Diagnosis of helminth infections in cattle: were we wrong in the past

1
Diagnosis of helminth infections in cattle were
we wrong in the past?

• Jozef Vercruysse, Johannes Charlier, Pierre Dorny
  Edwin Claerebout
• Ghent University, Faculty of Veterinary Medicine,
  Merelbeke, Belgium

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Helminth infections of cattle

• Helminth infections of cattle are ubiquitous and
  continue to pose the greatest infectious disease
  problem in grazing livestock
• Helminth infections of cattle are mainly caused
  by
• Gastrointestinal (GI) nematodes e.g. Ostertagia
  ostertagi, Cooperia oncophora, Haemonchus sp
• Lungworms (Dictyocaulus viviparus)
• Liver flukes (Fasciola hepatica)

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Success of control

• Since the 60 and until 90 commercial release
  of a vast range of wonder anthelmintics (high
  efficacy, safe, ease of use)
• The current control strategies, based on
  anthelmintic use have resulted in a dramatic
  decrease in cases of clinical parasitism
• Nowadays cattle producers treat their whole herd
  at regular intervals rather to maximise
  production than to avoid disease.

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This is history ?
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Important for the future

• A responsible use of anthelmintics because
• Non-chemotherapeutic approaches not yet a
  practical option
• Likelihood of new anthelmintics becoming
  commercially available seems remote
• Anthelmintic resistance need to delay the
  emergence

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The problems

• To optimise anthelmintic treatments the key
  problem remains to identify those
  herds/individual animals requiring treatment
• AND
• Conventional diagnostic techniques for worm
  infections are laborious, and often not
  informative in providing a decision on whether to
  treat an animal/herd or not.

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Diagnosis in the past

• In the past emphasis was mainly put on the
  estimation of parasite numbers
• (egg worm counts)

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Were we wrong?

• For too long parasitologists did not consider
  that morbidity does not only depend on the
  intensity of infection but also on many other
  factors

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What can we do?

• To identify animals that require treatment we
  need to develop indicators that detect both
  parasite levels and sequelae of this parasite
  infection on production traits.

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Objectives presentation

• The factors contributing to morbidity in helminth
  infections of cattle
• The limitations of the existing conventional
  diagnostic techniques
• Innovative parameters for identification of
  animals/herds requiring treatment

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Factors contributing to morbidity

• It is apparent that the severity of pathology
  resulting from a certain worm burden does vary
  between hosts.
• Many factors are likely to be responsible for
  much of these variations
• Immunity status
• Intercurrent diseases
• Age, sex
• Nutrition
• Host Genetics
• .

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Correlation between wormburden, immunity and
non-specific factors
Wormburden
0



Death
Clinical disease
Subclinical disease
Nonspecific factors
Immunity status of host
No evident disease
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The problem (1) Assessment of economic losses

• Incomplete information on the exact interplay
  between levels of infection in relation to
  production
• Geographical variation in importance of
  production indices
• Breed variation in resilience and resistance to
  infection
• The complex interplay with levels of nutrition,
  immunity, age and concurrent infection with other
  parasites and infectious agents.

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The problem (2) Assessment of economic losses

• Using a mixed effects logistic regression model
  for analyzing association between risk factors
  and disease it was shown that about 50 of the
  total variance on the logit scale for the
  probability of disease was attributable to
  unmeasured or unmeasurable group-level factors.

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The problem (3) Assessment of economic losses

• Our lack of understanding of the complex play of
  the factors involved in production losses
  undermines our ability to represent these losses
  as a simple function of some index of parasitism
• Even if various indices of parasitism may be
  correlated with production losses it may be
  expected that these correlations exist only at
  particular times in the infection cycle.

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Recoverable cost

• It is not because a parasite has been identified
  to cause a decreased productivity, that these
  losses may all be recoverable through control of
  the infection
• e.g. fasciolosis was associated with a drop in
  milk yield of 14, however, only 8 was
  recoverable through treatment.

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Objectives presentation

• The factors contributing to morbidity in helminth
  infections of cattle
• The limitations of the existing conventional
  diagnostic techniques
• Innovative parameters for identification of
  animals/herds requiring treatment

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Conventional diagnostic techniques

• Detection of eggs/larvae in faeces still the
  standard for diagnosing endoparasites
• Determination of specific antibodies commercial
  tests available for lungworms and Fasciola

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Detection of eggs/larvae in faeces

• High specificity, moderate sensitivity
• Reasonable indication of infection
  levels/efficacy
• Difficulties of sampling
• Techniques labour-intensive ? numbers to be
  examined are low
• Absence of a threshold value between
• high FEC, resulting in high infection levels
  with reduced weight gains
• low FEC that will result in low infection
  levels without production losses

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Determination of specific antibodies

• Sampling easy (milk) to difficult (blood)
• Rapid techniques ? numbers to be examined are
  high
• Sensitivity and specificity may vary according to
  the test
• Serological assays were designed rather as
  qualitative tests for the detection of parasites,
  rather than quantitative tests to estimate the
  level of infection and/or morbidity

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Conclusions

• To determine an economic threshold treatment vs
  non-treatment with the conventional diagnostic
  techniques remains difficult for helminth
  infections.
• The reason for this is not a lack of sensitivity
  or specificity of the available diagnostic
  techniques but
• a lack of studies to determine quantitative
  relationships between diagnostic test results and
  morbidity.

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Objectives presentation

• The factors contributing to morbidity in helminth
  infections of cattle
• The limitations of the existing conventional
  diagnostic techniques
• Innovative parameters for identification of
  animals/herds requiring treatment

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PARASOL
The EU has provided 2.9 Million Euro for a
research project (PARASOL) to investigate and
develop sustainable, low-input methods for
internal parasite control in ruminants. The
project involves 12 academic partners and 5
business ventures from 7 EU countries as well as
Africa.
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What does PARASOL want to achieve?

• To replace current practice with Targeted
  Selective Treatments (TST), where only
  animals/herds showing clinical symptoms or
  reduced productivity are treated.
• To assess several innovative methods, under
  various farming conditions, for identifying
  animals/herds that require treatment
• Challenges are to identify diagnostic parameters
  which are simple, cheap and reliable

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Towards health monitoring

• Adaptation of parasitological control strategies
  which assess the economic losses to targeted
  treatments requires the development of
  parasitological morbidity indicators

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Towards health monitoring

• Samples for analysis should be cheap/easy to
  collect
• Morbidity markers should ideally provide
  information on the
• parasite-associated economic losses
• losses that are recoverable through treatment
• identify control measures to be taken

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Sampling (1)

• Herd health monitoring has become an essential
  part of cattle breeding, requiring samplings at
  regular intervals.
• For cost-effectiveness and animal welfare
  reasons, animal handling to collect samples
  should be restricted to
• the minimum
• non-invasive methods

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Sampling (2)

• In adult dairy cattle, most suitable would be
  diagnostics applied on milk samples
• In FGS calves and beef cattle frequent handling
  of the animals can be avoided by diagnostic tests
  on
• Serum samples collected for established
  surveillance programmes (e.g. brucellosis) ?
  requires an integrated approach by different
  animal health workers
• As sampling during the pasture season may be
  difficult ? sampling at/during housing
• Indicators based on automated weight recordings

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FSG calf
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First season grazing calves

• Modelling/forecasting of infection levels not
  yet a practical option
• Sampling during grazing season difficult
• Measures of morbidity are
• Weight gains (according to breed)
• Pepsinogen as a direct indicator of the clinical
  damage caused by the abomasal worm Ostertagia
  ostertagi.
• Antibodies (Ostertagia) follow a seasonal
  pattern and are a reflection of the amount of
  exposure of the host to the parasite

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Serum pepsinogen levels

• When determined at housing, they are an excellent
  tool to evaluate
• the exposure to GI nematode infection
• the effectiveness of any control programme
• In addition, negative correlations have been
  established between the serum pepsinogen level
  determined at housing and the growth performance
  of calves.

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Interpretatation of pepsinogen levels

• Values lower than 1.5 U tyr
• Intensive control (efficient pasture management
  combined with treatments) with high weight gains
  (gt 750g/day)
• Insufficient contact ? potential for a
  sub-optimal production during second grazing
  season ( 670g)
• Potential selection for AR
• Control programme needs to be optimised

Values over entire grazing season for Holstein
breed, may vary according to country During
first month after turn-out
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Interpretatation of pepsinogen levels

• Values between 1.5 and 3 U tyr
• Adequate control with acceptable weight gains
  (300 - 750g/day)
• Sufficient contact ? optimal production during
  second grazing season ( 1200 g/day )
• Control programme adequate but a yearly
  evaluation necessary

Values over entire grazing season for Holstein
breed, may vary according to country During
first month after turn-out
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Interpretatation of pepsinogen levels

• Values higher than 3 U tyr
• Infection levels too high ? FSG calves may or may
  not show all symptoms of PGE but certainly weight
  gains are low (lt 250g/day)
• Sufficient contact ? optimal production during
  second grazing season ( 1100 g/day )
• Control programme needs to be optimised

Values over entire grazing season for Holstein
breed, may vary according to country During
first month after turn-out
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Serum pepsinogen levels at housing
Chemoprophylactic treated
6
Sub-clinical controls
Clinical controls
4
U tyrosine
2
0
1 2 2 3 4 5 6 7 8 9 10
11 12 13 13 7 14 9 10 10 3 15 16 17
6 15 2 1 18 7 9 11 8 19 14 12
4 20 16 13 3
farms
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Ostertagia antibodies and weight gains

• Ploeger et al (1990) showed that the level of
  exposure
• ( antibody titres against Ostertagia) in the
  first grazing season had a significant positive
  effect on body weights achieved at end of the
  second year

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Dairy Cows
Dairy Cows
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Dairy cows

• The importance of production losses due to
  parasites ?
• The more intensive control during the FGS results
  in lower infection levels ? older animals may be
  more susceptible
• High production levels are incompatible with the
  presence of parasites

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Dairy cows

• The importance of production losses due to
  parasites ?
• Changes in management (e.g. more cows/farm) may
  result in increased risks for infections
• Genetic selection for higher production may have
  resulted in more susceptible animals (?)
• Farmers are becoming more aware about the problem

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Estimates of production losses (helminths)

• Most studies on production losses are related to
  infections with GI nematodes (Ostertagia)
• Prevalence of infection 80-100
• Economical losses in milk production extensively
  documented
• Anthelmintic treatment will result in gt
  2l/day/cow on heavily infected farms
• Limited studies available on Fasciola hepatica
• For Lungworms studies are non-existent

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Diagnosis in bulk milk

• Commercially available
• Fasciola hepatica detects Pherd 25
• Neospora caninum detects Pherd 15
• Hypoderma bovis
• In developing phase
• Dictyocaulus viviparus (Hannover)
• Fasciola hepatica (Gent/Liverpool)
• Ostertagia ostertagi (Gent)
• Others in need to be developed
• Chorioptes

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Gastrointestinal nematodes

• Studies were mainly performed in Canada and
  Belgium to determine
• The associations between Ostertagia-specific
  antibody levels in bulk tank milk and measures of
  productivity and hazard of conception in dairy
  herds
• The use of bulk tank milk ELISA as a promising
  tool to detect dairy herds with
  Ostertagia-associated production losses?

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Ostertagia - Antibody levels

• ODRSPRING
• Mean 0,825
• Interquartile range
• 0,702 to 0,958

• ODRAUTUMN

• Mean 0,972
• Interquartile range
• 0,829 to 1.115

n2553
n2104
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Correlation between OD and milk production
MilkYield
-0.9 kg Milk -1.1 kg Milk
1.115
0.829
ODR
Autumn
0.958
0.702
ODR
Spring
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Fasciola hepatica

• We performed studies in Belgium to determine
• The associations between Fasciola-specific
  antibody levels in bulk tank milk and measures of
  productivity in dairy herds
• The use of bulk tank milk ELISA as a promising
  tool to detect dairy herds with
  Fasciola-associated production losses?

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Antibody levels
ODRf ODRo
n1105
n1077

• Skewed distribution
• Mean 0.762
• 25th-75th percentile 0.428-1.064

• Normal distribution
• Mean 0.443
• 25th-75th percentile 0.334-0.544

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Relationship with milk yield

• Significant linear negative relationship
• Slope -1.10 -1.79 -0.40 (P0.002)
• Increase in ODRf from 25th to 75 th percentile
• Decrease in annual average milk yield of 0.7
  kg/cow/day -1.1 -0.3
• This is equal to 3 of the annual production

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Beef
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Beef cattle

• Weight gains (carcass quality, fertility) are the
  key production parameters
• Many studies showed that regular treatments
  increased production in beef cattle
• Diagnostic parameters ?
• New technologies such as automated weight
  recordings and digital image systems based on
  laser scanning technology may offer new
  perspectives in the use of production parameters.
• OD determinations GI nematodes Fasciola
• ?-GT for Fasciola

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Fasciolosis
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Conclusions (1)

• The main problem of conventional diagnostic
  techniques is the lack of quantitative
  relationships between test results and morbidity
• Progress is made to develop diagnostic morbidity
  markers
• We need tests that include morbidity of several
  parasites as polyparasitism is the rule

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Conclusions (2)

• Even if the relationship of any test values and
  production is known, determining a threshold - to
  treat or not to treat - will always remain
  difficult
• Thresholds may be an idealised concept and are
  not the one size fits all concept because of
  variations in e.g.
• climate/epidemiology/farm management
• importance of production indices
• breed variation in resilience/resistance
• recoverable costs

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Conclusions (3)

• Thresholds may also require different approaches
  depending if e.g.
• group/herd treatment is being contemplated or
• selective treatment of animals within that group 

• It is thus very important to consider thresholds
  rather as guidelines
• The veterinarian should have the last word!

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Thanks Merci Dank