Available online on 15.08.2021 at http://jddtonline.info

Journal of Drug Delivery and Therapeutics

Open Access to Pharmaceutical and Medical Research

Copyright  © 2021 The  Author(s): This is an open-access article distributed under the terms of the CC BY-NC 4.0 which permits unrestricted use, distribution, and reproduction in any medium for non-commercial use provided the original author and source are credited

Open Access  Full Text Article                                                                                                                                         Review Article 

Systematic Review of Plants Used Against Respiratory Diseases Related to COVID-19 in Africa

 Gabriel Agbor Agbor*, Rosette  Christelle Ndjib

Centre for Research on Medicinal Plants and Traditional Medicine, Institute of Medical Research and Medicinal Plants Studies, Cameroon

Keywords: Respiratory diseases, Medicinal plants, COVID-19

INTRODUCTION

Respiratory diseases are known to affect the airways including the nasal passages, bronchi and lungs. It is very often difficult to classify them because they have different levels of severity and are closely dependent on the patient's age. They can be bronchitis, pneumonia, asthma, tuberculosis, sinusitis, and rhinitis representing the main factors of morbidity and mortality in both developed and developing nations of the world ¹ Respiratory infections account for up to 38.6% of infectious diseases and are responsible for the death of around 14.9% of children in Africa ².

Coronaviruses are emerging and reemerging enveloped RNA viruses that are distributed broadly among humans, mammals and birds. Coronaviruses vary significantly in the pathogenicity, and include highly pathogenic species such as MERS-CoV and COVID-19, and relatively harmless species such as the common cold. Severe Acute Respiratory Syndrome Corona Virus (SARS-COV) is the causal agent of the outbreaks in 2002, 2003 in China ³. In December 2019, a new epidemic of SARS-COV was detected in several local health facilities from patients with pneumonia in Wuhan, Hubei Province, China ³. COVID-19 is a species of coronavirus (CoVs), an etiologic agent which can systemically cause disorder in the respiratory and digestive tract, resulting in severe infections in both humans and animals ⁴. Currently, no specific therapies for COVID-19 are available and investigations regarding the treatment of COVID-19 are still limited to preventive and supportive therapies, designed to prevent further complications and organ damage ⁵. The main symptoms described for COVID-19 were those of malaria (fever, fatigue, body aches, etc.), accompanied by symptoms of respiratory disorders (dry cough, breathing difficulties, chest pain, sore throat, etc.) and flu ⁶. After the panic caused by the first cases of contamination in Cameroon in March 2020, the population in search of preventive and even curative measures for COVID-19, flocked the traditional pharmacopoeia ⁷ in search of traditional medicine which have properties against any of the symptoms. The plants most in demand were largely those with anti-influenza, antimalarial and immunomodulatory properties including those with reported effects on respiratory disorders.

In another study, some plant-sourced antioxidant and immune-boosters, kaempferol, quercetin, luteolin-7-glucoside, demethoxycurcumin, naringenin, apigenin-7-glucoside, oleuropein, curcumin, catechin, epicatechin-gallate, zingerol, gingerol, and allicin were investigated as potential inhibitor candidates for COVID-19, in comparison to antiretroviral protease inhibitors ⁸. It was found that these plant products could act as potential inhibitors, meaning the source plants could be exploited as potential candidates for the development of improved traditional medicines (ITMs) as inhibitors of COVID-19.   

The use of traditional medicine dates back to prehistoric times and remains the major accessible and affordable treatment for the population in African countries. Today medicinal plants which are the main component of traditional medicine have been transformed into conventional drugs that are sold in pharmacies worldwide. Many other plants are currently undergoing investigation to ascertain their therapeutic efficacies and safety. Medicinal plants have long been known for their curative or protective effects against a broad range of microorganisms, such as viruses, protozoa, bacteria and parasites ^9-11. There are reports stating the protective effect of plant extracts against viral diseases, such as HIV 1&2; Herpes simplex virus, Hepatitis B & C virus ^12-14 just to name a few.  Considering that COVID-19 is a respiratory disorder, the present study systematically reviewed the plants used in Africa for the treatment of respiratory disorders.

1. METHODOLOGY
   1. Collection of bibliographic data

The scientific articles selected were based on relation to respiratory diseases published within the last ten years (2011-2021). The open access search engines consulted included: Science Direct, Research gate, Google Scholar, Pubmed, Web of Science and Scopus. The plants listed were classified according to the country of origin of the author of the publication, the botanical family and the respiratory pathology being treated. Thus, a plant which treats ‘n’ distinct respiratory diseases will be cited ‘n’ times and is considered to most likely be effective against the coronavirus. Ethnobotanical indices were calculated to determine which plants may have their therapeutic potential related to management of COVID-19.

Fr = Nc / Nt

where Nc is the number of citations of the species and Nt the total number of citations of all species;

(Nc / N) - (Ncm / Nt)

Where Nc is the number of citations of a plant in the treatment of a respiratory pathology;

 N: the total number of citations of all the plants used in the treatment of this respiratory pathology; 

Ncm: the number of citations of the plant for all respiratory diseases and 

Nt: the total number of citations.

PI = 0 if (Nc / N) - (Ncm / Nt) <0 for zero performance

PI = 1 if 0 <(Nc / N) - (Ncm / Nt) ≤ 1/3 for average performance

PI = 2 if 1/3 <(Nc / N) - (Ncm / Nt) ≤ 2/3 for good performance

PI = 3 if (Nc / N) - (Ncm / Nt)> 3/3 for excellent performance

S = I1 / I2

With I1: Number of publications (on the bibliographic review used) which mention the use of the species in the management of respiratory diseases I2: Number of total publications.

The listed plants were then recorded on a Microsoft Excel 2013 spreadsheet and the ethnobotanical indices calculated. Descriptive statistics was used to express the data obtained (Tables and Figures).

1. RESULTS AND DISCUSSION
   1. Bibliographic information on the scientific publications selected

The bibliographic search listed out seventy-five (75) publications from African authors. Of these, fourteen (14) discussed the use of medicinal plants in the management of respiratory diseases in Africa. The publications had authors from seven (07) African countries among which Benin (64), Cameroon (41), Morocco (33) and Gabon (27) were the most represented (Figure 1).

The fourteen (14) articles that reported the use of medicinal plants in the management of respiratory disorders were further analyzed. In a similar study in West Africa twelve articles were selected to produce a rich repertoire of plants used against respiratory diseases ¹⁷. In their publication they identified African authors as follows: Benin (64), Cameroon (41), Morocco (33) and Gabon (27) whose publications discussed the use of plants for treatment of respiratory disorders. Thus, in the study of Haidara et al. ¹⁷ Benin had the highest number of authors reporting on medicinal plants and respiratory disorder followed by Cameroon and then Morocco in the third place. This result corroborated our data that presents Benin as the country with the most cited authors with interest in medicinal plants for the management of respiratory disorders. This could be justified by the fact that the Beninese is much more attached to traditional medicine with plants as the main ingredient. This data is also indicative that there is a high prevalence of respiratory disorder and that it is of importance to Benin researchers.

Figure 1: Spectrum of the authors' countries of origin according to the number of citations.

Figure 2: Spectrum of references used as a function of the number of citations.

Figure 2 presented the spectrum of references reviewed in this study and their number of citations. Of the fourteen (14) references retained for this review, Kouchadé et al. ¹⁸ was the most cited revealing several plants used against respiratory diseases. Kouchadé et al. ¹⁸ cited over 55 times and Mathouet et al. ¹⁹ cited over 30 times signifies the importance and impact of the results of these groups of researchers in the use of medicinal plants against respiratory diseases. 

In the 14 articles reviewed, one hundred and seventy-nine (179) research citations were registered on the use of plants species in the treatment of respiratory disorders in Africa. A total of one hundred and forty-three (143) plants species were reportedly used in Africa in the management of respiratory diseases. However, we reported only those plants species that were cited at least twice (Figure 3). The most cited plants across board were: Ocimum gratissimum L. (04 citations), Entandrophragma cylindrium (Sprague), Scyphocephalium ochocoa Warb. Rubia cordifolia and Allium sativum L. (03 citations each) (Figure 3). A similar study in West Africa recorded 145 species while North Africa reported 57 species implicated in the treatment of respiratory disorder ^{20, 21}. Equally, 24 species were reported in Gabon to have therapeutic effect on respiratory disorders ¹⁹. Hence West Africa may have a well-organized traditional medicine system that promotes traditional medicine.

Figure 3: Spectrum of plants citations used in the treatment of respiratory diseases in Africa.

Figure 4: Frequency of citation of plants families in the management of respiratory disorder.

Sixty (60) plant families were reported in the present study. Twenty-three (23) families were cited at least three times. Amongst the 23 families Lamiaceae (18 citations) had the highest citation for respiratory disorders followed by the Fabaceae (08) and Myrtaceae (08) and then Solanaceae (07) (Figure 4). The rest of the families had below 7 citations. In African traditional medicine, the population uses plants that are within their immediate surrounding for treatment. This is the case of the Lamiaceae for Morocco and the Fabaceae for the countries of Central and West Africa. A typical example is that of Alchornea cordifolia that finds application as therapeutic agent in the respiratory system ²².

Figure 5: Number of plants cited for the treatment of respiratory disorders.

Fifteen respiratory conditions were listed from the literature search (Figure 5). Of the fifteen respiratory conditions listed, the generalized respiratory infections appear first (43 citations), followed by rhino-bronchitis (42 citations), cough (30 citations), lung infection (20 citations), asthma (19 citation) and angina (10 citations). These respiratory infections are those mostly seen in moderate to severe COVID-19 infection. One of the most important respiratory pathogens in COVID-19 is the human rhinovirus known to cause rhino-bronchitis ²³ meanwhile cough is one of the most common presenting symptoms of COVID-19, along with fever and loss of taste and smell ²⁴. When persist for weeks or months after SARS-CoV-2 infection, cough is accompanied by chronic fatigue, cognitive impairment, dyspnea, or pain ²⁴. The situation of COVID-19 worsens in patients with preexisting conditions such as asthma and can be very fatal ²⁵. COVID-19 infection gets worst with lung infections such as pneumonia. This is because the lungs responsible for gaseous exchange are compromised by pneumonia and COVID-19. Plants with therapeutic effects against these conditions could be of help to COVID-19 patients.

1. Ethnobotanical clues on the uses of plants in the management of respiratory tract diseases.
   1. Citation Frequencies and Scores

The frequencies and citation scores obtained for the different plants were presented in Table 1.

Table 1: Frequencies and citations scores of plants used against respiratory diseases 

Citation frequency = No citation of a species/No. of citation of all samples

The relative frequency of plant species is the ratio between the number of citations of the species and the total number of citations of all species. Hence the lower the frequency the lower the importance of the species. It emerged from this table that almost all of the plants listed have a low frequency, low citations and a low convergence score. However, certain plants were able to stand out: Ocimum gratissimum (score of 0.286 and 0.022 frequency), Allium sativum (score of 0.214 and 0.017 frequency), Entandrophragma cylindricum (score of 0.214 and 0.017 frequency), Rubia cordifolia (score of 0.214 and 0.017 Frequency) and Scyphocephalium ochocoa (score of 0.214 and frequency 0.017).

Ocimum gratissimum is an aromatic plant used in the treatment of several diseases in many countries and has been reported to contain 8 major groups of different metabolites ²⁶ which may be related to its medicinal properties.

The performance indices were calculated (Table 2) and only plants involved in several respiratory pathologies (in this case, the most cited pathologies) and which were in competition with others were taken into account. 

Table 2: Performance indices of plants directed against respiratory diseases