These are the most frequently used words in this book.
ability
acid
act
against
although
animals
antibiotics
antibodies
antigen
areas
bacteria
bacterial
blood
body
cannot
cause
causing
cells
certain
countries
defences
develop
different
disease
during
environment
even
factors
flora
food
form
function
fungal
fungi
health
hepatitis
host
however
human
immune
immunity
individual
infect
infected
infection
infectious
intestinal
known
large
life
live
liver
macrophages
man
may
microbes
microorganisms
normal
number
occur
once
organisms
parasites
part
particular
pathogens
people
population
process
produce
proteins
regards
result
risk
see
sex
sexual
since
skin
small
species
specific
spread
still
substances
symptoms
system
time
tissue
transmitted
types
use
usually
vaccine
various
viral
virus
viruses
water
world