ANTITRYPANOSOMAL EFFECT OF CRUDE SCORPION VENOM EXTRACT IN TRYPANOSOMA EVANSI INFECTED SWISS ALBINO RATS

ABSTRACT

Despite the control measures against trypanosomiasis over the past few decades, the disease still contributes to the current economic losses and socio-political crises in the sub-Saharan Africa.   The   recent   interest   of   chemotherapists   in   aggressive   search   for   novel antitrypanosomal  drug  agents  informed  this  current  investigation  to  elucidate  the  acute toxicity and antitrypanosomal efficacy of crude scorpion venom in  Trypanosoma evansi infected rats. Eighty (80) medium sized scorpions, brownish in colour with robust metasoma ending in telson were collected from their habitat in Minna metropolis. Venom was collected by electric stimulation of each scorpion telson. Acute toxicity of the venom was established through oral injection of the scorpion venom using graded concentrations (10, 20 and 30 mg/kg body weight) with saline extract of crude venom. The antitrypanosomal bioassay of the venom was performed against established infection in Trypanosoma evansi infected rats. Group 1 was set up as negative control of 0.2ml normal saline /kg/body weight, group 2 as 5mg chloroquine /kg/body weight and group 3 to 5 as 10, 20 and 30 mg/kg/body weight of the scorpion venom. Acute toxicity showed an LD50  extrapolated to be 44.72 mg/kg body weight. Antitrypanosomal bioassay results showed scorpion venom significantly (P˂0.05) reduced the level of parasitemia of the infected rats, with peak activity recorded on the last day of observation, a pattern distinctly different from the positive control and total parasite clearance was recorded on the 5th day in the group treated with 20 and 30 mg/kg body weight venom concentration having 0.00 and  0.00±0. Treatment of infected rats  with scorpion venom extract significantly (P˂0.05) ameliorated loss in some body enzymes tested. The crude venom extract also promoted fall in Packed Cell Volume of T. evansi infected rats, promoted body weight loss for the infected untreated group   having 71.23±1 against the initial weight of 123.45±1 and elongated the survival time of T. evansi infected rats. Treatment of the infected rats with scorpion venom at 20 and 30 mg/kg body weight significantly restored the liver and spleen to body weight ratio to a level comparable with the normal rats. Findings from this study suggest that scorpion venom posses a potent and promising source of antitrypanosomal agent.

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background to the Study

Human  African  Trypanosomiasis  (HAT) is  a neglected tropical  disease that  occurs in  sub- Saharan Africa, within the distributional limits of tse-tse fly vector. Two forms of the disease exist (Feyera et al., 2011; Mulaw et al., 2011). The slow-progressing form, caused by Trypanosoma brucei gambiense, is found in western and central Africa. The fast progressing form, caused by Trypanosoma brucei rhodesiense, is found in Eastern and Southern Africa (Simarro et al., 2010). A person can be infected for months or even years without major signs or symptoms of the disease, when more evident symptoms emerges the patient is often already in an advanced disease stage where the central nervous system would have been affected (WHO, 2018). It is classified as neglected due to the limited amount of research and control funding allocated to it compared with malaria, HIV and tuberculosis.

African  Animal  Trypanosomiasis  also  called  “nagana”  a  Zulu  word  for  powerless/useless parasitic disease caused by T. b. brucei, T. b. rhodesiense, T. congolense and T. simiae in pigs (Loker & Hofkin, 2015). Trypanosoma evansi causes ‘surra’ a disease in camel, rats, horses and buffalo (Reid, 2002). Trypanosome that causes serious economic losses in livestock from anaemia, loss of condition and effects on reproduction, losses in cattle are especially prominent. Animals other than livestock including dogs can be affected. Untreated cases can be fatal, and the mortality rate is high in some outbreak (Auty et al., 2015).

Sleeping sickness and nagana have a great economic impact in Africa because it affects the settlement patterns of people including land use and farming (National Tsetse and Trypanosomiasis Investigation and Control Centre, 2016).

World Health Organization (WHO) in 2010 attributed trypanosomiasis as the deadliest disease in the world. The treatment of this menace has since been a burden because of the adverse drug reactions that most drugs present when given to the patients (Ugoji et al., 2014).

The immune response of animals could be unable to eliminate trypanosomes completely, and the animals could become inapparent carriers. These inapparent infections can be reactivated if the animal is stressed, transplacental transmission can also occur (Center for Food Security and Public Health, 2017).

Human African Trypanosomiasis (HAT) is still reported from more than twenty (20) countries in Africa where it causes serious morbidity among the affected rural populations, and it continues to pose the threat of severe epidemics (Franco et al., 2014).

The highest effect of trypanosomiasis however has been its impact over land use systems that have been adopted in the Luangwa valley in Zambia. In-depth knowledge is required to identify specific circumstances where win-win trade off can be achieved between the conservation of biodiversity and the reduction of the disease in the human population (Anderson et al., 2015).

In Nigeria, as in some other western African countries, Trypanosoma brucei gambiense is the etiology of sleeping sickness or Human African Trypanosomiasis (Akish et al., 2016).

The second stage called meningoencephalitic of the infection is usually severe, affecting the cerebrospinal unlike the first stage hemolymphatic stage which is usually less severe fluids of humans clinical presentations include dullness, intermittent somnolence and apparent confusion.

Also, intention tremor in all limbs and myoclinic jerks are often seen (Onyebiguwe et al., 2010; Akish et al., 2017).

Trypanosomes causing Human African Trypanosomiasis are classically transmitted by the bite of blood sucking tsetse flies (Diptera, genus glossina). T. b. gambiense can also be transmitted congenitally (Rochas et al., 2004; Lindner & Priotto 2010; Lestrade-Carluer et al., 2016).

Ever since the creation of mankind, humans have been battling with the challenge of arthropods such as flies, spider, scorpions etc. Scorpions are predatory arachnids and members of the order Scorpiones, they have long been known for their painful, venomous, fatal sting and for their specific morphology (Dehghani, 2015). Identifying various species of scorpion and their biological, nutritional and ecological features has become a common practice in zoology and is used in scientific research in different field such as genetics, physiology, ecology and medicines (Dehghani, 2008; Dehghani et al., 2016).

Scorpions are the most primitive venomous, arachnids of the order Scorpiones (Ortiz et al., 2015; Zhang et al., 2015). They belong to the class Arachnida of phylum Arthropoda (Zhang et al., 2015), have eight legs and are easily recognized by the pair of grasping pedipalps and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger (Ortiz et al., 2015). Scorpions range in size from 9mm/0.3 in (Typhlochactas mitelli), 23cm/9 in. (Heterometrus swammerdami).

Venom produced by scorpion has attracted researchers because of its toxic properties which has help to modify our understanding about various biological phenomenon, it is a combination of various bioactive compounds which are been used in investigatory study of Pharmaceutical research (Oukkache et al., 2008).  It possesses immunosuppressive, cytotoxic, apoptogenic and antiproliferative effects (Zargan et al., 2011).

Scorpion venom is a rich source of biomolecules, which can cause uneasy physiological activity on envenomation and may also have therapeutic potential (Ding et al., 2014). Despite of its numerous negative effects, it contains many biologically active components which are being used for the development of drugs in Pharmaceutical industries (Andreotti et al., 2010; AbdulRahman et al., 2016; Zhang & Zhang 2016).

Being the oldest venomous species, scorpion had been extensively studied for venom production (AbdulRahman et al., 2016). Venom differs in composition from species to species and their effectiveness varies due to the changes in their toxins associated with environmental and genetic variations such as climate and diet (Rodriguez-Ravelo et al., 2013; Pucca et al., 2014).

The current chemotherapy of HAT relies on only six drugs (Suramin, Pentamidine, Melarsoprol, Eflorinithine,  Arsobal  and  Mel  B), five of which  were developed more than 30  years ago (Shiferaw et al., 2015). Others such as Homidium, Isometamidium and Diminazene aceturate are used in animal infections. Each of these drugs has one or more of these challenges: expensive, not available to the populace that are greatly affected, highly toxic and need trained personnel for its administration. The continued use of the same trypanocides for years has resulted in drug resistance that has been largely responsible for the current chemotherapeutic failures (Geerts et al., 2010; Shiferaw et al., 2015). The poor prospect for a vaccine due to antigenic variation of the parasite is further compounded by unwillingness of the Pharmaceutical industry to develop new compounds because of uncertain and unprofitable, market or perhaps the localized nature of the disease.

1.2        Statement of the Research Problem

In  spite  of  the  efforts  in  the  past  few  decades  for  the  control  and  management  of trypanosomiasis, the infection still pose great threat causing 50,000 to 500,000 mortality yearly. Being a neglected tropical disease, trypanosomiasis has added to heavy economic losses and socio-geopolitical crises, especially in the sub-Saharan Africa. Besides, efforts to develop novel vaccine  against  the  disease  still  remained  in  the  embryo.  Hence,  the  disease  still  exerts devastating effect on life stock and human health. The exploitation of plant based remedy is facing challenges of ineffectiveness and parasite resistance problem.

1.3         Justification for the Study

The problem facing the effectiveness of the available antitrypanosomal drugs including their cost implication, unavailability to the populace, high toxicity and also lack of expertise for the administration call for need for a better alternative. Additionally, the current antitrypanosomal drugs have developed resistance which calls for the need to search for better alternatives. This problem has been earlier attributed to the main source of the drugs, chiefly plant. Therefore there is need to explore other natural product for their possible potentials against such disease.

1.4        Aim and Objectives of the Study

This study aimed at evaluating the antitrypanosomal efficacy of scorpion venom extract on

Trypanosoma evansi infected Albino Rat. Objectives of the study were to:

i          Determine the acute oral (LD50) toxicity of the venom on Trypanosoma evansi infected Albino Rat.

ii          Determine the effect of scorpion venom extract in Trypanosoma evansi infected rats.

iii         Assess the effect of scorpion venom extract on the body weight and haematological parameters of infected rats.

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