Infectious and non-infectious Diseases
Germs (including bacteria, viruses, and fungi) that enter the body, grow and have the
potential to cause an infection are the source of infectious diseases. Certain infectious
diseases have the potential to spread from person to person and are therefore considered
communicable (when an infection/disease is contagious). 1
Chronic diseases, commonly known as non-communicable diseases (NCDs), are
characterised by an extended duration and a combination of behavioural, physiological,
environmental, and genetic factors. Diabetes, malignancies, chronic respiratory conditions
including asthma and chronic obstructive pulmonary disease, and cardiovascular disorders
like heart attacks and strokes are the primary categories of non-communicable diseases
(NCDs).2
Causes of non-infectious disease in humans
The use of tobacco products, physical activity, excessive alcohol consumption, poor diets,
and air pollution are the five main risks factors for NCDs. The NCD epidemic threatens to
bankrupt health systems and has terrible health effects on people, families and
communities.3
Non-infectious diseases can be generally classified as either genetic, dietary, degenerative,
and environmental.
Genetic
A genetic disorder is a condition where the normal DNA sequence is altered, either
completely or partially. Genetic disorders can result from damage to chromosomes, which
are structures that carry genes, or from mutations in one or more genes (monogenic
disorder), multiple genes (multifactorial inheritance disorder), or a combination of gene
mutations and environmental factors.4
Tay-Sachs Disease
The nervous system is impacted by a hereditary disorder called Tay-Sachs disease (TSD).
Over time, it gets worse and worse. When symptoms start to show up in previously healthy
kids, they usually do so around six months of age. Children with TSD often live to be five
years old.5
Symptoms of Tay-Sachs include:6
1
WHO WE ARE, https://www.cdc.gov/ncezid/who-we-are/index.html#:~:text=Infectious%20diseases%20are%20illnesses%20caused,from
%20one%20person%20to%20another., 25/04/2024
2
NONCOMMUNICABLE DISEASES, https://www.who.int/news-room/fact-sheets/detail/noncommunicable-diseases, 25/04/2024
3
NONCOMMUNICABLE DISEASES, https://www.who.int/health-topics/noncommunicable-diseases#tab=tab_1, 25/04/2024
4
GENETIC DISORDERS, https://www.genome.gov/For-Patients-and-Families/Genetic-Disorders#:~:text=Overview,away%20from%20the
%20normal%20sequence., 03/05/2024
5
TAY-SACHS DISEASE, https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/tay-sachs-disease, 06/05/2024
6
TAY-SACHS DISEASE, https://www.nhs.uk/conditions/tay-sachs-disease/#:~:text=Tay%2DSachs%20disease%20is%20a,people%20from
%20other%20ethnic%20backgrounds., 06/05/2024
, Muscle stiffness
Seizures (fits)
Loss of vision or hearing
Difficulty swallowing
Floppiness and weakness, which keeps getting worse until they’re unable to move
(paralysis)
Being very slow to reach milestones like learning to crawl, and losing skills they have
already learnt
Being overly stimulate with noises and movement
A genetic defect that causes a child’s nerves to malfunction is the cause of Tay-Sachs
disease. Only when both parents carry this defective gene can a child be affected. Being a
“carrier” is when one or both of the parents do not exhibit any symptoms.
Based on the Punnett square diagram below, we can see that a child of two carriers has a 1-
in-4 chance of being a non-carrier and a 1-in-4 risk of having the disease. The child also has a
2-in-4 probability of becoming a carrier without having the disease. 7
Cystic Fibrosis
The genetic condition known as cystic fibrosis is characterised by an accumulation of viscous
mucus that can harm numerous organs in the body. The respiratory system’s gradual
deterioration and persistent digestive system issues are the disorder’s most prevalent signs
7
HOW DOES THE PUNNETT SQUARE HELP DETERMINE TAY-SACHS DISEASE?, https://www.quora.com/How-does-the-Punnett-Square-
help-determine-Tay-Sachs-disease#:~:text=As%20this%20Punnet%20square%20shows,%2C%20in%20the%20lower%2Dright., 06/05/2024
, and symptoms. The disorder’s characteristics and severity differ among those who are
impacted.8
Symptoms of cystic fibrosis include:9
Frequent lung infections (recurrent pneumonia or bronchitis)
Loose or oily stool
Trouble breathing
Frequent wheezing
Frequent sinus infections
A nagging cough
Slow growth
Failure to thrive (inability to gain weight despite having a good appetite and taking in
enough calories)
The primary cause of cystic fibrosis is alterations to the transmembrane conductance
regulator, or CFTR. On a cell’s surface, CFTR produces a protein that functions as an ion
channel. Ion channels are similar to gates that let specific chemicals through the membrane
of a cell. For chloride ions, a class of mineral with a negative electrical charge, CFTR typically
creates a gate. Mucus becomes thinner and slicker as chloride exits the cell and takes water
with it. This is prevented in cystic fibrosis (CF) patients by gene mutations in the CFTR, which
keeps the mucus thick and sticky.
Based on the Punnett square diagram below, we can see that a child of two carriers has a 1-
in-4 chance of being a non-carrier and a 1-in-4 risk of having the disease. The child also has a
2-in-4 probability of becoming a carrier without contracting cystic fibrosis.
10
F f
F FF Ff
f Ff ff
Ff = mother
Ff = father
f = cystic fibrosis allele
Dietary
Nutrition disorders are illnesses that develop when a person’s diet is inadequate in nutrients
for optimal health or when their body is unable to properly absorb nutrients from meals.
Undernutrition, overnutrition, or an improper nutrient balance can all lead to nutrition
diseases.11
8
CYSTIC FIBROSIS, https://medlineplus.gov/genetics/condition/cystic-fibrosis/, 06/05/2024
9
CYSTIC FIBROSIS, https://my.clevelandclinic.org/health/diseases/9358-cystic-fibrosis#symptoms-and-causes, 06/05/2024
10
GENETIC TESTING AND CYSTIC FIBROSIS, https://www.bbc.co.uk/bitesize/guides/z8nqcj6/revision/2, 06/05/2024
11
NUTRITION DISORDERS ARTICLES FROM ACROSS NATURE PORTFOLIO, https://www.nature.com/subjects/nutrition-
disorders#:~:text=Nutrition%20disorders%20are%20diseases%20that,an%20incorrect%20balance%20of%20nutrients., 03/05/2024