Unit 12: Diseases and Infections
B: Examine the transmission of infectious diseases and how this can be
prevented
The prevention of infectious diseases
This report will outline the causes and transmission of infectious diseases and the methods being
used to combat the spread of these diseases to inform the World Health Organisation’s publications,
newsletters and blogs.
Diseases that are spread through direct contact
Direct contact diseases are brought on by pathogens that are transferred from person to person or
through contact with infected materials [1]. These types of diseases tend to spread through the
following ways: from human to human through bodily fluids and from animal to human through
animal bites/waste.
Human to human transmission
Diseases involving direct contact between two individuals are transmitted when bodily fluids such as
blood, saliva, urine, faeces or sperm come into direct contact with an uninfected person via kissing,
sexual contact or a needlestick injury [2].
An example of a disease transmitted in this way is hepatitis B, which is caused by the Hepatitis B virus
(HBV) [2]. Hepatitis B is transmitted when an infected individual's blood, sperm or other bodily fluid
enters the body of an uninfected person [3]. This can happen through sexual contact, the sharing of
needles, syringes or other drug-injection equipment, or transfer from mother to baby at birth [3].
Getting vaccinated is the most effective strategy to avoid hepatitis B; the hepatitis B vaccination is
both safe and effective [4]. To be totally protected, you must obtain all doses in the vaccination
programme [4].
Animal to human transmission
Diseases can be spread from animals to humans when an individual comes into direct contact with
an infected animal's saliva, blood, urine, mucus, excrement, or other body fluids [5]. These types of
diseases are known as zoonotic diseases [5].
An example of a zoonotic disease is histoplasmosis [6], which is caused by the pathogen Histoplasma
[7]. The disease develops in a person if they inhale the fungus's spore stage [8]. Outbreaks may occur
in groups that have had similar exposures to bird or bat droppings or recently disturbed,
contaminated soil found in chicken coops [8]. Histoplasmosis does not spread from person to person,
making it a non-communicable disease [8].
To prevent the spread of histoplasmosis, one can reduce dust exposure in contaminated and
enclosed environments, such as chicken coops and surrounding soil [8]. Using a dust mask and
spraying the area with water may also help to reduce dust exposure [8].
,Unit 12: Diseases and Infections
B: Examine the transmission of infectious diseases and how this can be
prevented
Diseases that are spread through indirect contact
Indirect contact transmission involves the transfer of a pathogen through an infected object [9] or
when certain pathogens persist in the air for a long period of time and infect one's immune system
[10]. These types of diseases tend to spread through the following ways: vectors (mosquitos, fleas,
lice, ticks), infected surfaces, infected water droplets and contaminated food/water.
Vectors
Vectors can cause disease by ingesting pathogens and transmitting them to humans e.g. through
bites [11]. The disease replicates or develops in the vector, allowing it to spread by infecting an
animal or a human [11]. This process is known as biological transmission [11].
An example of disease caused by vectors is Chagas disease [12], which is caused by the pathogen
Trypanosoma cruzi [13]. Chagas disease spreads via the triatomine bug, blood/blood products,
mother-to-child transmission, organ transplantation and laboratory mistakes [14].
Chagas disease can be prevented by avoiding sleeping outside or in mud-brick houses [15]. If you
must sleep outside, use an insecticide-treated bed net [15]. Take precautions with food and water
and avoid receiving blood transfusions or organ transplants in areas where Chagas disease has been
identified [15].
Infected surfaces
An individual can be infected with a disease through infected surfaces when contaminated materials
or surfaces come into contact with the skin or mucous membrane [15].
An example of a disease caused by contact with infected surfaces is chickenpox [15], which is caused
by the Varicella-zoster virus (VZV) [16]. Chickenpox is spread from person to person by directly
contacting an infected individual's blisters, saliva, or mucus [17]. Coughing and sneezing can
potentially spread the infection through the air [17].
The best approach to avoid chickenpox is to be vaccinated [18]. Children, adolescents and adults
should receive two doses of chickenpox vaccine if they have never had chickenpox or were never
immunised [18]. Aside from immunisation, the spread of chickenpox can be avoided by practising
excellent hygiene and routinely washing your hands [19]. Reduce your contact with people who have
chickenpox [19]. Stay at home if you already have chickenpox until all of your blisters have dried and
crusted over [19].
Infected water droplets
Diseases that are spread through contact with infected water droplets are known as airborne
diseases. Airborne diseases can spread when people cough, sneeze or talk, releasing nasal and throat
secretions into the air [20]. Some viruses or bacteria fly through the air and land on other people or
surfaces [20].
,Unit 12: Diseases and Infections
B: Examine the transmission of infectious diseases and how this can be
prevented
An example of a disease caused by airborne transmission is measles [20], which is caused by the
pathogen Morbillivirus [21]. Measles can be spread by: contaminated droplets in the air caused by
coughing, sneezing or talking; kissing someone who has measles; sharing food or beverages with
someone who has measles; shaking/holding hands with someone who has measles; hugging
someone who has measles; or pregnant women transferring it to their babies (during pregnancy,
delivery, or while nursing) [22]. Even after the individual with measles has left the room, the airborne
respiratory droplets might linger [22]. It might take 6 to 21 days following infection to develop
symptoms of measles [22] (known as the incubation period) [22]. The infected individual becomes
contagious for four days before the rash appears and four days after the rash appears [22].
There are two kinds of measles vaccinations; the MMR (measles, mumps, rubella) vaccination and
the MMRV (measles, mumps, rubella, varicella) vaccine [22]. The MMR vaccination is frequently
administered in two doses [22]. The first dose is given between the ages of 12 and 15 months- the
second dose is given around the age of 4 or 5 years [22]. Measles can still be avoided in children who
have not been immunised by obtaining the vaccination within three days of being exposed to the
virus [22]. The MMRV vaccination is only offered to children between the ages of 12 months and 12
years [22]. Between the ages of 12 and 15 months, the child should receive one vaccination [22]. The
child should have the second shot between the ages of 4 and 6 [22]. The second injection, however,
can be administered three months following the first [22]. When in contact with bodily fluids,
employees at a healthcare facility should wear personal protection equipment such as masks, gowns,
and clothing [20]. Hands should be cleaned before and after putting on gloves [22]. Individuals who
work with children or in other sectors are advised to avoid direct contact with people who are ill and
to wash their hands properly [22].
Contaminated food/water
Diseases that are caused by contaminated food and water are the result of the transfer of
microorganisms by the faecal-oral route (consumption of faeces-contaminated food and drinks) [23].
An example of a disease caused by contaminated food or water is Hepatitis A [24], which is caused by
the Hepatitis A virus (HAV) [25]. The hepatitis A virus is typically spread by the faecal-oral route,
which occurs when an uninfected individual consumes food or drink contaminated with the
excrement of an infected person [26]. This may occur in households when an infected individual
prepares food for family members [26]. The virus can also be transferred by close physical contact
(such as oral-anal sex) with an infected individual, however casual contact between individuals does
not lead to transmission of the disease [26].
People with hepatitis A are advised not to prepare food or care for the elderly or small children for at
least two weeks after the onset of symptoms [27]. HAV can be eliminated by boiling or heating meals
for at least 1 minute at 85°C [27]. Foods and drinks prepared to this temperature and for this period
of time do not spread HAV infection unless they become contaminated after heating [27]. Travellers
can reduce their risk of hepatitis A and other food-borne illnesses in developing countries by drinking
only boiled or chemically purified water, eating only properly heated foods and avoiding fruits and
vegetables that have not been peeled or prepared by the traveller personally [27].
, Unit 12: Diseases and Infections
B: Examine the transmission of infectious diseases and how this can be
prevented
Methods to prevent diseases
Diseases can be prevented through the following methods: vaccination, prophylaxis (antimalarial,
antibiotics and antiviral), PPE (face masks, gloves, biohazard suits), the use of mosquito nets,
practising safe sexual intercourse, implementing good hand washing practice, the use of chemical
sprays (pesticides), no open clean water sources and isolation/quarantine.
Vaccination
Vaccination programmes involve giving vaccinations to people of a certain age to protect them from
certain diseases [28]. An example of a vaccination programme is the MenACWY vaccination [29]. The
MenACWY vaccination is administered via a single injection into the upper arm and protects against
four types of meningococcal bacteria that cause meningitis and blood poisoning: A, C, W and Y [2].
Children aged 13 to 15 are typically provided the MenACWY vaccination in school, along with the
3-in-1 teenage booster [29].
Evaluating different types of vaccines
Modified live attenuated vaccines
Modified live attenuated vaccinations use a weakened form of the pathogen which triggers a disease
[30]. They are used to protect against the following diseases: measles, mumps, rubella, rotavirus,
smallpox, chickenpox and yellow fever [30]. These vaccines produce a powerful and long-lasting
immune response because they are so identical to the natural infection that they help avoid [30].
Most live vaccines require only one or two doses to provide lifetime protection against a pathogen
and the disease it causes [30].
Modified life attenuated vaccines are well-established technology and they can provide a strong
immune response with the help of B cells and T cells [31]. They are also relatively simple to
manufacture [31]. However, they can be unsuitable for people with compromised immune systems
and in very rare cases, they may trigger disease [31]
They are temperature sensitive so careful storage of them is necessary [31].
Inactivated vaccines
Inactivated vaccinations make use of the killed version of a pathogen that causes a disease [30]. They
often do not provide as strong immunity (protection) as live vaccines, so an individual may require
several doses over time (booster injections) to maintain continuous immunity against illnesses [30].
Inactivated vaccinations are used to protect against hepatitis A, influenza (by shot only), polio (by
shot only) and rabies [30].
Inactivated vaccinations can lower the risk of death in kidney transplant recipients [32]. Inactivated
vaccines can provide a high level of disease protection if the dose and booster regimen is followed
[33]. Top-up doses are required, although if they are given as directed, the protection provided by
inactivated vaccines is of very high value [33]. Inactivated vaccinations are particularly beneficial
