a viable alternative to

    doing nothing even at very low within-herd

    prevalences of infection with N. caninum. However,

    whether or not this vaccine needs to be applied annually

    or just once in the life time of a cow influences the

    decision on when vaccination becomes the economic

    optimal one. Over a 1-year time frame, the decisioninum control viewed over a 1-year horizon.

  • M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 2334 31

    r N.thresholds range from 14.1% (best) to 4.8%

    (worst), with the average scenario threshold at

    8.2% (Table 4; Fig. 4).

    However, even with best or worst case

    assumptions, the threshold prevalences between doing

    nothing or vaccination with such a highly efficacious

    vaccine (applied only once in a cows life time) would

    reduce to a range of only 2.5% points (from 2%

    (worst) to 4.5% (best) prevalence, with 2.9%

    being the average), when viewed over a 5 years

    Fig. 5. Costs (NZ$) of various control options fohorizon (Table 4; Fig. 5). This would reduce the

    uncertainty for the farmer considerably, meaning that at

    any prevalence over 5%, vaccination (in any scenario)

    would be the most economical decision to make.

    Bovilis Neoguard1 (Intervet) is currently not

    registered in Australia. In all combinations of

    Fig. 6. Costs (AU$) of control options in an average Australian dairy herd (n

    of N. caninum infection of 20%.within-herd prevalence versus period of observation

    for Australia, therefore, the do nothing option

    appears as the economically optimal one, since the

    other two treatment strategies (treatment or test and

    cull) have very high up-front costs (Fig. 6). This

    situation could be expected to be similar in most other

    countries around the globe without a registered

    vaccine. This would seem to provide an ideal

    opportunity for a vaccine manufacturer (such as

    Intervet in the first instance), to enter the Australian

    caninum control viewed over a 5 years horizon.(or any other) market, with what is essentially a well-

    priced alternative to living with the disease, providing

    good returns on investment, especially in herds with

    higher (than 15%) within-herd probabilities of infec-

    tion with N. caninum. Similarly, calculations and

    decision trees as outlined here could be constructed for

    = 200 cows) over a 1-year period at an assumed within-herd prevalence

  • M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 233432each and every country where N. caninum is known to

    cause abortions, and it would not appear unreasonable

    to assume that the decision would not significantly

    change as the replacement value of dairy cattle appears

    to be remarkably similar in a number of major dairy

    producing countries at around the level (ranging from

    US$ 700.00 to 1425.00, Grohn et al., 2003; Gunn et al.,

    2005; Ott and Johnson, 2003; Santarossa et al., 2005;

    Stott et al., 2005) as used in the present assumptions.

    The threshold value (of infection, or vaccine price)

    where vaccination would become the economically

    preferred option might vary slightly (in the US where the

    Neoguard vaccine sells at US$ 3.50 a dose, it might vary

    downwards), the general trend, however, would remain

    the same: at very low within-herd prevalence of N.

    caninum to do nothing would be most economical,

    while at a certain (somewhat higher) prevalence the

    option of vaccination should become the preferred course

    of action. As the threshold value where the decision

    changes may well vary between countries, it seems

    prudent to construct a local decision tree before

    embarking on control (options) in other countries.

    The decision tree approach, which has been used and

    suggested in veterinary circumstances, such as for

    diagnostic testing (Smith and Slenning, 2000) or disease

    control decision analysis (Tomassen et al., 2002),

    demonstrates in the present example that control

    options that are technically sound and achievable do

    not necessarily present the most economic solution to a

    dairy farmer. When faced with N. caninum infection in a

    herd, a dairy farmer presently would need to choose

    control options that are currently less efficacious (such

    as vaccination) or do nothing since they represent the

    soundest economic decision to make. However, the

    future availability of more efficacious vaccines for the

    prevention of N. caninum abortions/infections would

    suggest vaccination will become the most economical

    control option to a farmer, where the within-herd

    prevalence of N. caninum infection exceeds 4.5%. By

    choosing the opportunity costs incurred in the event of

    abortions (the replacement present value of an in-calf

    heifer) the model presented here was simple without

    compromising the value of the outputs and is quickly

    applied to the situation in other countries or industries

    where N. caninum infection prevails.


    Dr. Fraser Hill, of Gribbles Veterinary Pathology,

    Palmerston North, New Zealand and Dr. David Morrison,

    of the National Veterinary Institute, Uppsala, Sweden are

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    M.P. Reichel, J.T. Ellis / Veterinary Parasitology 142 (2006) 233434

    If control of Neospora caninum infection is technically feasible does it make economic sense?IntroductionAssumptions for the construction of the decision treeInfectionAbortionsCosts/losses incurred due to N. caninumCowsVeterinary costsTestingOther cost assumptions

    Treatment options-costsNo intervention (do nothing)Test-and-cullTreatmentVaccinationSensitivity analysisDecision tree

    Results obtained from decision tree analysesRamifications of the decision tree approachAcknowledgementsReferences