**2.1 Lower respiratory tract infection epidemiology**

As per World Health Organization lower respiratory tract infections are caused mainly by influenza, pneumococcal pneumonia and viral pneumonia are responsible for 3 million deaths [11]. The WHO reported in 2018, 3–5 million cases of Influenza with 290,000–650,000 death cases annually [12]. As per the Global Disease burden (GDB) study report of 2015 there were around 1.5 million deaths in all age groups caused due to pneumococcal pneumonia [13]. SARS (Corona virus) causes viral pneumonia; it is epidemic to more than 30 countries with 8000 reported cases and 774 deaths during the year 2002–2003. MERS is a viral pneumonia causing infections in 688 persons and 282 deaths reported by WHO in 20 countries during 2012 [14].

## **2.2 Influenza**

*Animal Models in Medicine and Biology*

**1.2 Pandemic disease**

time span [4].

**1.3 Vaccination**

during an epidemic outbreak [8].

**1.5 Fruit fly as a model organism for drug screening**

drug candidate were not well reviewed.

**1.4 Global requirement**

designated as an outbreak of a disease [1].

human population till the end of eighteenth century [3].

disease in a population within a fixed period could be considered as an epidemic disease. A disease lower than this fold increase, observed in a population could be

Diseases like tuberculosis, hepatitis, yellow fever, chikungunya, ebola virus disease, marburg virus disease, Crimean-Congo haemorrhagic fever, rift valley fever, typhoid fever, Shigellosis, plague, lassa fever, West Nile fever, zika virus disease, meningitis, MERS-CoV, plague, monkeypox, nodding syndrome, nipah virus infection are considered as epidemic diseases as per World Health Organization [2]. Epidemic diseases like plague, small pox and cholera caused unsurpassed deaths in

The term pandemic is derived from Greek word "pan" meaning "all" and "demos" meaning "people". It refers to an epidemic disease which spreads among large population possibly across geographic locations or continents within a short

Influenza, along with viral pneumonia, HIV and cholera are considered as pandemic disease and caused millions to die beside high rate of hospitalization and life threatening conditions across the globe [2]. The viral diseases like Influenza,

Vaccines are available for most of the epidemic and pandemic diseases [5]. Vaccination is the most effective prevention technique to suppress the infection in healthy population [6]. However, poor and conflicted regions of Asia and Africa are deprived of these vaccines [7]. World Health Organization plays a major role in epidemic preparedness in these regions and provides extended healthcare facilities

Considering, the disease outbreak and its transmission is high in a poor population of developing region [9]. First line and second line antibiotics are the most effective medicines for infected subjects as the vaccines are ineffective after the infection had taken place. First line therapy includes antibiotics are the most commonly prescribed medicines to alleviate the infection process, often not responsive on several types of multi drug resistant infection [10]. Hence it is important to select a cost effective model to screen the first line antibiotics or

Today, we need to discover more efficacious antibiotics to fight the infectious diseases. *Drosophila melanogaster* could be a useful model organism to study the infection process and to screen an efficient drug. Due to its shorter lifespan and vast genetic similarity towards vertebrates allows conducting the drug screening experiments. It is reviewed here that *Drosophila melanogaster* was already been used to study infections caused by pandemic and epidemic diseases. But how to utilize the fruit flies to study different infectious disease and techniques to screen a potential

cholera and HIV caused maximum deaths in the twenty-first century [3].

**108**

antivirals.

Influenza originates from *Orthomyxoviridae* family it can be differentiated into three types Influenza pandemic caused by Influenza A/B virus, seasonal Influenza and avian influenza (H5N1) [15]. Influenza virus causes upper respiratory tract infection often found to cause lower respiratory tract infection in association with bacterial co-invasion. The seasonal influenza leads to maximum hospitalization resulting fatality in infants during the seasonal outbreak [16].

#### **2.3 Pneumonia and viral pneumonia**

Pneumonia is caused due to several communicable infections usually known as community acquired pneumonia (CAP), often seen in hospitalized patients. Pneumonia can be caused by bacteria like *Streptococcus pneumoniae, Haemophilus influenzae type b (Hib),* and *Chlamydia pneumoniae, Staphylococcus aureus*, *Klebsiella pneumonia* and *Mycoplasma pneumonia.* Viruses like syncytial virus, adenovirus, rhinovirus, metapneumovirus, Influenza A/B viruses, Coronaviruses, parainfluenza virus including MERS and SARS causes viral pneumonia [17]. The viral pneumonia is the influenza often associated with bacterial infection thereby causing fatality better known as superinfection [18].

#### **2.4 Tuberculosis**

Tuberculosis is caused by *Mycobacterium tuberculosis*, a gram negative facultative anaerobic bacteria. In 2017 around 10 million people were infected with tuberculosis causing mycobacterium killing 1.6 million peoples across the world [19]. The current estimate of tuberculosis is not significantly different from the 2015 WHO report [20].

#### **2.5 HIV**

Currently HIV is the most fatal disease observed in human population across the globe. It caused maximum number of deaths around the world in the last 3 decades. As per the latest WHO report of 2019, HIV/AIDS have claimed more than 35 million deaths till date. Currently 36.9 million (31.1–43.9 million) peoples are living with HIV as of 2017 [21]. Although the rate of infection has decreased in the recent years, still HIV remains a global burden on world economy.

## **2.6 Diarrhoeal disease**

### *2.6.1 Cholera*

The term "cholera" was derived from Sanskrit meaning "stomach disturbance" [22]. Since, early 1800 century cholera outbreak turned out to be pandemic and caused millions to die, altogether six different pandemics took place the seventh started in the year 1961 and is still ongoing [23, 24]. In 2019 WHO report suggests 1.3 million to 4.0 million cases of cholera with an estimated 21,000–143,000 deaths worldwide [25].

#### **2.7 Hepatitis**

Viral hepatitis is one of the most life threatening disease, it causes death to 1.4 million peoples across the globe reported in 2018 [26]. Globally around 260 million peoples are infected with HBV and 71 million with HCV infections are reported causing 90% of deaths among viral hepatitis patients [27]. The HBV and HCV has the highest prevalence rate in the global population at present, hepatitis viruses like HAV, HAD and HEV are endemic in many countries [26]. Currently there is no vaccine available for HCV till date.

## **2.8 Typhoid**

The term Typhoid was coined from the Greek word "typhus" which means "Smoky" was used to relate the delirium symptom often associated with typhoid fever [28]. Typhoid fever is caused by gram-negative bacteria known as *Salmonella enterica serovar typhi*. Around 11–21 million cases of typhoid fever outbreak are reported annually, among that it causes death of 128,000–161,000 individuals worldwide [29].

#### **2.9 Malaria**

Malaria fever is a severe parasitic disease caused by *Plasmodium falciparum* and *Plasmodium vivax transmits through* female *Anopheles gambiae* mosquitoes. In the year 2017 219 million cases were noted by World Health Organization, this seasonal outbreak of malaria in 87 countries led to 435,000 deaths [30].

#### **2.10 Viral meningitis, viral encephalitis and hemorrhagic fever viruses**

Viruses like herpes simplex virus HSV, HIV, mumps virus, measles virus and west Nile virus causes meningitis which causes frequent outbreaks in some regions [31]. Japanese encephalitis virus along with genus *Alphavirus* Togaviridae family viruses are arbovirus (arthropod borne virus) like California encephalitis, Chikungunya, dengue, Eastern equine encephalitis, Powassan, St. Louis encephalitis, Sindbis virus, West Nile, Yellow Fever and Zika virus are capable of causing encephalitis in humans [32, 33]. The viruses capable of causing hemorrhagic fever are dengue virus, rift valley virus, yellow virus, Crimean-Congo Hemorrhagic Fever, Lassa virus, Marburg virus and Ebola virus are epidemic diseases [34].
