**6. Behavioral and physiological characterization of infected flies**

#### **6.1 Negative geotaxis assay**

Negative geotaxis assay serves the purpose to manifest ongoing pathogenesis inside the live model. It was demonstrated previously that infected flies display significantly lesser motility than healthy flies when exposed under bright light. It could be considered as an important parameter to explain drug efficacy while screening anti-microbial drugs in flies [59].

#### **6.2 Circadian rhythm**

Circadian rhythm in flies was studied, the genes timeless or period controls the circadian rhythm of activity-sleep cycle during day-night respectively. It has been observed that infected flies exhibit interrupted circadian control of locomotion thus flies with this deficit shows restlessness at the same time gets lesser sleep than normal flies. The behavioral changes could also be studied in infected flies beside the control/uninfected flies [60].

#### **6.3 Wasting**

Wasting is commonly seen physiological changes associated with prolonged diseased condition in humans. Wasting is a common symptom in HIV/AIDS,

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Drosophila melanogaster: *A Robust Tool to Study Candidate Drug against Epidemic…*

tuberculosis and cholera patients. Similarly rapid loss in weight could be seen in

It was previously reported that in order to replicate the outcome of future studies it is important to optimize the lethal dosage selection and the route of inoculum [63]. It is suggested that the selection of microbial strain and gender of flies are two important factors which could potentially impact the findings of future research.

There are two prime techniques for inducing infection in flies, primarily by feeding the flies with the microbes secondly by pricking micro needles dipped in bacterial liquid (inoculum) into fly's abdomen or thorax [62, 63]. Flies could be pricked in the abdomen with micro-needle dipped in the microbial solution, known amount can be useful in pharmacodynamic as well as pharmacokinetic studies [64].

Selecting gender should be considered strictly, few studies do not prefer to report the reason behind choosing the gender male/female type. In a study with *Vibrio cholera* infection narrated that female flies survived approximately 24 h

The existing models using live bacterial infusion, feeding fungal strains and transgenic flies expressing viral proteins. Under immuno-suppressed condition would serve multiple purposes like studying host pathogen interaction and con-

Since human viruses do not usually invade insects the use of *Drosophila melanogaster* as a model organism is critical and currently in less usage [67]. In order to establish an HIV model for drug screening in *Drosophila melanogaster* it is important to understand the structural components of human immunodeficiency virus (HIV). The envelope components are comprised of Gp120 and Gp41 encoded by *env* sequence, pol-Gag RNA material encodes for *Matrix, capcid, nuclear capsid, p6, Protease, reverse transcriptase, and Integrase), Vif, Vpr, Nef, vpu, tat,* and *Rev* [68]. Transfection of Tat (transcription activator), Vpu (helps virion budding), Nef (regulator of structural gene expression) and Rev. (Nuclear export protein) in flies (in-vitro/in-vivo) were previously shown, these transfection models could be useful due to the fact that there is no marketed drug to target these viral proteins [69]. The incapacity of Drosophila S2 cells is only associated with the expression of HIV-1 envelope proteins. It is possible to express gycosylated and cleaved Gp120 in S2 cells but fusion with CD4+ receptors of T-helper cells could not be achieved in the model expression system [70]. In another study the expression of Gp120 in drosophila was carried out in S2 cell line, the antigen Gp-120 did not exhibited T-helper cell mediated humoral immune system activation and IgG antibody generation,

**8. In-vivo models for epidemic and pandemic diseases**

*DOI: http://dx.doi.org/10.5772/intechopen.90073*

infected flies prior to its death [61, 62].

**7.1 Route of inoculum**

**7.2 Flies gender selection**

longer than male flies [65].

ducting preclinical trials [62, 66].

**8.1 HIV models**

**7. Factors contributing to suitable infection model**

Drosophila melanogaster: *A Robust Tool to Study Candidate Drug against Epidemic… DOI: http://dx.doi.org/10.5772/intechopen.90073*

tuberculosis and cholera patients. Similarly rapid loss in weight could be seen in infected flies prior to its death [61, 62].
