10.3.3. Biological
agents
Acronyms
10.3.3.1.
Introduction
Biological hazards include viruses, bacteria and fungi and
more recently discovered agents such as prions; often, they are ubiquitous and
can all pose serious risks to public health, particularly in combination with
the growing impact of antimicrobial resistance. Biological stressors are
responsible for the occurrence of a variety of communicable diseases. Of the 49
diseases under surveillance by the European Centre for Diseases Control (ECDC),
21 have incidence levels that are in double or triple digits per million
population with half of these 21 also having rising (or steady) trends. The
fact that three of the six communicable diseases with the highest incidence in
the EU belong to this group, and include the two diseases with the highest
crude incidence rates in the EU (Chlamydia infection and Campylobacteriosis)
which could in part be due to improved surveillance represents a great concern.
In 22 diseases, the age groups most affected were under 24 years of age,
indicating that more action is needed to protect the health of our future
generations. Of the main disease groups, the ‘Zoonoses’ and ‘Serious imported
disease’ groups had the lowest incidence rates and also show decreasing trends
(except for avian influenza and malaria). Every year approximately three
million people in the European Union catch a healthcare-associated infection
and approximately 50 000 of these people die as a consequence. The most
important communicable disease threat in Europe is posed by the increasing
number of micro-organisms strains that have become resistant to antibiotics.
10.3.3.2. Data
sources
See Chapter 6.
10.3.3.3. Data
presentation and analysis
Antimicrobial resistance (AMR)
The bacterium that has received prime attention is methicillin-resistant
Staphylococcus
aureus
(MRSA). A larger and larger proportion of all invasive S. aureus
infections is caused by MRSA. Evidence from the countries participating in the
EU-funded EARSS surveillance program, including countries with high, medium and
low baseline figures, shows that a general increase in MRSA is occurring
throughout Europe (Figure 10.3.3.1). However, two countries (Slovenia and
France) have succeeded at significantly reducing the proportion of MRSA, thus
demonstrating that this MRSA pandemic may not be irreversible.
Figure
10.3.3.1. Proportion of
MRSA isolates in 2005 in Countries participating to EARSS project
For most other bacteria under EU surveillance the overall
trend is also very worrying, with AMR is a particular concern when it comes to
the global killer diseases TB, malaria, HIV and pneumococcal infections.
Resistance has also evolved against viral (e.g. HIV, influenza), parasitic
(malaria) and fungal infections, making AMR the most serious of all threats associated
with communicable disease.
Viruses
Viruses are among the most dangerous biological agents for
human health. Seasonal influenza is an acute viral disease of the respiratory
tract, caused by influenza virus A and B; each year there are epidemics during
the winter season, although sporadic cases do occur throughout the year;
seasonal influenza poses a considerable public health threat. SARS is a viral
respiratory illness with a high fatality rate, caused by a corona virus, the
SARS-associated corona virus (SARS-CoV); the main way that SARS seems to spread
is by close person-to-person contact, through respiratory droplets produced
when an infected person coughs or sneezes. Human immunodeficiency virus (HIV)
is a retrovirus, which attacks the immune system and may
lead to severe illness following a long incubation period. The end-stage of the
infection, acquired immunodeficiency syndrome (AIDS), results from the
destruction of the immune system. Measles is an acute illness
causes by morbillivirus. Mumps is caused by the mumps virus. Rubella is a mild
febrile rash illness affecting both adults and children. The most serious
consequence of rubella results from infection during the first trimester of
pregnancy, when rubella infection can cause miscarriage, foetal death or severe
birth defects. Polio is caused by poliovirus, which infects the
gastrointestinal tract and spreads to regional lymph nodes, but can also spread
to the central nervous system. In recent years, a new strain of avian influenza
(A/H5N1) has spread globally among birds, and also occasionally infected
humans. The threat of avian influenza and its potential for starting a human
influenza pandemic is a main concern. Hepatitis A is declining in Europe, but this also means that more and more people remain susceptible to this virus and
smaller outbreaks are still seen in several countries. An effective vaccine is
available but it is recommended mostly for travellers. Norovirus and rotavirus
infections are not reportable in the EU, but are both important causes of
gastroenteritis all over the Union. It may be that outbreaks caused by
norovirus in confined places, such as schools, hospitals and cruise ships are
on the increase, but it should be noted that methods for laboratory diagnosis
have really been available only in the last decade.
Bacteria
Bacteria may also have very dangerous biological
stressors. Tubercolosis is a bacterial disease, which affects the lungs as well
as many other organs; it is most commonly acquired via inhalation of bacteria
belonging to the Mycobacterium tuberculosis complex in droplets produced
by another person with pulmonary disease, and less frequently through ingestion
of contaminated milk or through laboratory contamination. Legionnaires’ disease
is a respiratory disease caused by the bacteria Legionella pneumophila,
which can give severe pneumonia with high case fatality rates, especially among
elderly and immuno-compromised individuals. Streptococcus pneumoniae
(pneumococcus) mainly affects the youngest and oldest individuals, and is the
main cause of bacterial respiratory tract infections in all age groups.
Invasive meningococcal disease, caused by the bacterium Neisseria
meningitides (meningococcus), is most common in young children, with a
secondary peak in disease incidence among teenagers. Haemophilus influenzae
type b (Hib) is a respiratory tract bacterium, capable of causing meningitis
and other severe systemic infections in young children. Pertussis is an acute
bacterial infection of the respiratory tract caused by the Bordetella
pertussis bacterium. The disease is characterised by an irritating cough
that may last up to two months or even longer. Diphtheria is an acute disease
with inflammation of the mucosal surfaces of the upper respiratory tract caused
by a toxin from the Corynebacterium diphtheriae bacterium. Tetanus is
induced by an exotoxin of the Clostridium tetani bacterium. Two
important food-born or water-borne infections, salmonellosis (including typhi
and paratyphi) and shigellosis, seems to be on a declining trend in the EU. Campylobacter
is the most commonly diagnosed food-borne bacteria in the EU, and may be
slightly increasing over time, while Cryptosporidium has caused
waterborne outbreaks in several Member States. Although the majority of the
symptomatic Campylobacter and Salmonella infections do not
require any drug treatment, invasive infections do occur. Zoonoses are diseases
or infections, which are transmissible from animals to humans. The infection
can be acquired directly from animals or through the ingestion of contaminated
foodstuff. In humans, the gravity of these diseases can vary from mild symptoms
to life threatening conditions. The importance of a zoonosis as a human disease
depends on several factors, such as the severity of the disease, the case
fatality and number of cases (incidence) in the population.
Parasites
Parasites are other well known biological stressors. Toxoplasmosis
is caused by the protozoan parasite Toxoplasma gondii. The infection is
asymptomatic in most humans, but can be life-threatening in immuno-compromised
individuals. Giardiasis is a parasitic infection caused by Giardia
intestinalis, causing both acute and chronic diarrhoea. Infants and
children are at particular risk. Cryptosporidiosis is a parasitic disease
caused by Cryptosporidium, infecting many species of large and small
animals. The parasite can cause profuse and watery diarrhoea; humans can be
infected from other people or from the environment. Echinococcosis is a
zoonotic parasitic disease, caused by the larval stage of the tapeworm Echinococcus.
Humans are infected through close contact with infected animals (sheep, cattle,
goats, horses, pigs) or through ingestion of undercooked infected food.
Trichinellosis is a zoonotic disease caused by Trichinella. The first
symptoms are diarrhoea and abdominal cramps, but following larval invasion to
the muscles, muscular pain and fever become characteristic symptoms.
Prions
Variant Creutzfeldt-Jakob disease (vCJD) is a novel form
of human spongiform encephalopathy (prion disease). The clinical picture is
characterised by psychiatric symptoms followed by progressive neurological
deterioration. The disease is fatal, with a mean survival of about 14 months.
The main suspected route of transmission is through past consumption of
infected beef products, although recently human-to-human transmission has been
described through blood transfusion. Preventive measures include ensuring that
the BSE prions, mainly localized in the brain and other parts of the nervous
system of infected cattle, do not enter the human or animal food chains, and
that blood or tissue for transplants from potentially infected persons are not
used in medical care.
BSE prion was found to be highly resistant to thermal
inactivation and to digestion in the gastro-enteric tract.
Impact on health of specific biological hazards
For some diseases there has been a significant reduction
in the incidence and number of cases through concerted prevention and control action
by Member States (even though levels remain high in specific population
segments and risk groups) (table 10.3.3.1).
Table 10.3.3.1.
Summary of general trends (1995–2005), main age groups affected (2005), and major
threats detected (2005) for diseases reported on EU-level
10.3.3.4. Control
tools and policies
See Chapter 6.
10.3.3.5. Future
developments
See Chapter 6.
10.3.3.6.
References
See Chapter 6.
