1 

 

Ministry of Production 

Secretariat of Agriculture, Livestock, Fisheries 

 and Food 

National Service for Agrifood Health and Quality 

SENASA 

ANNEX 

FMD SERO-EPIDEMIOLOGICAL SURVEILLANCE 

SEROLOGICAL SAMPLING 2005-2006 

NATIONAL DIRECTORATE FOR ANIMAL HEALTH 

EPIDEMIOLOGY DIRECTORATE 

ARGENTINA 

January 2007
2 

INTRODUCTION: 

FMD epidemiological surveillance implemented by SENASA is in line with Animal 

Health World Organization (OIE) recommendations to evidence an area is free of the 

disease (Annex 3.8.7 – Guidelines for FMD Surveillance). 

Sero-epidemiological surveillance is conducted annually to prove lack of viral 

circulation or infection, whether in zones with or without vaccination. In addition, 

immunity level conferred through vaccination is estimated in zones where vaccination 

is practiced. 

The Epidemiology Office, reporting to SENASA’s Animal Health Directorate, is 

responsible for survey layout, within the scope of the Epidemiology Advisory 

Committee. The latter is a body formed by epidemiologists from other research 

institutions (INTA, CONICET and Schools of Veterinary Sciences). 

Samples are taken and shipped by SENASA local veterinarians and regional 

supervisors and processed at the Animal Laboratory, reporting to SENASA’s 

Laboratories and Technical Control Directorate (DILAB). 

SAMPLING LAYOUT 

According to OIE recommendations for demonstrating FMD freedom in zones or 

countries with or without vaccination, sero-epidemiological sampling is implemented 

in two stages, namely: 

- a statistically-designed initial sampling, which comprises all agricultural 

exploitations of the country, and 

- an additional sampling (along with other investigations) in farms where 

animals reacting to the initial sampling were found. The purpose of 

additional sampling is to confirm or rule out the first result. 

1. Objective: 

a) Detecting viral circulation or infection by FMD virus (FMDV) throughout the 

Argentine Territory. 

b) Estimating immunity level of cattle population in areas where vaccination 

against FMD is practiced. 

2. Variables to be measured: 

2.1 Presence of antibodies against FMDV non-capsidal proteins in vaccinated 

animals and antibodies against structural proteins (SP) in non-vaccinated animals, as 

indicator of viral infection or circulation. 

2.2. Antibody titres against FMDV structural proteins in vaccinated cattle, as indicator 

of population immunity level. 

3. Sampling framework: 

3.1. Sampling comprises all livestock farms registered in the National Health Register 
3 

of Agricultural Producers (RENSPA) throughout the country. In order to adjust 

sampling objectives to different epidemiological situations, the country was divided 

into zones, according to the following parameters: 

- Animal density 

- Composition of cattle population(steer/cow ratio). 

- Animal movements (movements in and out). 

- Geographical and political-administrative characteristics. 

- Effectiveness of vaccination rounds 

- Risk areas (border areas). 

- Surveillance zones (in free areas) 

- Results of previous serological samplings 

Zones detailed below were determined following these criteria (see Map 1): 

1. Central-Mesopotamia and NOA-Cuyo 

2. Fattening 

3. Border 

4. Northern A Patagonia 

5. Northern B Patagonia 

6. Southern Patagonia 
4 

Map 1: Zoning 

4. Animals and categories sampled: 

Criteria for selecting species to be sampled in each zone were preponderance of 

each susceptible species as well as sampling effectiveness. 

In areas with vaccinated cattle, the bovine species was chosen due to its 

preponderance and also for practical purposes, since sampling was conducted at the 

same time of vaccination. 

In areas without vaccination, sheep/goat were chosen due to their preponderance. 

4.1. Cattle: the following categories were sampled in all zones, except for Southern 

Patagonia region. 

- Category 1: 6 to 12 months old. 
5 

- Category 2: 12 to 24 months old. 

4.2. Sheep/goats: of any category and age; samples were taken only in Southern and 

Northern B Patagonia regions. 

All sampled animals were identified with official numbered tags (snap button tag). 

5. Estimation of sample size: 

Sampling is conducted in two stages. Herd number, from which samples are 

to be taken (Formula No1), is calculated first, and then the number of individuals per 

herd (formula No2). 

Formula No 1: Number of herds required (nr) 

( ) 



 



 − × − 



 



 = − − 2

1 1 1

1 e

n NC Nr e r

Where 

NC Confidence level (to detect at least one positive animal within the population) 

e Number of affected herds that may be detected as such within the population. 

This value is obtained by multiplying number of herds within the population to be surveyed 

(Nr) by expected prevalence of positive herds and by confidence level to be established to 

determine number of individuals to be sampled per herd. 

Nr Number of herds within the population to be surveyed 

Formula N°2: Number of individuals to be sampled per herd (ni): 

( ) 



 



 − × − 



 



 = − − 2

1 1 1

1 e

n NC Ni e i

Where 

NC Confidence level (to detect at least one positive animal per farm) 

e Number of individuals within the event that may be detected per herd. This value is 

obtained by multiplying number of individuals per herd (Ni) by detectable prevalence, 

which is the result of the product between expected prevalence (p) and sensitivity (Se) of 

diagnostic method (N * p * Se) 

Nr Average number of individuals per herd 

Note: assumptions used vary from one zone to another, as explained below. 
6 

6. Layout for viral circulation per zone: 

6.1. Central- Mesopotamia and NOA-Cuyo zones: 

It is comprised by Central, Mesopotamia, NOA and Cuyo regions set out in the FMD 

Eradication Plan 2001, except for the locations included in Fattening and Border 

zones. 

Assumptions to detect viral activity within this zone were made taking into account 

historic behavior of FMD in this region and data obtained from latest samplings, 

namely: 

- Prevalence of infected farms: 1% 

- Prevalence within the farm : 10% 

- Confidence level: 95% 

On the basis of these assumptions, 313 farms should be selected and 28 animals 

should be sampled in each farm, totaling 8764 samples. 

Species and categories to be sampled: 

28 bovines from each farm, namely: 

- 17 of Category 1 (6 to 12 months old) 

- 11 of Category 2 (12 to 24 months old) 

Note: For 2006 sampling plan, samples were also taken from 10 (ten) sheep/goat, from 12 to 24 

months old, from the selected farm or an adjoining farm (when such species is not present in the 

selected farm). 

6.2. Fattening zone: 

This zone is formed by northwestern districts of Buenos Aires, northeastern districts 

of La Pampa and southern districts of Córdoba, Santa Fe and Entre Ríos. 

Districts involved are detailed below: 

a) Buenos Aires province: C. Casares, C. Tejedor, Colón, Daireaux, Gral. Arenales, 

Gral. Pinto, Gral. Villegas, Guaminí, H. Irigoyen, L.N. Alem, Lincoln, Pehuajó, C. 

Pellegrini, Rivadavia, Salliquelló, T. Lauquen, Tres Lomas and Ameghino. 

b) Santa Fe province: Caseros, Constitución, Gral. López, Rosario y San Lorenzo. 

c) Córdoba province: Gral. Roca, R.S. Peña and Rio Cuarto. 

d) La Pampa province: Capital, Catriló, Conhelo, Chapaleufú, Maracó, Q. Quemú, 

Rancul, Realicó and Trenel. 

e) Entre Rios province: Gualeguay, Gualeguaychú, Islas del Ibicuy and Victoria. 

Assumptions for detection of viral circulation within this zone, for 2005, are given 

below: 

- Prevalence of infected farms: 1% 

- Prevalence within the farm: 20% 

- Confidence level 95% 
7 

Estimation of prevalence within the farm was higher than in other regions (20%) due 

to production characteristics of this zone, which presents a high contact rate among 

young animals. 

On the basis of these assumptions, 313 farms should be selected and 14 animals 

from each farm should be sampled (4.382 samples). 

Species and categories to be sampled: 

14 bovines from each farm, namely: 

- 9 of Category 1 (6 to 12 months old) 

- 5 of Category 2 (12 to 24 months old) 

Assumptions for detection of viral circulation within this zone, for 2006, are given 

below: 

- Prevalence of infected farms: 1% 

- Prevalence within the farm: 15% 

- Confidence level 95% 

Estimation of prevalence within the farm was higher than in other regions (15%) due 

to production characteristics of this zone (high contact rate plus predominance of 

young animals). 

On the basis of these assumptions, 313 farms should be selected and 19 animals 

from each farm sampled (5.947 samples). 

Species and categories to be sampled: 

19 bovines from each farm, namely: 

- 12 of Category 1 (6 to 12 months old) 

- 7 of Category 2 (12 to 24 months old) 

Note: For 2006 sampling plan, samples were also taken from 10 (ten) sheep/goat, from 12 to 24 

months old, from the selected farm or an adjoining farm (when no sheep/goat was present in the 

selected farm). 

6.3. Border zone: 

This zone is formed by districts of Jujuy, Salta, Formosa, Chaco, Corrientes and 

Misiones provinces located next to the border with Bolivia and Paraguay. It includes 

the 25-km strip of land comprised in the Subproject Northern “A” Border. Sampling 

conducted in this zone is part of additional surveillance actions implemented in risk 

border areas. 

Assumptions for detection of viral circulation within this zone are given below: 

- Prevalence of infected farms: 1% 

- Prevalence within the farm: 10% 

- Confidence level 95% 

On the basis of these assumptions, 313 farms should be selected and 28 animals 

should be sampled (8.764 samples). 

Species and categories to be sampled: 
8 

28 bovines from each farm, namely: 

- 17 of Category 1 (6 to 12 months old) 

- 11 of Category 2 (12 to 24 months old) 

Note: For 2006 sampling plan, samples were also taken from 10 (ten) sheep/goat, from 12 to 24 

months old, from the selected farm or an adjoining farm (when no sheep was present in the selected 

farm), provided they were never vaccinated since in the zone comprised in Subproject 

Northern A Border sheep/goats are also vaccinated systematically. 

6.4. Northern “A” Patagonia: 

This zone is formed by the area of Río Negro province where vaccination against 

FMD is practiced (north to Río Negro river) and the district of Patagones, in Buenos 

Aires province (according to FMD Eradication Plan 2001). 

Assumptions for detection of viral circulation within this zone are given below: 

- Prevalence of infected farms: 1% 

- Prevalence within the farm: 15% 

- Confidence level 95% 

Due to a relatively smaller size of this zone, as compared to the rest of the zones, the 

layout could be adjusted to the number of farms conforming the zone (3.500). 

On the basis of these assumptions, 300 farms should be selected and 19 animals 

should be sampled (totaling 5.700 samples). 

Species and categories to be sampled: 

19 bovines from each farm, namely: 

- 12 of Category 1 (6 to 12 months old) 

- 7 of Category 2 (12 to 24 months old) 

Note: For 2006 sampling plan, samples were also taken from 10 sheep/goat, from 12 to 24 months 

old, from the selected farm or an adjoining farm (when no sheep/goat was present in the selected 

farm). 

6.5. Northern “B” Patagonia: 

For 2005 

This zone corresponds with Northern “B” Patagonia region, laid down in the FMD 

Eradication Plan 2001. It comprises the areas of Río Negro and Neuquén provinces 

where vaccination against FMD is not practiced. 

Samples were taken from bovines and sheep/goats. 

Assumptions for detection of viral circulation are the following: 

- Prevalence of infected farms: 1% 

- Prevalence within the farm: 10% 

- Confidence level 95% 
9 

On the basis of these assumptions, 313 farms should be selected and 28 samples 

taken from each farm (totaling 8764 samples). 

Species and categories to be sampled: 

 In farms with bovines and sheep/goats, samples should be taken from: 

- bovines: 11 animals from Category 1 (6 to 12 months old) 

7 animals from Category 2 (12 to 24 months old) 

- sheep/goats: 10 animals of whichever category and age. 

 In farms with bovines only, samples should be taken from: 

- 17 animals from Category 1 (6 to 12 months old) 

- 11 animals from Category 2 (12 to 24 months old) 

 In selected farms with sheep/goats only, samples should be taken from 28 

animals of whichever category and age. 

6.6. Southern Patagonia: 

For 2005 

This zone corresponds with Southern Patagonia region, laid down in the FMD 

Eradication Plan. It comprises the provinces of Chubut, Santa Cruz and Tierra del 

Fuego, Antártida e Islas de Atlántico Sur. 

Only sheep are sampled in this zone. 

Assumptions for detection of viral activity are the following: 

- Prevalence of infected farms: 1% 

- Prevalence within the farm: 10% 

- Confidence level 95% 

On the basis of these assumptions, 313 farms were selected and 28 samples taken 

from each farm. (Totaling 8764 samples). 

Species and categories to be sampled: 

28 sheep of whichever category and age from each farm.

 6.7 Northern B and Southern Patagonia 

For 2006 

Both zones were gathered taking the same assumptions, species and categories 

given for Northern B Patagonia in the 2005-sampling plan. 

The table below summarizes assumptions used in each zone and number of farms 

and animals to be sampled according to the layout. 
10 

Table N°1a: Number of farms and animals to be sampled per zone, 2005. 

Samples 

ZONE Farm 

prev. 

Prev. 

within 

farm 

N° farms 

to be 

sampled Per 

farm 

Total 

Zone 

Species 

Central-Mesop. 

and NOA-Cuyo 1% 10 % 313 28 8764 Bovine 

Fattening 1% 20 % 313 14 4382 Bovine 

Border 1% 10 % 313 28 8764 Bovine 

Northern A 

Patag. 1% 15 % 300 19 5700 Bovine 

Northern B 

Patag. 1% 10 % 313 28 8764 Bovine and sheep/goat 

Southern 

Patagonia 1% 10 % 313 28 8764 Sheep/ goat 

TOTAL 1865 45.138 

Table N°1b: Number of farms and animals to be sampled per zone, 2006. 

Cattle samples Sheep samples 

ZONE Prev. 

Farms 

Prev. 

within 

farm 

N farms 

Per 

farm 

Total 

zone 

Per 

 farm 

Total 

zone 

CentralMesopotamia and 

NOA-Cuyo 

1% 10 % 313 28 8764 10 3130 

Fattening 1% 15 % 313 19 5947 10 3130 

Border 1% 10 % 313 28 8764 10 3130 

Northern A 

Patagonia 1% 15 % 300 19 5700 10 3130 

Northern B and 

Southern 

Patagonia 

1% 10 % 313 18* 5634 10* 3130 

TOTAL 1.552 34.809 15.650 

* Variable according to animal stock of selected farm 
11 

7. Diagnostic tests: 

7.1. Detection of viral circulation: 

Bovines: ELISA 3ABC-EITB (PANAFTOSA, PHO-WHO kit) diagnostic system 

was used to detect Ab against FMDV non-capsidal proteins, in areas 

subjected to systematic vaccination, and ELISA fl (CEVAN-CONICET kit) for 

detecting Ab against structural proteins against virus types A2001 and O1

Campos in areas without vaccination (Northern B Patagonia). 

Sheep/goats: in these non-vaccinated species measurement of Ab against 

FMDV structural proteins was conducted applying lp ELISA for virus types A 

2001 and O1 Campo. 

7.2. Estimation of immunity level: In 2005, Elisa Lp was used to measure Ab 

against FMDV structural proteins for virus types A 2001 and O1 Campo; 

strain C3 Indaial being added in 2006 (CEVAN-CONICET Kit). 

8. Farms sampled 

Farms sampled were chosen at random by a random drawing conducted at central 

level (Epidemiology Directorate). Sampling framework was given by Health 

Management System (SGS) database containing updated information on all farms 

registered in the RENSPA. 

9. Sampling schedule 

In zones where vaccination against FMD is practiced sampling was conducted along 

with the first vaccination round. 

In zones where such vaccination is not carried out, animals were sampled from 

February to May. 

10. Additional sampling: 

According to OIE Guidelines for the surveillance of foot and mouth disease (Annex 

3.8.7 of the Code) subsequent investigations and additional sampling were 

conducted in all farms where at least one bovine serum was reactive to ELISA 

3ABC/EITB or lp ELISA in sheep/goat during the first sampling. 

Said investigation included the following: 

10.1 Another visit to the farm, epidemiological questioning to its owner or 

person responsible of animals thereat, survey on last year’s movements 

of susceptible animals and clinical inspection of all animals in the farm. 

10.2 Additional sampling. New blood samples were taken after clinical 

inspection of the following animal groups: 

10.2.1 Animals bled in the first sampling (initial sampling), after at least 30 

days of first sampling had passed. 

10.2.2 “Contact” lot. 60 bovines from 6 to 12 months old belonging to a lot that 

was in “contact” with the group of animals initially sampled, whether 

from the same premises or adjoining premises. 
12 

10.2.3 Non-vaccinated FMD susceptible animals. Up to 60 sheep or goats 

from the reactive holding or an adjoining holding. 

10.3 Probang: two esophageal-pharyngeal liquid samples for Probang 

testing were taken from reactive animal(s), at a minimum interval of 21 

days in between. 

11. Estimation of population immunity 

Population immunity was assessed using the same samples taken to estimate viral 

circulation, by taking a random sub-sample. Assumptions to determine the size of 

this sub-sample were based on estimations for expected immunity level of category 1 

animals (with lower number of vaccinations applied): 

- Expected proportion of animals covered: 65% 

- Acceptable Error: 10% 

- Confidence level: 95% 

On the basis of these assumptions, 120 farms were randomly chosen from Central 

Mesopotamia and NOA/Cuyo zone, which were no reactive to ELISA 3ABC/EITB 

system, and 100 farms from the remaining zones. Out of each farm, 13 cattle 

samples were chosen at random from the following categories: 

- 10 from category 1 (6 to 12 months old) 

- 3 from category 2 (12 to 24 months old) 

12. Results 

 12.1 Results of viral circulation for 2005 

 

 Results of initial sampling conducted in areas where vaccination is practiced are 

shown in Table 2 below. 

Table 2: Results of initial sampling of cattle to detect viral circulation in zones where 

vaccination is practiced, per zone and category. 

 Category 1 Category 2 

Reactive 

farms Reactive Reactive 

Zone Analysed 

farms 

n % 

N 

n % 

N 

n % 

Central –

Mesop/NOA-Cuyo 305 10 3,3% 4936 4 0,08% 3038 9 0,3% 

Fattening 290 8 2,8% 2460 1 0,04% 1417 8 0,6% 

Border 301 9 3,0% 4633 5 0,11% 2966 11 0,4% 

Northern A 

Patagonia 311 6 1,9% 3673 8 0,22% 2123 2 0,1% 

TOTAL 1207 33 2,7% 15702 18 0,11% 9544 30 0,3% 
13 

Map 2: Distribution of (cattle) farms sampled per zone for 2005 
14 

Results for viral circulation according to initial sampling conducted in zones without 

vaccination (Northern B and South Patagonia) are detailed in Table 3 below. 

Table 3: Results of initial sampling 2005 in zones without vaccination. 

Farms Bovine serum Sheep/ 

Zone goat serum 

Analysed Reactive Analysed Reactive Analysed Reactive 

Northern 

B Patag. 318 0 2231 0 6324 0 

Southern 

Patag. 317 0 0 0 9044 0 

TOTAL 635 0 2231 0 15368 0 

Follow-up of reactive farms: 

Farms where at least one animal reacted to ELISA 3ABC/EITB system in the initial 

sampling (33) were subjected to further investigation, pursuant to Annex 3.8.7 of the 

Code, Guidelines for FMD Surveillance. 

A detail of farms investigated and samples taken during additional sampling is given 

in the following table. In some cases, sampling was also conducted in premises next 

to the reactive farm. Therefore, total farm number (38) is higher than reacting farms 

(33). 

Table 4: investigated farms, samples taken and results of additional sampling. 

Zone No reactive 

farms 

No sampled 

farms 

Bovine 

samples 

taken 

Reactive 

bovine 

samples 

Sheep/goat 

samples 

taken 

Reactive 

sheep/goat 

samples 

Central –

Mesop. / 

NOA-Cuyo 

10 12 528 3 207 0 

Fattening 8 8 339 0 73 0 

Border 9 10 560 0 60 0 

Northern A 

Patagonia 6 8 344 1 69 0 

Total 33 38 1771 4* 409 0 

*Each one from different premises. 
15 

Map 3: distribution of farms presenting reactive sera in first sampling 2005 
16 

All farms were visited and animals therein inspected. Additional serum samples were 

taken in 32 out of 33 reactive farms to rule out or confirm initial sampling results. 

Re-sampling could not be carried out in one farm due to depopulation of the farm at 

the time of the visit. EPL samples were taken for Probang testing, from which no 

virus was recovered. 

Out of animals that reacted in the initial sampling, only one (1) remained reactive. 

Sero-conversion was not detected in any case. No evidence of epidemiological risk 

was found after activities previously mentioned (clinical inspection, movement survey, 

epidemiological questioning, etc.) were carried out in such premises. 

 12.2 Results of viral circulation for 2006 

 

12.2.1 Initial sampling 

Results of initial sampling in cattle are given in Table 5 below. 

Table 5. 2006 results of initial sampling in cattle to detect viral circulation/infection, per zone 

and category. 

Category 1 Category 2 

Reactive farm Reactive Reactive 

Zone Analysed 

farm 

n % 

N 

n % 

N 

n % 

Central –

Mesop/NOACuyo 284 3 1,06% 4431 2 0,05% 2977 3 0,10% 

Fattening 286 4 1,40% 3306 1 0,03% 1967 3 0,15% 

Border 271 1 0,37% 4172 0 0,00% 2709 1 0,04% 

Northern A 

Patagonia 303 0 0,00% 3459 0 0,00% 2091 0 0,00% 

Northern B and 

Soutnern 

Patagonia 

74 0 0,00% 832 0 0,00% 669 0 0,00% 

TOTAL 1218 8 0,68% 16200 3 0,02% 10413 7 0,07% 
17 

Table 6 below provides results of viral circulation/infection in sheep (non-vaccinated 

species) per zone. 

Table 6. results of initial sampling in sheep to detect viral activity, per zone 

Predios 

reactivos Reactivos 

Zone 

Predios con 

ovinos 

analizados n % 

Muestras 

analizadas 

n % 

Central –

Mesop/NOA-Cuyo 199 0 0 1952 0 0 

Fattening 162 0 0 1562 0 0 

Border 56 0 0 494 0 0 

Northern A 

Patagonia 122 0 0 1186 0 0 

Northern B and 

Soutnern 

Patagonia 

295 0 0 7408 0 0 

TOTAL 834 0 0 12602 0 0 

Comments: As shown in Table 5, out of a total of 1218 (0.65%) premises where 

cattle was sampled only 8 premises had, at least, one reactive animal. Distribution of 

such premises among zones is not even, predominating in CentralMesopotamia/NOA-Cuyo (3 premises) and Fattening (4 premises) zone. However, 

the number is low and no clusters were observed. 

All sheep samples were no reactive. 

12.2.2 Follow-up of positive cases 

Additional investigations were conducted at the 8 premises where at least one 

reactive animal was found, which included: 

12.2.2.1 Epidemiological surveys 

After assessment of these surveys, no risk situations were detected from which it 

could be inferred disease occurrence in premises under investigation. 

 

12.2.2.2 Clinical inspection 

No evidence of FMD or FMD-compatible disease was found. 

12.2.2.3 Additional sampling 

Additional sampling was conducted in all premises involved. Animals from adjoining 

premises were included in cases where they were in-contacts of the reactive lot. 

Table 7 below provides detailed information on samples taken for the additional 

sampling and results obtained. 
18 

Table 7: Detailed additional sampling. 

 Samples taken Reactive samples 

Premises Cattle Sheep/goat Cattle Sheep/goat 

1 60 0 0 0 

2 66 0 0 0 

3 58 34 1 0 

4 50 25 0 0 

5 60 0 0 0 

6 75 45 1 0 

7 73 46 1 0 

8 88 27 0 0 

EFL-Probang samples were taken from 7 (out of 10) reactive animals in the initial 

sampling, no virus being isolated. The other 3 reactive animals were not available at 

the time the farm was visited. 

As shown in the table, only 3 cattle sera were reactive. Only one mantained the same 

result as in the initial sampling. 

12.3 Analysis of sampling results for viral circulation/infection 

- Samplings were conducted as established in the layout 

- Due to space distribution of farms with reactive animals, particular studies for 

clusters were not required. 

- Proportion of farms having at least one reactive animal, between zones, was 

homogeneous. 

- Upon follow-up of premises with reactive animals, no evidence of viral circulation 

was found. 

- No sample was reactive within the zone where vaccination is not practiced 

(Southern and Northern B Patagonia), confirming the “FMD-free without 

vaccination” condition. 

Conclusion: results obtained in this study provide reliable evidence supporting lack of 

viral circulation/infection in zones under study. 

12.4 Population immunity 

12.4.1 Interpretation of results 

According to LP ELISA titre obtained for each serum, immunity level was classified 

into the following categories: Low, Medium or High, on the basis of percentage 

protection expectancy (PPE) for each titre and serotype under study. PPE was 

calculated by correlating lp ELISA titres with Podal Generalization Protection (PGP). 

Ranges for each category are given in the table below. 
19 

Table 8: Interpretation of liquid phase (lp) ELISA results according to PPE. 

Lp ELISA. titre 

O1Campos A2001 PPE RESULT 

< 1.77 < 2.1 < 75% Low 

1.77 – 1.91 2.1 – 2.3 75% a 85% Medium 

> 1.91 > 2.3 > 85% High 

Animals with PPE equal or over 75% had suitable protection levels against natural 

exposure to FMDV. Therefore, and for better understanding the results, categories 

Medium and High were grouped as Medium-High. 

 

Population immunity was assessed with sera obtained at the time prior to revaccination, being the basal protection level of the cattle herd (i.e. worst immunity 

condition). 

Only population immunity results for 2005 are given since at the time this report was 

prepared, data for 2006 was not yet available. NCP tests concluded recently. 

Results: 

The following graphs provide detailed results for population immunity obtained in 

2005 sampling plan. Results are expressed as percentage of sera with Medium-High 

immunity level for each category, zone and virus type. 

Inmunidad Poblacional 2005.

Categoría 2 Virus A 2001

0,00%

20,00%

40,00%

60,00%

80,00%

100,00%

CM/NC Engorde Frontera PatagNor teA

Inm unidad Poblacional 2005. 

Cate goría 2 Virus O1

0,00%

20,00%

40,00%

60,00%

80,00%

100,00%

CM/ NC Engorde Frontera PatagNor teA
20 

Inm unidad Poblacional 2005.

 Categoría 1 Virus A2001

0,00%

20,00%

40,00%

60,00%

80,00%

100,00%

CM/ NC Engor de Fr onter a PatagNor teA

Inm unidad Poblacional 2005.

 Categoría 1 Virus O1

0,00%

20,00%

40,00%

60,00%

80,00%

100,00%

CM/ NC Engor de Fr ont er a PatagNor teA

Percentage of sera with medium-high PPE is satisfactory in all zones. 

Lowest values were found in border zone, in category 1 for virus type A 2001. Such 

titres reflect the maximum drop in the immunity curve of previous vaccination and are 

prior to immediate revaccination. 

To compare data from previous samplings, graphs show results of the last three 

annual samplings (2003 to 2005) together. Please note that for sampling 2005, 

Central/Mesopotamia and NOA / Cuyo zones were unified. The bar for 2003 and 

2004 belong to Central / Mesopotamia zone, since most sera taken during 2005 

originated in that zone. 
21 

Graphs of compared population immunity for 2003, 2004 and 2005 per zone, category and virus 

type. 

By comparing results for 2003-2004 and 2005, a progressive increase of the 

proportion of animals with medium-high PPE is observed in category 1, which could 

reflect improvements in vaccination strategies. 

Conclusions: 

Population immunity levels are satisfactory and compatible with good vaccinal 

coverage, enough to prevent FMDV circulation and transmission. 

Inm unidad Poblacional Comparada

2003, 2004 y 2005. Categoría 2 Virus O1

0,00%

10,00%

20,00%

30,00%

40,00%

50,00%

60,00%

70,00%

80,00%

90,00%

100,00%

2003

2004

2005

Inm unidad Poblacional Comparada

2003, 2004 y 2005. Categoría 1 Virus A2001

0,00%

10,00%

20,00%

30,00%

40,00%

50,00%

60,00%

70,00%

80,00%

90,00%

100,00%

Cent ral –

Mesop

Engor de Fr onter a Pat agNor teA

2003

2004

2005

Inm unidad Poblacional Comparada

2003, 2004 y 2005. Categoría 1 Virus O1

0,00%

10,00%

20,00%

30,00%

40,00%

50,00%

60,00%

70,00%

80,00%

90,00%

100,00%

2003

2004

2005

Inm unidad Poblacional Comparada

2003, 2004 y 2005. Categoría 2 Virus A 

2001

0,00%

10,00%

20,00%

30,00%

40,00%

50,00%

60,00%

70,00%

80,00%

90,00%

100,00%

2003

2004

2005