2.1. Food Uses

Leaves and twigs of Lippia javanica are used as food additives in Kenya [6] and leafy vegetable in India [12, 13]. Lippia javanica is popular as herbal tea, particularly in Botswana, South Africa, and Zimbabwe [7–11]. Lippia javanica herbal tea is prepared by steeping fresh or dried leaves, stems, or twigs in boiling water and letting them stand for two to five minutes to release flavour, with or without milk and sugar added according to taste. A stronger brew, known as a decoction, is prepared by boiling fresh or dried leaves, stems, or twigs for more than five minutes. The herbal tea prepared from L. javanica leaves, stems, or twigs has a lemon or vanilla aroma and is often used as a common tea (i.e., C. sinensis) substitute or a few leaves, stems, or twigs are added to C. sinensis to provide a lemon or vanilla aroma. According to Sõukand and Kalle [87], herbal tea or tisane is an English term used to denote a decoction or infusion made of herbs for medicinal purposes. When L. javanica is used as medicinal herbal tea, it is consumed for a limited number of days to treat a specific condition like asthma in Zimbabwe [14], bronchitis in South Africa [19], chest pains in Zimbabwe and South Africa [14, 24], colds in Kenya, South Africa, and Zimbabwe [19, 20, 28–30], cough in South Africa and Zimbabwe [19, 20, 30, 53], and other diseases (see Table 1). From literature, it seems L. javanica herbal tea evolved over the years from medicinal tea decoctions or infusions to nonmedicinal uses, where the herbal tea is now drunk for recreation and enjoyment. According to Shikanga et al. [7], L. javanica tea is appreciated throughout its distributional range as a general health tonic and also because it is naturally caffeine-free and has a calming and relaxing effect. Research done by other workers, for example, Manenzhe et al. [2], Shikanga et al. [7], Parrant [8], Olivier et al. [81], Motlhanka and Makhabu [9], and Bhebhe et al. [10, 11], revealed that L. javanica is a popular recreational tea in southern Africa, consumed on a daily basis within a food context, while medicinal infusions or tisanes of L. javanica are taken for a specific medical purpose. During the past 20 years, the use of herbal teas has increased globally [107] because of their functional properties and consumer interest in the health promoting properties of such beverages [108]. The other advantage associated with L. javanica usage is that the leaves can be sun-dried and later boiled in water and drunk as herbal tea [9].

Most of L. javanica used as herbal tea in rural and periurban communities in central, eastern, and southern Africa is still collected from the wild, although small-scale cultivation has become necessary as it is marketed as herbal tea in Botswana under the brand name “Mosukudu” or “Mosukujane” [109] and in Zimbabwe as “Zumbani” (Figure 1(b)). Although considerable quantities of L. javanica are sold in local markets in Botswana and Zimbabwe and also traded on the Internet, there is no data on present production levels, traded volumes, values, and export figures in these two countries. Research by Whiteside [110] showed that sales of L. javanica tea bags generated an income of R20300.00 (US$5718) during 1994/1995 in Botswana. There is increased demand for L. javanica herbal tea especially in the light of growing health consciousness worldwide, with the estimated potential demand for the species and its products around 100 tonnes per year on the local market and 1000 tonnes per year on the export market (http://bio-innovation.org/work/fever-tea-tree/). Considering the rapid growth of the herbal tea industry worldwide and the increasing demand for L. javanica products, there is need for the improvement of L. javanica products as well as development of new products. Therefore, L. javanica has potential to make the transition from limited local use to commercial and international product. Lippia javanica has been identified as one of the few plant species that should be integrated in the domestication process in farming systems in sub-Saharan Africa to support medicinal, nutritional, and income security of local communities [107, 111]. According to Van Wyk [111], L. javanica is of commercial value as herbal tea and health drinks. Therefore, commercialization of L. javanica is unlikely to be viable if the product is sorely harvested from the wild. In the same line commercialization of L. javanica might be more worthy if other products other than tea are derived from the plant.

2.2. Respiratory Problems

The different parts of L. javanica, for example, the leaves and twigs, are used for the treatment of asthma, coughs, colds, influenza, pneumonia, tuberculosis, and bronchial problems in Bangladesh, Botswana, Ethiopia, Kenya, South Africa, and Zimbabwe [14–16, 19, 20, 23, 25, 26, 28–32, 53, 112]. In Bangladesh, leaf infusion of L. javanica is taken orally mixed with 3-4 pieces of cloves of A. sativum, 2-3 times daily as remedy for chest pains [23]. In Ethiopia, leaves of L. javanica are chewed with butter as remedy for chest pains and cough [26]. In India, L. javanica leaf decoction is taken orally as remedy for respiratory disorders [39]. In Kenya, leaves are sniffed [31] or half glass of hot leaf infusion is taken orally three times a day [28, 29] as remedy for colds and cough. Research done by Davids et al. [19] in South Africa revealed that about 50g of leaves is added to a cup of boiling water to produce an infusion which is taken orally as remedy for coughs, colds, and bronchial problems or the infusion is applied to the skin or mixed with Vaseline to make an ointment. In South Africa, leaf or twig decoction is taken orally for asthma, colds, and cough [16, 53], leaves are used in washes and poultices for chest pains [25], and leaves are boiled for 5 minutes and one cup of extract is taken orally thrice a day for chest pains and tuberculosis [24, 42]. According to York [18], two handfuls of L. javanica leaves are boiled in two litres of water and patient is steamed once or twice a day to treat coughs, chest pain, headaches, fever, chills, a sore throat, or a blocked nose. This decoction can also be taken orally by drinking half a cup daily [18]. Alternatively, a handful of L. javanica roots or leaves are mixed with a handful leaves of A. glabratum or B. transvaalensis or B. uniflora or B. cathartica or C. anisata or C. brachiata or C. molle or E. grandis or H. kraussii or Hypoxis spp. or K. mosambicina or P. neochilus or P. guajava or S. serratuloides or T. sericea or T. riparia or T. emetica to treat blocked nose, chest pain, cough, earache, fatigue, fever, influenza, headache, runny nose, sleepless nights, sore throat, tiredness, and tonsillitis [18]. Leaf and stem infusion of L. javanica are taken orally together with A. afra by the Zulu people in South Africa as remedy for bronchial ailments, colds, and cough [20]. “Imbiza,” a popular herbal decoction prepared from L. javanica and C. obliquus, is used by the Zulu people in South Africa as herbal tonic and an immune booster and also for the treatment of cancer, chest pains, colds, diabetes, HIV or AIDS symptoms, skin infections, and tuberculosis [27]. In some communities in South Africa, L. javanica leaf or root infusion is taken orally as remedy for influenza and malaria [33] and respiratory disorders [40, 41]. In Zimbabwe, leaf or root decoction is taken orally or smoke of burnt leaves and roots is inhaled as remedy for chest pains [14] and leaf and twigs are boiled in water and infusion is taken orally as remedy for colds and cough [30]. According to Gelfand et al. [14], Shona people in Zimbabwe rub leaf ointment of L. javanica on the chest and abdomen as remedy for pneumonia and leaf decoction is taken orally and body washed with leaf decoction as remedy for shortness of breath or dyspnoea. In South Africa, a leaf and stem infusion of L. javanica are taken orally together with leaves of A. afra as remedy for measles [20].

Based on literature, inhalation of smoke from L. javanica appears to be a popular remedy for asthma, chest pains, colds, and chronic coughs in Botswana, South Africa, and Zimbabwe [14, 15, 20, 32]. In Botswana, L. javanica leaf infusion vapour is inhaled as remedy for colds and cough [32]. In South Africa, for example, leaves and twigs are burned and smoke is inhaled as remedy for asthma and cough [15] or steam from leaf infusions is inhaled or hot leaf infusions are taken orally against colds and cough [20]. In Zimbabwe, smoke of burnt leaves and roots is inhaled as remedy for chest pains [14].

2.3. Gastrointestinal Diseases

The leaf and root decoction or infusions of L. javanica are used as remedies of the digestive system diseases such as cholera, diarrhoea, and dysentery. For example, in Mozambique, root decoction is taken orally as remedy for a type of diarrhoea commonly known as “chinhamucaca” which is characterized by milky diarrhoea accompanied by vomiting in children [44]. Leaf decoction is used as herbal medicine for diarrhoea in Kenya [113]. In South Africa, the leaves of L. javanica are crushed and mixed with cold or hot water and the mixture is then sieved and a quarter of a cup (75mL) is taken twice a day until diarrhoea subsides [34]. The Venda people in South Africa use leaf infusions as prophylactic against diarrhoea [40]. Research done by Palgrave et al. [37] in South Africa revealed that tea infusions of the L. javanica leaves are used as remedies for HIV/AIDS opportunistic infections such as lung infections and diarrhoea. Previous research in Mozambique [114], South Africa [115], and Zimbabwe [116] showed that gastrointestinal disorders, particularly cholera, diarrhoea, and dysentery are among human diseases often treated with herbal medicines. For those patients diagnosed as having intestinal worms in Venda, South Africa, a leaf infusion of L. javanica leaves is used as an anthelmintic [40]. Therefore, these findings illustrate that herbal medicines including L. javanica can play an important role in basic health care of local communities through treatment and management of cholera, diarrhoea, and dysentery.

2.4. Fever, Malaria, and Insect Repellent

Traditionally, L. javanica is commonly used to treat fever and malaria and repel insects throughout its distributional range [4, 14, 16, 17, 33–35, 40, 48–50, 58–60]. In South Africa, a decoction of fresh or air dried leaves is used to wash or steam body parts infested with lice [50]. In India, the whole plant is used to repel lice in poultry [61]. In South Africa and Zimbabwe, whole plant or leaves are burnt to repel mosquitoes [4, 34, 35, 48, 49, 58]. In South Africa and Zimbabwe, L. javanica is widely used to get rid of ticks and other ectoparasites; for example, ticks are sprayed with crushed leaves mixed with water or twigs are used as bedding in fowl runs [58–60]. Leaf and twig decoction of L. javanica are taken orally as remedy for fever [16]. The Venda people in South Africa use leaf infusions of L. javanica as prophylactic against malaria [40]. In Zimbabwe, leaf decoction is taken orally as remedy for fever [14].

Lippia javanica is also cultivated on a commercial scale by a rural community in Giyani, the Limpopo province, South Africa, for the production of mosquito-repellent candles [117]. Clinical studies using human volunteers showed that L. javanica repels no less than 95% of mosquitos, whereas most mosquito repellents repel only 42% of them [118]. Based on these findings, the Council for Scientific and Industrial Research (CSIR), South Africa, signed a benefit sharing agreement with traditional healers allowing for the commercial cultivation of L. javanica aimed at establishing an indigenous oil industry for rural development and large-scale production of antimosquito candles and other insect repellents. The mosquito repellent is registered as a patent under the Fertilisers, Farm Feeds and Stock Remedies Act (Act 36 of 1947) as a pest repellent [119]. These findings and the establishment of a large-scale production of antimosquito candles and other insect repellents strengthen the view that L. javanica is a potential source of antipesticidal agents and to some extent validate the traditional use of the plant species for insect pest control. Pesticidal plants such as L. javanica are increasingly being used as alternatives where synthetic products are unaffordable or are not available or are ineffective. A number of studies have indicated that the use of L. javanica as a pesticide is a long-standing tradition passed down from generation to generation [120].

2.5. Wounds, Injuries, Pain, and Skin Infections

Lippia javanica is used as remedy for a variety of skin infections and injuries in Kenya, South Africa, Swaziland, and Zimbabwe. In South Africa, leaf infusions are used to treat skin disorders, such as boils, chicken pox, febrile rashes, heat rashes, measles, scabies, scratches, and stings [20, 21, 40, 50, 54]. In Kenya, about 50g of fresh leaves is wrapped around a fresh wound to enhance healing [57] and, in South Africa, leaf infusions are taken orally as remedy for wounds [54]. In South Africa, powder from burnt roots of L. javanica is applied to scarifications made around sprained joints to facilitate healing [20]. In Kenya and Zimbabwe, leaf infusion is taken orally to treat measles or a patient is washed with leaf infusion [14, 38]. The Zulu people in South Africa take a mixture of chopped handful leaves of L. javanica with the same amount of bark of A. burkei, O. engleri, S. birrea, S. cordatum, and T. elegans boiled in two litres of water as an enema for the treatment of sores [56]. In Swaziland, about 30g of L. javanica leaves and similar amount of Acanthospermum australe Kuntze are boiled in 5 litres of water and decoction is taken as remedy for sores [55]. In Zimbabwe, root ashes of L. javanica mixed with fat are applied to the skin of a patient with scabies [14]. Wound healing is a process which involves distinct overlapping phases of coagulation, inflammation, proliferation, and tissue remodelling [121]. The same authors argued that a set of complex biochemical events takes place in a closely orchestrated cascade to repair the wound and any errors in the wound healing process can lead to delayed healing or formation of hypertrophic scars. Abubakar [122] argued that colonization of wounds by opportunistic microorganisms usually delays the wound healing process and/or may lead to infectious condition. Therefore, application of L. javanica on wounds and skin infections leads to disinfection, debridement, and provision of a suitable environment for aiding the wound healing process. Lippia javanica has potential for therapeutic use in wound and skin diseases management, but there is need for research on the safety, phytochemistry, and biological properties of the species.

2.6. Ethnoveterinary Uses

The leaves, stems, twigs, and whole plants of L. javanica are used as ethnoveterinary medicine in India, Kenya, South Africa, and Zimbabwe. The Xhosa people in the Eastern Cape province, South Africa, use L. javanica leaves for the disinfection of meat that has been infected with anthrax [20]. In Kenya, the stem of L. javanica is used to preserve milk by applying it to the gourd before milk fermentation [62]. In India, whole plants are used as lice repellants while, in South Africa and Zimbabwe, crushed leaves mixed with water are used to get rid of ticks and twigs are used as bedding in fowl runs to get rid of ectoparasites [58–60].

4.1. Anticancer Activity

Fouche et al. [140] reported anticancer activity of dichloromethane root extract of L. javanica against three human cells, exhibiting TGI value of 1.82μg/mL for breast MDA-MB-435, 1.86μg/mL for breast MDA-N, and 2.09μg/mL for melanoma MALME-3M. Based on literature, a couple of terpenoid compounds that have been isolated from L. javanica are known to have antitumor properties. For example, linalool 120 is known to have antitumor activity which plays a protective role against hepatotoxicity and the compound has anti-inflammatory activities as well [151]. Research by Yang et al. [152] showed limonene 92 to have inhibitory effect on pancreatic and mammary tumors. Another terpenoid compound, α-pinene 44, is known to inhibit translocation of NF-κB or p65 protein into nuclei of LPS-stimulated THP-1 cells [153]. These findings serve as a scientific validation for the use of L. javanica as a component of a herbal concoction known in KwaZulu Natal province as “imbiza,” prepared by mixing L. javanica with C. obliquus as herbal medicine for cancer [27].

4.2. Antidiabetic Activity

Arika et al. [141] determined the in vivo antidiabetic activity of aqueous leaf extracts of L. javanica in white male alloxan-induced albino mice. The aqueous leaf extracts of L. javanica at all dose levels significantly lowered the blood glucose levels in both oral and intraperitoneal routes. The antidiabetic effect of L. javanica could have been due to the observed presence of flavonoids. The polyhydroxylated flavonol enhances lipogenesis and glucose uptake in the adipocytes and flavanoids have demonstrated insulinmimetic properties as the compound is known to be effective at controlling blood sugar levels. These findings strengthen the view that L. javanica is a potential source of antidiabetic agents and to some extent validate the traditional use of the plant species mixed with C. obliquus to form a herbal concoction known in KwaZulu Natal province, South Africa, as “imbiza” used against diabetes [27].

4.3. Antimalarial Activity

Govere et al. [142] found that topical application of L. javanica alcohol extract leads to 76.7% protection against Anopheles arabiensis for 4 hours. Lippia javanica has been used as a mosquito repellent by the rural communities in Zimbabwe for a long time and previous studies have shown that essential oils from the species have very strong and lasting repellent activity against female A. arabiensis [64]. Research by Lukwa et al. [4] revealed that topical application of 5mg/cm² of L. javanica leads to 100% protection against Anopheles aegypti for 8 hours. Mavundza et al. [154] screened dichloromethane and ethanol leaf extracts of L. javanica for adulticidal activity against A. arabiensis. The authors observed dichloromethane and ethanol activities of 45% and 55% mosquito mortality, respectively. These findings strengthen the view that L. javanica is a potential source of antimalarial agents and to some extent validate the traditional use of the plant species as mosquito repellent in India [47], South Africa [34, 49, 58], and Zimbabwe [4, 48].

4.4. Antioxidant Activity

Leaf infusions of L. javanica exhibited antioxidant activity with EC₅₀ value of 358μg/mL and contained 14.8mg/mL of dry weight gallic acid equivalent phenolic compounds [7]. The EC₅₀ value of 358μg/mL obtained for L. javanica by Shikanga et al. [7] compares well to those of many commercial teas, including antioxidant capacity of Rooibos Fresh Pack™ herbal teas (A. linearis) with the best antioxidant activity of 333μg/mL. The high antioxidant activities displayed by L. javanica infusions can be partially attributed to the high levels of verbascoside 2 (1.5mg/g dry weight) reported by Olivier et al. [81] in the leaf extract of the species. Earlier research by Muchuweti et al. [125] reported 74.4% inhibition of the DPPH radical by an ethanolic leaf extract of L. javanica. Lekganyane et al. [75] reported antioxidant activity in L. javanica and the acetone extracts of the species displayed antioxidant activity on BEA chromatogram [77]. Bhebhe et al. [10] reported the antioxidant activities of L. javanica based on the DPPH, reducing power and inhibition of phospholipid peroxidation assays. Free radical scavenging activity of L. javanica is attributed to phenolic compounds since these compounds have an ideal structural chemistry for free radical scavenging activity [155]. Bhebhe et al. [11] determined the effect of several solvents on the free radical scavenging activity of L. javanica using the DPPH assay. Free radical scavenging activity expressed as IC₅₀ ranged from 0.022 ± 0.001g/mL to 0.066 ± 0.001g/mL; see Table 4.

4.5. Antiplasmodial Activity

Prozesky et al. [144] evaluated L. javanica leaf acetone extract for in vitro antiplasmodial activity using PfUP1, a chloroquine resistant strain of the malaria parasite Plasmodium falciparum by means of the flow cytometric test. The IC₅₀ value for L. javanica was 4.26μg/mL. Manenzhe et al. [2] evaluated essential oil, piperitenone 162, isolated from L. javanica for antiplasmodial activity using chloroquine diphosphate as positive control and found it active against a chloroquine sensitive strain of P. falciparum in micromolar concentrations with IC₅₀ of 8μg/mL. Clarkson et al. [80] evaluated L. javanica roots and stems extracts for in vitro activity against P. falciparum using the parasite lactase dehydrogenase (pLDH) assay and chloroquine diphosphate (Sigma) as the positive control. The dichloromethane, methane, and water extracts showed IC₅₀ values ranging from 3.8 to >100μg/mL; see Table 4. Omolo et al. [145] screened the essential oil of L. javanica for fumigant toxicity to Anopheles gambiae which exhibited LD₅₀ of 4.3 × 10⁻³mgcm⁻³. Ayuko et al. [79] showed that L. javanica root extracts have antiplasmodial activity against P. falciparum with IC₅₀ ranging from 1.35 to 18.59μg/mL; see Table 4. Lippialactone 21, derived from the ethyl acetate extract of aerial parts of L. javanica, exhibited some activity against the chloroquine sensitive D10 strain of P. falciparum with an IC₅₀ value of 9.1μg/mL and is also mildly cytotoxic [84]. Compared to chloroquine, the compound is approximately 2000 times less active against the D10 strain of P. falciparum [84].

4.6. Antimicrobial Activities

Lippia javanica is widely used in the treatment of a wide range of infectious diseases caused by microorganisms. Viljoen et al. [3] determined the antimicrobial properties of L. javanica by evaluating the time kill studies of the species' essential oil using the disc diffusion assay on three respiratory pathogens Klebsiella pneumoniae, Cryptococcus neoformans, and Bacillus cereus. This study showed that the killing rate was greatest for K. pneumoniae followed by C. neoformans and very little reduction of microbial populations was observed for B. cereus. The efficacy of L. javanica oil for K. pneumoniae showed a killing rate within 30 minutes for the concentrations 0.25, 0.5, 0.75, and 1%, C. neoformans showed a killing rate for concentrations 0.5, 0.75, and 1% within 1 hour, and the lowest concentration of 0.25% took 8 hours before a bactericidal effect was noted while B. cereus showed some reduction in colonies [3]. The positive antimicrobial activity of L. javanica as revealed by the time kill study could be attributed to linalool 120 which averages between 65 and 70% in yield [3, 5, 88, 90] and has known antimicrobial properties [93, 156–159]. These findings somehow corroborate the traditional use of L. javanica as herbal medicine for a wide range of bacterial and fungal respiratory ailments indicated in Table 1.

Manenzhe et al. [2] evaluated essential oil, piperitenone 162, isolated from L. javanica for antibacterial activity on cultures of Bacillus subtilis, Staphylococcus aureus, and Escherichia coli using imipenem, cefazolin, and ampicillin as positive controls. The authors found piperitenone 162 to inhibit S. aureus and E. coli at 1% dilution. Acetone, hexane, and methanol leaf extracts and essential oil isolated from L. javanica showed some activity against fifteen Gram-positive and Gram-negative bacteria with MIC values ranging from 1.5 to >12mg/mL [60]; see Table 4. In a similar study, Samie et al. [73] demonstrated that a pure compound piperitenone 162 isolated from L. javanica has antibacterial activities against Acinetobacter calcoaceticus, Micrococcus kristinae, Salmonella typhi, and S. aureus using dimethyl sulphoxide and kanamycin as controls, with MIC values ranging from 12 to 50μg/mL; see Table 4. Shikanga et al. [7] evaluated the antibacterial activity of L. javanica methanolic leaf extract against S. aureus, Enterococcus faecalis, E. coli, and Pseudomonas aeruginosa using the serial microdilution method with gentamycin (Virbac®) and acetone as positive and negative controls, respectively. Lippia javanica displayed antibacterial activities with MIC values ranging from 0.13 to 0.42mg/mL against all four pathogens; see Table 4. The obtained minimum inhibitory concentrations are promising, since natural products with MIC values below 1mg/mL are generally considered to be noteworthy findings [160]. Lippialactone 21, derived from the ethyl acetate extract of aerial parts of L. javanica, exhibited some activity against the E. coli and S. aureus at a concentration of 10mg/mL [84]. Lekganyane et al. [75] reported antibacterial activity of L. javanica acetone leaf extracts against E. coli, E. faecalis, P. aeruginosa, and S. aureus with MIC values ranging from 0.32 to 0.64mg/mL and total activity of the same species ranging from 127 to 253mg/mL; see Table 4. Methanol and water leaf extracts of L. javanica exhibited some antiproteus activity against Proteus mirabilis and Proteus vulgaris with MIC values <2000μg/mL with standard discs of ampicillin (2μg) and chloramphenicol (10μg) as positive controls [74]. Some of the antibacterial properties of L. javanica can be attributed to the phytochemical constituents of the species; for example, the phenolic compound apigenin 7 is a well-known antibacterial agent [7, 134]. Apigenin 7 was shown to be highly active against Vibrio cholera and E. faecalis [161], while Basile et al. [162] reported the inhibition of S. typhi, P. mirabilis, and P. aeruginosa by the compound. Therefore, results from these antibacterial evaluations of L. javanica give credence to the use of the species' infusions against bacterial infections and other related diseases.

Shikanga et al. [126] investigated the antifungal activities of leaf extracts and essential oil compounds isolated from L. javanica leafy extracts against a Guazatine®-resistant strain of Penicillium digitatum. The methanolic leafy extracts, isoverbascoside 3 and verbascoside 2 compounds, isolated from L. javanica inhibited fungal growth at concentrations above 0.6mg·mL⁻¹, causing significant inhibition of mycelial growth. Verbascoside 2 is well-known for its antimicrobial properties and has been found to inhibit viruses, bacteria, and fungi [163]. Similarly, Samie et al. [143] investigated antifungal effects of acetone and hexane leaf extracts of L. javanica against Candida albicans, Candida krusei, and C. neoformans isolated from AIDS patients using the microdilution method with nystatin, Roche, and DMSO as positive and negative controls, respectively. Noteworthy moderate antifungal activities were recorded from C. krusei with MIC value of 1.88mg/mL and other recorded MFC and MIC values for other species ranged from 1.88mg/mL to >7.5mg/mL; see Table 4. Thembo et al. [76] investigated the antifungal activity of aqueous and organic extracts of L. javanica using a serial microdilution assay. Generally, extracts of L. javanica exhibited weak activity; see Table 4.

4.7. Antimycobacterial Activity

Mujovo et al. [83] evaluated L. javanica compounds against a drug-sensitive strain of Mycobacterium tuberculosis using the radiometric respiratory techniques. Of all the isolated compounds, only one triterpenoid carboxylic acid, euscaphic acid 172, exhibited antimycobacterial activity with MIC value of 50μgmL⁻¹ against this strain. In a similar study, the leaf extract of L. javanica exhibited antimycobacterial activity against M. smegmatis in an evaluation which used microdilution assay and rifampicin as control [77]. Acetone extract was the best extractant with MIC value of 0.47mg/mL; it extracted antibacterial agents which was indicated by the lowest MIC value [77]. Masoko and Nxumalo [77] also evaluated the total activity of L. javanica which averaged 13mL/g suggesting that the extract prepared from one gram of L. javanica could be diluted to a volume of 13mL and will still inhibit M. smegmatis efficiently. According to Semenya and Maroyi [115], tuberculosis caused by M. tuberculosis is a serious disease requiring effective strategies and tools to control and manage it. Therefore, preliminary evaluations done by Mujovo et al. [83] and Masoko and Nxumalo [77] serve as a scientific validation for the use of L. javanica in traditional medicine for treatment of tuberculosis and other respiratory ailments in South Africa [24, 27, 115] and Uganda [43] as well as their efficiency in tuberculosis drug discovery.

4.8. Antiviral Activity

Mujovo et al. [83] found that (E)-2(3)-tagetenone epoxide 42 and piperitenone 162 inhibited the HIV-1 reverse transcriptase enzyme by 91% and 53%, respectively, at 100μgmL⁻¹ based on a nonradioactive HIV RT colorimetric ELISA kit. Little is known about the HIV RT activity of L. javanica extracts or compounds, but flavonoids are known to be active against viral RT and also as potent inhibitors of the cellular alpha and beta DNA polymerase [83], while luteolin 12 is active against HIV RT [164, 165]. Lippia javanica is traditionally used to treat HIV/AIDS symptoms in South Africa [65, 66] and several viral and HIV/AIDS opportunistic diseases and infections such as bronchitis [15, 19–22], chicken pox [50], diarrhoea [17, 34, 37, 44, 113], measles [14, 20, 38], pneumonia [14], shingles [15], and venereal diseases [44]. Despite significant advances in the utilization of L. javanica in southern Africa over the years for numerous viral diseases (Table 1), very little antiviral evaluations have been done on crude extracts and purified compounds of the species. There is need, therefore, for more pharmacological research as L. javanica could be harbouring potent (RT) inhibitors which could be useful for the development of new pharmaceutical products important for use against viral diseases and infections.

4.9. Pesticidal Effects

Magano et al. [95] evaluated the repellent effects of hexane extracts of L. javanica essential oil using the in vitro tick climbing repellency bioassay on adults of Hyalomma marginatum rufipes Koch ticks. The authors found that 107mg/mL caused repellency index of 100% at one hour and 30 minutes. In a similar study by Madzimure et al. [120], L. javanica aqueous leaf extracts at 10% and 20% w/v were effective at controlling cattle ticks (Amblyomma species, Boophilus species, Hyalomma species, Rhipicephalus appendiculatus, and Rhipicephalus evertsi evertsi) and were as good as the positive control amitraz-based acaricide Trickbuster®. These authors found no parasites on microscopic examination of the Giemsa-stained thin blood smear collected from treated cattle implying that the animals did not suffer from clinical tick-borne diseases. Similarly, Nyahangare et al. [59] tested the pesticidal activity of L. javanica water extracts against cattle ticks. The authors found no significant difference between cattle treated with a commercial synthetic acaricide and those under L. javanica treatment. Martinez-Velazquez et al. [166] evaluated pesticidal effects of two essential oils, namely, γ-terpinene 82 and ρ-cymene 99, isolated from Lippia graveolens Kunth against 10-day-old Rhipicephalus (Boophilus) microplus (Canestrini) tick larvae using the larval packet test bioassay. The two essential oils produced high mortality ranging from 90 to 100% in all tested concentrations of 20 to 1.25% (v/v). Therefore, L. javanica can provide an effective tick control option where synthetic products are unavailable or unaffordable particularly in remote rural areas in sub-Saharan Africa. Lippia javanica is popular for tick control and management among resource-poor smallholder farmers in South Africa [58, 95] and Zimbabwe [59, 60, 120]. While these preliminary evaluations may serve as confirmation that L. javanica has some bioactivities against ticks, a comprehensive method of tick control is required for the resource-constrained smallholder farmers based on ethnopharmacological properties of L. javanica.

McGaw et al. [146] screened L. javanica for the anthelmintic test systems using the free living nematode Caenorhabditis elegans. The crude ethanol and hexane extracts showed some activity at a concentration of 2mg/mL, with the 7-day incubation assay appearing to be more sensitive than the shorter assay. Earlier research by Mwangi et al. [1] indicated that L. javanica was active against Aedes aegypti larvae and Sitophilus zeamais Motschulsky (maize weevil). Katsvanga and Chigwiza [147] reported that L. javanica is an effective natural pesticide which can be used to control aphid species (Brevicoryne brassicae). In their study, Katsvanga and Chigwiza [147] found that 1:1 powdered aqueous leaf extract of L. javanica reduced B. brassicae by 53.2% against 78.3% and 96.7% of two synthetic pesticides, Aphid kill and Bexadust “L,” respectively. Chikukura et al. [149] found L. javanica powdered leaf extracts to have insecticidal properties with potential to control grain damage by 21–33%. Mashela et al. [148] reported that the application of ground L. javanica leaves to soil in nematode-infested (Meloidogyne incognita) pots reduced the nematode numbers by 79–92% and significantly increased fresh fruit yield, dry shoot mass, plant height, and stem diameter of the tomato plants, as well as levels of potassium, nitrogen, and manganese in leaf tissue. Muzemu et al. [150] evaluated water extracts of L. javanica leaf powder for pesticidal effects against rape (Brassica napus L.) aphids, B. brassicae, and tomato (Solanum lycopersicum Lam.) red spider mites, and Tetranychus evansi as alternatives to conventional pesticides. Lippia javanica reduced B. brassicae and Tetranychus evansi by 12.5% and 63%, respectively [150]. The study demonstrated that L. javanica has pesticidal effects on B. brassicae and T. evansi. The reduced number of B. brassicae and T. evansi could be due to L. javanica's extracts having repellent, toxic, and antifeedant effects since the species has essential oils with pesticidal properties [2]. Therefore, these findings indicate that L. javanica has both nematicidal and plant growth-promoting properties.

4.10. Toxicity and Cytotoxicity Activity

Lippia javanica is known to cause liver damage and photosensitisation in livestock, resulting in stock losses [167]. Triterpenoids isolated from the genus Lippia are icterogenic and cause jaundice as a result of liver damage [167]. The characteristic swelling, yellowing, and later peeling of unpigmented skin are due to the presence of phylloerythrin, a photodynamic porphyrin that reacts with sunlight and causes severe cell damage [167]. The compound is normally formed when chlorophyll is broken down by microorganisms in the rumen, but it now accumulates in the liver as a result of the damage caused by triterpenoids [167]. In view of the known toxicity of Lippia species, the prolonged use of high doses of L. javanica is potentially harmful [167]. Lippia javanica showed low toxicity after 48h exposure with the percentage of mortality below 50% [74].

Ayuko et al. [79] evaluated the toxicity of L. javanica using a brine shrimp cytotoxicity assay with LC₅₀ value of 1138 ± 1.33μg/mL. Ayuko et al. [79] found the cytotoxicity to antiplasmodial activity ratios for the methanolic extracts of the two tested strains to be 843.0 and 650.3, and since these are greater than 100, it may be concluded that the extracts are of low toxicity. Samie et al. [73] demonstrated that a pure compound piperitenone 162 isolated from L. javanica essential oil has low cytotoxicity activity against intestinal adenocarcinoma cells (i.e., the HCT-8 monolayers with IC₅₀ of 265.6 ± 5.3μg/mL). Lukwa [64] evaluated the toxicity of L. javanica aqueous leaf extracts using sexually mature BALB/c mice with the placebo as control. Within 48 hours, all mice fed with the L. javanica leaf aqueous extract at 12.5–37.5% v/v were lethargic, and the overall mortality was 37.5%. Previous research by Manenzhe et al. [2] showed that hydrodistillation of L. javanica leaves, flowers, and stems produced oil that was poisonous against P. falciparum when diluted to 1% (v/v). These findings imply that, despite its apparent safety, water extracts of L. javanica leaves may have deleterious health implications on humans and animals if consumed at very high doses.

Many compounds that have been isolated from L. javanica including phenolic glycosides, flavonoids, and essential oils are not known to have acute toxic properties with the exception of icterogenin 173. Icterogenin 173 has been shown to inhibit biliary excretion in rabbits [168]. Reports in literature indicate that the consumption of xanthine 22 has resulted in mammalian toxicity. According to Madzimure et al. [64], xanthine 22 is a demethylated derivative of caffeine with pharmacological actions such as central nervous system (CNS) stimulation, relaxation of smooth muscle (especially bronchial muscle), myocardial stimulation, peripheral vasoconstriction, and diuresis. Considering the widespread use of L. javanica as herbal tea and medicine, it is important to determine if any toxicological effects can occur from its chronic or subchronic usage.

The author would like to express his gratitude to the National Research Foundation (NRF) and Govan Mbeki Research and Development Centre (GMRDC), University of Fort Hare, for financial support to conduct this research.