Accepted article

Rev. sci. tech. Off. int. Epiz., 2014, 33 (3), ... - ...
No. 23062014-00036 1/25
Effectiveness of systematic foot and mouth
disease mass vaccination campaigns in
Argentina
This paper (No. 23062014-00036-EN) has been peer-reviewed, accepted, edited, and
corrected by authors. It has not yet been formatted for printing. It will be published in
December 2014 in issue 33-3 of the Scientific and Technical Review.
E.A. León (1)*, A.M. Perez (2), M.A. Stevenson (3), B. Robiolo (4),
N. Mattion (4), C. Seki (4), J. La Torre (4), A. Torres (5), B. Cosentino (6)
& S.J. Duffy (7)
(1) Instituto Nacional de Tecnología Agropecuaria, Centro de
Investigación en Ciencias Veterinarias y Agronómicas, Instituto de
Patobiología, CC25, 1712 Castelar, Argentina & Faculty of Veterinary
Sciences, University of Buenos Aires, Argentina
(2) Department of Veterinary Population Medicine, College of
Veterinary Medicine, University of Minnesota, 385A Animal Science
Veterinary Medicine Building, 1988 Fitch Ave., St. Paul, MN 55108,
United States of America
(3) Epicentre, Room 1.12, Wool Building, Private Bag 11 222,
Massey University, Palmerston North 4442, New Zealand
(4) Centro de Virología Animal, Instituto de Ciencia y Tecnología
Dr. Cesar Milstein, Consejo Nacional de Investigaciones Científicas y
Técnicas, Saladillo 2468, C1440FFX CABA, Argentina
(5) COPROSA, Ministerio de Asuntos Agrarios, Torre
Gubernamental I, Calle 12 y 51 Piso 7, 1700 La Plata, Buenos Aires,
Argentina
(6) Dirección de Epidemiología y Análisis de Riesgo, Dirección
Nacional de Sanidad Anima, Servicio Nacional de Sanidad y Calidad
Agroalimentaria, Paseo Colón 367, C1063ACD CABA, Argentina

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(7) Centro de Estudios Cuantitativos en Sanidad Animal, Faculty of
Veterinary Sciences, National University of Rosario, Boulevard
Ovidio Lagos y Ruta 33, 2170 Casilda, Santa Fe, Argentina
*Corresponding author: [e-mail]
Summary
The objective of this paper is to evaluate the effectiveness of
systematic mass vaccination campaigns against foot and mouth
disease in Argentina. The analysis was based on an estimation of the
proportion of protected animals and protected farms in vaccinated
populations, as reflected by levels of antibodies measured in liquid-
phase enzyme-linked immunosorbent assay. The analysis was carried
out in 42 animal health districts in Buenos Aires province, using data
collected from four cross-sectional studies, in 2004, 2007, 2008 and
2011. Cattle were assigned to one of two categories on the basis of
correlation between serological titres and expected percentage
protection: non-adequately protected (expected protection <75%) and
adequately protected (expected protection 75%). The proportions of
adequately protected cattle and significantly non-adequately protected
farms were estimated and compared among sampled locations.
Protection was variable among the districts; cattle aged one to two
years showed higher levels of protection than cattle six to 12 months
old, and the proportion of protected cattle was higher in the more
recent studies. The results of the analysis will allow the national
animal health service to investigate in depth those districts where
protection was lower than the regional background protection. The
authors propose that this methodology could be used to evaluate the
effectiveness of vaccination campaigns in other countries or zones
where systematic foot and mouth disease mass vaccination campaigns
are undertaken.
Keywords
Adequately protected animal – Evaluation of vaccination campaign –
Foot and mouth disease – Liquid-phase blocking ELISA – Mass

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vaccination campaign – Sampling design – Significantly non-
adequately protected herd.
Introduction
Foot and mouth disease (FMD) is arguably one of the most contagious
infectious diseases of mammals and has great potential for causing
severe economic loss in susceptible cloven-hoofed animals. There are
seven serotypes of FMD virus (FMDV); namely, O, A, C, SAT 1,
SAT 2, SAT 3 and Asia 1, incorporating a large and indeterminate
spectrum of subtypes. Typical cases of FMD are characterised by a
vesicular condition of the feet, buccal mucosa and, in females, the
mammary glands; clinical signs may vary from mild to severe and
fatalities may occur, especially in young animals (1). Infection or
vaccination with one FMDV serotype does not confer immunity
against another serotype, and the protection conferred by one subtype
against another subtype of the same serotype is variable, ranging from
none to complete (2).
A number of South American countries are exporters of animals and
animal products derived from FMD-susceptible species; such products
have the potential to carry the virus. Importing countries implement
strict health barriers in this international trade and it is a priority for
exporter countries to preserve their FMD-free status. The virus
persists in some parts of the South American continent (3, 4) and
outbreaks have been recently reported in Ecuador (2006 to 2011) and
Venezuela (2007 and 2011) (5). In addition, during recent years
clinical cases have been sporadically detected in FMD-free countries
and zones such as Argentina (2006), Brazil (2006), Bolivia (2007),
Colombia (2008 and 2009) and Paraguay (2011 and 2012) (6).
Consequently, most South American animal health services have
designed and implemented compulsory systematic FMDV mass
vaccination programmes for cattle at the whole-country level or at
zone level. The ultimate objective of such programmes is to raise herd
immunity to the level that prevents the introduction of FMDV or
mitigates its spread within the susceptible population.

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The FMDV vaccine currently used in Argentina is oil-adjuvanted and
tetravalent, comprising strains A24/Cruzeiro, A/Argentina/2001,
O1/Campos and C3/Indaial (7). To be approved for general use, each
batch of vaccine is subject to tests for safety and potency by the
national animal health service (Servicio Nacional de Sanidad y
Calidad Agroalimentaria [SENASA]) (8). The vaccination
programme is administrated by SENASA for the entire territory, with
the exception of Patagonia, which is recognised by the World
Organisation for Animal Health (OIE) as an FMD-free zone where
vaccination is not practised. Vaccination takes place twice per year,
although other strategies such as annual vaccination are used in very
limited and isolated areas. Only cattle are vaccinated and each
campaign lasts approximately two months. In any given year, all cattle
(independently of age) are vaccinated in the first campaign, and then
cattle under two years of age are vaccinated in the second campaign.
The vaccination area contains more than 95% of the country’s cattle
population.
The operational aspects of the vaccination campaign, including its
design and the purchase, storage and delivery of the vaccines, are
coordinated by SENASA-audited local authorities in each animal
health district. Each district is administered by an elected group of
producers, has a defined geographical area under its mandate and has
a veterinarian as technical director. Vaccination is administered by
contracted personnel. Throughout Argentina there are 305 animal
health districts with a total of approximately 220,000 cattle producers
and 50 million cattle.
The effectiveness of a vaccination programme depends on a number
of factors (9, 10). First, the vaccine should be of adequate potency and
safety, should contain strains of FMDV that match field strains, and
should be subjected to a modern quality assurance system, according
to the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial
Animals, Chapter 2.1.5. (1). In addition, the vaccine should be stored
and distributed under proper conditions, using a cold chain, and the
shelf life of the product should not be exceeded. Secondly, the interval
between vaccination events on a single farm, the age of the calves at

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first vaccination and the duration of the vaccination campaign should
be consistent with the expected pattern of natural and artificial
immunity. The level of vaccination coverage that is required depends
on several factors and it is impossible to be prescriptive; however, the
aim should be to achieve at least 80% herd immunity (11). Lastly, the
vaccine should be used according to the procedure prescribed by the
manufacturer. Failure to achieve and control compliance with these
factors contributes to the maintenance of FMDV circulation, even in
countries where the main control strategy has been massive
vaccination over a number of years (12).
Post-vaccination monitoring is necessary for estimating FMD
protection at the level of both the individual animal and the farm, and
for identifying possible campaign failures (13). The objective of this
study was to design and apply an analytical method for evaluation of
the effectiveness of systematic FMDV mass vaccination campaigns.
The method was used to evaluate the effectiveness of a mass
vaccination programme in Argentina.
Materials and methods
Sampling frame
The province of Buenos Aires covers approximately 300,000 km2.
Within the province there are 105 animal health districts that manage
the vaccination of approximately 20 million cattle distributed on
approximately 60,000 livestock farms. Approximately 40% of
Argentina’s cattle population is located within the province of Buenos
Aires.
Sampling design
Four independent cross-sectional studies were carried out in 2004,
2007, 2008 and 2011. In each of them, the animal health districts were
enrolled on a voluntary basis. A two-stage, random-sampling design
was used to estimate the proportion of cattle protected against FMD
per farm in each district. In the first stage, farms (primary sampling
units) were selected with a probability of selection proportional to the