EDITORIAL

STUDIES ON WILDLIFE WITH A SPECIAL REFERENCE TO PREVENTING

EMERGING INFECTIOUS DISEASES (EIDs) IN THE 21st CENTURY

ESTUDIOS EN FAUNA SILVESTRE PARA PREVENIR ENFERMEDADES

INFECCIOSAS EMERGENTES EN EL SIGLO XXI

Alfonso Marzal

1Departamento de Anatomía, Biología Celular y Zoología, Universidad de Extremadura, Avda. de Elvas s/n, E-06006

Badajoz, Spain.

Correspondence to AM: Tel: (+34) 924289412

E-mail: amarzal@unex.es

Neotropical Helminthology, 2015, 9(2), jul-dec: 199-202.

ABSTRACT

Keywords: deforestation - invasive species - malaria - parasites- emerging infectious diseases.

Emerging Infectious Diseases (EIDs) represent a serious threat for the health of humans, wildlife

and livestock. These diseases are caused by pathogens that have evolved multi-resistance against

medications, or have increased their host and / or geographical range. As a result, millions of

people have died in the last decades because emerging and re-emerging diseases such as malaria,

tuberculosis and Ebola haemorrhagic fever. Socio-economic factors (e.g. urbanization,

demographic factors) and environmental drivers, e.g., deforestation, invasive species and

anthropogenic land use change, have facilitated the spread of EIDs. Many studies have focused

on these diseases in the last half-century. Our understanding of epidemiology of EIDs and how to

control their spread remains limited. Because wildlife is an essential component in the

epidemiology of many EIDs, the study of pathogens in wildlife will be essential to identify

underlying causes and to successfully develop policies and strategies to mitigate these threats.

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ISSN Versión impresa 2218-6425 ISSN Versión Electrónica 1995-1043

RESUMEN

Palabras clave: deforestación, especies invasoras, malaria, parasites.

Las Enfermedades Infecciosas Emergentes (EIDs) son una grave amenaza para la salud de

humanos, animales domésticos y fauna silvestre. Estas enfermedades son causadas por

patógenos que han desarrollado multi-resistencia frente a medicamentos, o han incrementado su

rango geográfico o de hospederos. Como resultado, millones de personas han muerto en las

últimas décadas debido a enfermedades emergentes y re-emergentes como la malaria, la

tuberculosis o las fiebres hemorrágicas del Ébola. Factores socio-económicos (e.g. urbanización,

crecimiento demográfico) y ambientales (deforestación, especies invasoras y cambios en el uso

del suelo producidos por el hombre) han facilitado la dispersión de las EIDs. A pesar de que

muchos estudios se han centrado en estas enfermedades en el último medio siglo, nuestro

conocimiento sobre la epidemiología de las EIDs y cómo controlar su dispersión es aún limitado.

Debido a que la fauna silvestre es un componente esencial en la epidemiología de muchas EIDs,

el estudio de patógenos en animales silvestres será esencial para identificar las causas y

desarrollar políticas y estrategias para mitigar estas amenazas.

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The 20th century has seen an advance in

human health without precedent in history.

Coupled with other improvements in food

intake and sanitation, the development of

vaccines and antibiotics contributed to the

steady enhancement in demography and

economic growth in many parts of the world

(WHO, 1999). Therefore, it became possible to

imagine a world without the burden of

pathogens and infectious diseases to humans.

However, this optimist was premature, and

drove to an erroneous policy by reducing

investment in infectious diseases research

(Berkelman et al., 1994). As a result, since

1940s millions of people have died because

more than 300 events of emerging and re-

emerging infectious diseases (EIDs) (Jones et

al., 2008). These EIDs are caused by

pathogens that have evolved resistance (multi-

drug resistance tuberculosis and chloroquine-

resistant malaria), pathogens from animals that

now infect humans (HIV-1), or pathogens that

have been probably presented in humans for

centuries but which have recently increased in

incidence and geographic range (for example,

Lyme disease). Ironically, the economic and

health successes of the last century also

contributed to the increase of these pathogenic

diseases, as “hidden costs” of this wellness.

For example, economic and demographic

growth led to urbanization, where millions of

people live in crowded conditions, thereby

facilitating the spread of infections (Neiderud,

2015). Moreover, with the aim to meet the

demands of the growing population, the

indiscriminate deforestation for logging and

farming in tropical rainforests have provoked

changes in the ecology and epidemiology of

vector-borne diseases (e.g. malaria,

leishmania and Chagas Disease), thus putting

vulnerable populations at risk for infection

(Sehgal, 2010). Furthermore, the current speed

and reach of travel of transport in our

globalized world promoted the fast spread of

Severe Acute Respiratory Syndrome (SARS)

from a single case, infecting over 8.000 people

in 26 countries across 5 continents in two

weeks (Peiris et al., 2004). Thus, it is clear that

EIDs represent a formidable threat to global

health.

There is one point in the EIDs that should be

highlighted, because sometimes is neglected:

the essential information provided by studies

on wildlife. Why are they so important? On one

side, more than 60% of these diseases in

humans are caused by pathogens spread from

animals. For example, pandemic strains of

influenza can emerge from avian and swine

reservoirs. Furthermore, 71.8% of these

zoonotic diseases events are provoked by

pathogens with a wildlife origin (Jones et al.,

2008). For instance, many experts believe that

HIV, the virus causing AIDS, evolved from a

virus carried by a nonhuman primate in West

Africa. Because wildlife is an essential

component in the epidemiology of many EIDs,

the study of pathogens in wildlife will be

essential to successfully develop policies and

strategies to mitigate these threats. On the

other side, another point highlighting wildlife

studies on EIDs relies on their trustworthy

conclusions on the ecological drivers of the

epidemiology. In this sense, confounding

factors may cause an incorrect analysis of

results and erroneous conclusions in the study

of EIDs. In humans, socio-cultural and

economic drivers (e.g. population density,

economic growth), as well as ecological and

environmental conditions (wildlife species

richness, rainfall) may be major determinants

of surge and spread of diseases. The formers

are restricted to human populations, but the

latter are shared with other animal species in

the human-wildlife ecosystem interface.

Therefore, the investigations of pathogen

diseases in wildlife allow us to eliminate

socioeconomics and cultural confounding

variables from the study, and hence to achieve

firm conclusions. Consequently, I call for an

increasing number of studies on parasitology

in wildlife as an important tool for

identification of potentially zoonotic

pathogens and hence reducing the likelihood

Marzal

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Neotropical Helminthology. Vol. 9, Nº2, jul-dec 2015 Emerging Infectious Diseases and Wildlife

of future zoonotic disease emergence.

Because their rapid increase, infections with

vector-borne pathogens have become one of

the main EIDs in the last decades. Mosquitoes,

bugs, ticks and many other arthropods are

responsible for transmission of viruses

(dengue, Chikungunya, West Nile virus),

protozoans (malaria, Chagas) and bacteria

(Lyme disease) infecting billions of people

every year. Anthropogenic global changes

(deforestation and land use change) have been

proposed to cause the expansion of mosquito

vector and the reemergence of malaria and

dengue in South America (Daszak et al., 2000).

But this issue requires further studies

removing potential confounding variables. As

has been mentioned before, the factors

favouring malaria outbreaks go beyond the

basic biological elements and include

ecological as well as socio-economic factors

(Wilson, 2001). But these confounding effects

are irrelevant in the context of parasites that

infect wild animals. Studies on malaria

parasites of birds have contributed

significantly to the knowledge on biology and

ecology of malaria parasites of other

vertebrates, including human malaria (Marzal,

2012). Nowadays, research on avian malaria

will be essential to fence these new health and

environmental challenges.

Additionally, the introduction of domestic

animals and wildlife alien species can also

provoke emerging diseases with tremendous

costs in terms of loss of biodiversity, mortality

and economic expenses. We have many

examples in which a foreign species can act as

a “Trojan horse” because they can bring exotic

parasites and pathogens inside them, and thus

allowing its dissemination in the new areas.

For example, Europeans introduced smallpox

and measles to the Americas with fatal

consequences for indigenous people. Also, a

highly pathogenic morbillivirus disease (The

African rinderpest panzootic) destroyed

populations of many species of both domestic

and wildlife ungulate species in seven years,

and contributed to the famine and death of

many livestock-depending African tribes

(Spinage, 2003). In addition, avian malaria

Plasmodium relictum Grassi & Feletti, 1891 is

a widely pathogenic species, being responsible

for mass mortality, population declines and

even extinctions of many bird species

worldwide after its introduction outside its

native range (Valkiūnas, 2005). Recently this

invasive malaria has been found infecting

birds from Peru (Marzal et al., 2015),

representing a potential threat to over one-third

of all bird species in the world. Therefore,

introduced species may bring new diseases

affecting biodiversity, ecosystem function and

global health.

Finally, I would like to emphasize one very

important issue. Most of surveillances and

infectious diseases researches have been done

in Europe, North America and Australia, which

is in sharp contrast with the predicted areas of

higher risk of zoonotic EIDs from wildlife in

tropical Africa, Latin America and Asia (Jones

et al., 2008). These dissimilarities seem not to

be very practical in the challenge of new EIDs,

with the majority of scientific resources

invested on areas where the next emerging

pathogen or the new disease outbreak is highly

unlikely to occur. I hence encourage for an

urgent need for surveillance and monitoring

studies on wildlife parasites as a potential

threat for EIDs in these high-risk places. I also

recommend promoting the creation of

international networks on the study of

emerging diseases as a valuable strategy for

preventing EIDs on the 21 century. Scientists

and experts from emerging disease hotspot

areas should play a key role in these networks.

It would enhance the collaboration,

communication and education among its

members, and provide a fast assistance during

outbreak investigations.

In conclusion, we all (humans, wildlife and

domestic animals) live in the same world,

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sharing many pathogens and diseases.

Deforestation, the introduction of pathogens

through invasive species and anthropogenic

land use change have increased the pathogen

transmission at the human-livestock–wildlife

interface, which have facilitated the spread of

new and re-emerging infectious diseases.

Despite significant attention given to these

diseases in the last half-century, our

understanding of EIDs epidemiology and how

to manage them remains limited. Studies on

parasites on wildlife would provide valuable

information to identify underlying causes and

to control their spread. In the fight against

these infections, the creation of international

networks with a multidisciplinary perspective

involving scientists, educators, policy makers

and practitioners would be desirable.

The author thanks Editorial Board from

Neotropical Helminthology for the invitation

to write this review. This study was funded by

research projects of the Spanish Ministry of

Economy and Competitiveness (CGL2012-

36665) and Junta de Extremadura (GRU:

15117).

Jones, KE, Patel, NG, Levy, MA, Storeygard, A,

Balk, D, Gittleman, JL & Daszak, P. 2008.

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diseases. Nature, vol. 451, pp. 990-993.

Marzal, A, Garcia-Longoria, L, Callirgos JM &

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as an emerging parasitic disease in native

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978-953-51-0326-4, DOI: 10.5772/33730.

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ACKNOWLEDGMENTS

Marzal

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Received December 15, 2015.

Accepted Accepted 22, 2015.