**5. Challenges and future prospects**

interference, incomplete protection, and dose sufficiency [35] makes the search for new anti-

In Malaysia, the National Dengue Strategic Planning 2015–2020 (the Sixth Strategy: Dengue Research) highlights the importance of research aimed at enhancing the effectiveness, costeffectiveness, sustainability, and the scale of existing interventions, as well as producing ideas and new methods, while promoting collaboration with relevant agencies. In this regard, it is anticipated that comprehensive research focusing on the local natural heritage, including the

**activity**

Anti-dengue activity against the primary dengue vector *Aedes aegypti*

Anti-DENV-2 activity by inhibiting the production of viral RNA and viral protein

Anti-dengue activity against different stages of DENV-2 infection and replication cycle

**Reference**

[38]

[39]

[40]

**Plant Secondary metabolites Biological** 

Andrographolide (class: terpenoid)

Pheophorbide (class: chlorophyll)

Quercetin (class: flavonoid)

**Table 3.** Selected secondary metabolites from plants with effects against dengue or its vector.

viral agents imperative.

106 Secondary Metabolites - Sources and Applications

*Andrographis paniculata* **(Hempedu Bumi)**

*Clinacanthus nutans (Burm.F)* **(Belalai Gajah)** leaves

*Psidium guajava* **(Jambu Batu)** leaves

leaves

Despite a more concerted efforts and strategic approach to add value to the country's herbal industry, the desired output has not reached its optimum. The main challenges including the lack of good research documentation, monographs, standardization in farming practices (good agricultural practices, GAP), good laboratory practice (GLP), and development and commercialization of products still persist. Further, the increased harvesting of medicinal herbs raises the concerns about the extinction of plant populations and degradation of natural plant habitat causing shortage in plant raw materials which may affect the effort to reach high mass production of secondary metabolites. To this end, biotechnological applications such as plant tissue cultures have been recognized an alternative tool for scaling-up the production of secondary metabolites. However, challenges inherent in plant tissue cultures must be overcome in order for it to contribute to significant cost-effective production of secondary metabolites. This includes the understanding of the secondary metabolites and their metabolic pathways, identification of the highest yielding populations, control of specific gene expression and regulatory enzymes, and the use of economic sterile bioreactors. Leveraging the country's wealth of flora species, a continuous effort from the government, academia, and industry to further nurture and uphold the herbal industry is indispensable.
