DISEASE EPIDEMIOLOGY: DISEASE OUTBREAK MODELLING.

DISEASE EPIDEMIOLOGY: DISEASE OUTBREAK MODELLING
DISEASE EPIDEMIOLOGY: DISEASE OUTBREAK MODELLING
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DISEASE EPIDEMIOLOGY: DISEASE OUTBREAK MODELLING1
Introduction
Epidemiology is the study dealing with understanding the dynamics of disease outbreak
and transmission so as to facilitate the development of preventive mechanisms for the same.
Despite the prevalence of extensive medical advancements as well as vaccines, it is worthwhile
to remember that disease outbreaks and epidemics yield considerable financial losses and
casualties across the world and are often too complex in nature so as to be prevented by merely
treatment or vaccination alone. Thus, to ensure timely detection and prediction of a disease
outbreak, engaging in an epidemiological formula may prove to be beneficial and cost effective
(Ramos da Silva & Gao, 2016).
The following paper thus aims to discuss on predictive models of infectious diseases and
disease outbreaks which can then be used to predict and prevent future incidences and associated
mortalities. The disease which will be chosen for the same is West Nile Fever (WNF) caused by
the West Nile Virus (WNV). To explain the same, a susceptible, exposed and recovered (SIR)
model coupled with a no-linear, differential equation will be considered. For the purpose of
predicting a future predictions in case of successful interventions, an exponential based
epidemiology equation will be used, with the help of a compartmental Susceptible, Exposed,
Infectious and Susceptible (SEIS) model.
Discussion
Disease Characteristics
Disease History
The West Nile Virus (WNV) is the key causative factor for the West Nile Fever (WNF) –
an infectious disease with debilitating neurological symptoms. This infectious disease has been

DISEASE EPIDEMIOLOGY: DISEASE OUTBREAK MODELLING2
found prevalently across populations residing in countries like Europe, Africa, North America,
the Middle East and the Western part of Asia. The virus undergoes vector-borne transmission,
that is, via mosquito bites. The WNV belongs to viruses of the genus ‘Flavivirus’ which is a part
of the antigenic and Japanese encephalitis complex known as the ‘Flaviviridae’ family. The key
hosts responsible for the transmission of WNV are birds, which is why, the cycle of WNV
disease transmission and outbreak is limited to ‘birds-mosquitoes-birds’ (Tisoncik-Go & Gale Jr,
2019).
It has been evidenced that disease outbreaks by the WNV first originated in Africa, where
the virus was isolated first from a woman was residing in the Ugandan district of West Nile, in
the year 1937. In the year 1953, the virus was found to be prevalent in birds like crows which
were residing in the delta region of West Nile (Parkash et al., 2019). Since the last 5 decades, the
prevalence rate of incidences of infections caused by WNV have increased extensively, most
notably in the United States during early 21st century which was in turn attributed to have been
imported from disease incidences reported in African and Middle East regions like Tunisia and
Israel. The high incident rate of WNV in the United States reported in the decade ranging from
1999 to 2000 demonstrated the highly infectious, transmissible and fatal nature of this condition,
which in turn, paved the way for development of epidemiological and disease based modelling
and preventive strategies (Williamson et al., 2017).
Disease Progression
The transmission and progression of infection by WNV across humans is facilitated
largely via mosquitoes which have been infected and are carriers of the same (Sinigaglia et al.,
2019). The World Health Organization (WHO, 2017) also denoted the positive associated
between high rates of WNV infection transmission and the summer and monsoon season or

DISEASE EPIDEMIOLOGY: DISEASE OUTBREAK MODELLING3
during temperature climatic condition found prevalently between the months of July and October
in Europe and the United States. WNV infects mosquitoes after the latter feeds on infected birds.
After the viral strain transferred to the salivary glands of the vector, it is likely that the mosquito
injects the same into other organisms and humans after feeding on blood from the latter.
Ironically, the infection has been found to be asymptomatic in approximately 80% of those who
have been infected (Sinigaglia et al., 2019). The remaining approximate 20 to 30% are likely to
be infected West Nile Fever – an infections with symptoms like body aches and head aches,
persistent fever, vomiting, nausea, rash and an inflamed lymphatic system (WHO, 2017). The
predicted incubated period for the above symptoms to appear is 3 days to 14 days. However, it
has been estimated that approximately one out of 150 infections are at risk of acquiring a neuro-
invasive form of WNV infection, known as West Nile meningitis or encephalitis or
poliomyelitis, and is characterized by fatal neurological symptoms like convulsions, tremors,
stupor, muscular pain and weakness, coma, disorientation, persistent high fever and headaches
and fatigue. The risk of acquiring such symptoms, though rare, are higher in case of older
individuals aged 50 years or above and those whose immunological status is likely to be
compromised, that is patients undergoing organ transplantation (Ronca, Murray & Nolan, 2019).
Disease Containment
According to the Centers for Disease Control and Prevention (CDC, 2019), fever due to
WNV is caused in individuals who have been bitten by mosquitos infected with the same. It has
been estimated that the virus is likely to cause fever and the above identified symptoms across
one out of a total of five individuals who may be bitten by a mosquito infected by WNV.
Additionally, it has been estimated that the WNV may also cause fatal neurological symptoms
and possibly death in one out of a total of 150 individuals bitten by an infected mosquito. No