Assessment of the Clinical, Serological and Parasitological Aspects of Onchocercal Skin Disease, 20 Years of Community Directed Treatment with Ivermectin (CDTI) in the Ruvuma, Southwestern Tanzania

Background: Onchocerciasis is a chronic disease caused by filarial worm, maintained in the communities through the black flies that breed in rapid fast flowing rivers. The disease triggers enormous sufferings and compromise community and individual socio-economic opportunities. Approximately 37 million people are afflicted by onchocerciasis and 46,000 new cases of blindness are reported each year in the hyper-mesoendemic communities. Study objective was assessing interruption of transmission after over 20 years of mass drug administration in the area. Methods: In this descriptive study design, clinical signs, symptoms and skin snip results were the parameters used to diagnose Onchocercal skin disease (OSD) in hyper and hypo/non-endemic communities. Quantitative PCR was used to confirm the diagnosis and determine the number of onchocerca volvulus (o.v.) genomes present in the skin specimens of onchocerciasis cases and non-infected cases. Results: A total of 106 individuals participated in this study, 59.4% (63/106) were males. The median age was 49.5 years with an inter-quantile range of 36 to 62 years and the mean weight was 55.7 kg with a 95% CI of 53.8-56.7 kg. Microfilaridermia prevalence in the hyper and hypo / non endemic communities was 48.1% (51/106) and 1.0% (2/228) respectively with geometric mean intensity GMI of 2.8mff/mg skin with 95% CI of 2.5-3.1. The prevalence of troublesome itching was 9.6% (49/513) the hyper and hypo/non endemic communities respectively. Chronic papular onchodermatitis (CPOD) prevalence in the hyper-endemic villages was 24.5% (26/106) presented by itching along with scratch marks. An association between CPOD and microfilaridermia was observed (r=-0.27; p=0.047) while in the hypo and non-endemic communities the most frequent skin lesion observed was scabies and a red scaly skin rash. The amounts of O.V. DNA detected in the specimen varied greatly. Twelve participants had data on O.V. DNA and expressed higher levels of O.V. DNA (r2 = 0.25). Conclusion: These findings have shown clearly that, transmission has not been interrupted in the entire focus. However, in areas considered non endemic in the previous surveys today transmission is ongoing.


Introduction
Onchocerciasis is a parasitic disease caused by Onchocerca volvulus, a filarial nematode transmitted by black flies (Simulium sp.) The clinical expression of the disease is characterized by dermatologic and ocular manifestations namely; itching, pruritis, dermatitis, depigmentation, pre-matured skin atrophy, discoloration, and ocular lesions in the anterior and posterior segments of the eye. Over time, accumulated ocular damage can result in visual loss and blindness, the disease is ranked as the fourth leading infectious cause of preventable blindness [1]. It is estimated that, 37 million people are infected [2] with 46,000 annually new cases of blindness (http://www.apoc.bf/). The disease is endemic in sub-Saharan Africa and phylogenetdesowitzically proved to have relationship between African Old World and America New world (https://graduadeway.com/onchocerciasis-in-latin-America/. It is for this reason that, parasite onchocerca volvulus is known to be imported from the West Africa to Americas through the slave trade [3] and spread further through migration [3]. Although the disease was introduced from Africa, it was first described in 1915 by Rodolfo in Guatemala [4]. The ocular and dermatological morbidities together with the abandoned of individuals from the very fertile land in West Africa triggered the international organizations such as WHO to plan for control programme which was named Onchocerca control programme (OCP) in some 11 countries of West Africa. This was the area where the savannah strain of parasite causing blindness [5,6] are residing. On the other hand, another strain, the forest type non blinding was responsible for the severe skin disease, commonly found in Central & East Africa [7,8].
The introduction of ivermectin a veterinary medicine into the management of filarial diseases in humans was a breakthrough during the 1987. This was also the time the drug was registered and licensed as a drug for treating onchocerciasis and lymphatic filariasis. Since then, control measures have been intensified in some endemic areas in the Americas and Sub-Saharan Africa.
However, the use of ivermectin as a control tool has had an impact on the disease prevalence leading to increased reports of an increasing successful story on interrupting transmission in the endemic foci of the Americas, West and East Africa [9][10][11][12][13]. On the other hand, this recent successful control activity was attributed to annual/semi-annual rigorous and sustained community directed treatment with ivermectin (CDTI). Since ivermectin is only lethal to the larval stage (microfilariae) but not the adult parasite, prolonged treatment rounds at semi-annual might halt transmission in those endemic areas mostly the hotspots. Moreover, the proportion of animal-filariae in the vector has direct and indirect consequences for parasite transmission to humans [14,15] causing an important factor to understand the epidemiology of the disease. Additionally, filariae closely-related to nematode onchorca volvulus might repopulate the human host [16] contributing to a potential risk of infection or could transfer genes to O. volvulus which could negatively alter effectiveness of ivermectin [17,18]. After the closure of the OCP control programme, which were targeting the simulium vectors using insecticides, a need to proliferate continuation of the control activities was crucial hence adopting a new strategy the chemotherapy [19][20][21][22]. Around 1987 a veterinary drug ivermectin was licensed to treat human helminthic disease and therefore in 1995 an alternative programme was formed, the African Programme for Onchocerciasis Control (APOC), to take up the control activities using chemotherapy this time, the ivermectin which was supported by Mectzan as donation for the entire period as required until the disease is eliminated in 20 countries including Tanzania. In Tanzania, prevalence rates of onchocerciasis in endemic areas range widely, from 3.5% to 63.6% in the known foci [23,24]. The epidemiology of the disease has also changed in recent years, possibly due to local environmental and global changes in climate and human populations as well as parasite and vector dynamics and heterogeneity in the human host response [25]. It could also reflect natural attrition of mff, which secrete Wolbachia bacterial endosymbiont products into the general circulation, inducing immune responses and inflammatory cytokines, resulting into pathologies in different organs [26,27] including the brain possibly provoking the different forms of epileptic seizures due to leiomodin 1 in a repeatedly manner [28,29]. In endemic areas, 40-50% of adults are symptomatic, with devastating socioeconomic consequences whereby entire villages are abandoned. The effectiveness of the sole treatment, ivermectin, is declining and there is increasing resistance to this drug [30][31][32].
There is therefore an urgent need to understand the pathogenesis and current epidemiological status of the disease in those endemic foci as a basis for developing new control and treatment strategies towards elimination of onchocerciasis.
In Tanzania, onchocerciasis is prevalent in 15 districts which lie within the tropical rain forest. In these areas, the epidemiological profile has been experiencing environmental changes in favor of the parasite and vector creating an increased threat to the human population in the area. According to previous endemicity data in those same foci it appears that, transmission is still on ongoing. Those foci are linked by the Eastern Arc Mountain chain of Block Mountains which stretches from northeast Tanzania to Northern Malawi and from the Tanga region to the Ruvuma and south-western Mbeya regions in Tanzania [33,34]. In 1993 WHO estimated 650,000 individuals were infected with onchocerciasis in Tanzania but there is a wide variation in the disease prevalence in the different disease foci [35,25,36,23].

Study Area
Songea is the largest single onchocerciasis focus within Ruvuma were selected according to their endemicity levels/status, being hyper-endemic, meso-endemic, hypo-endemic or non-endemic, on the basis of endemicity levels from historical data [23,36]. Study investigators provided an explanation and the project aims to district authorities and community leaders thereafter meetings with community health leaders and administrators were conducted to sensitize the study population. The discussion focused on the current status of OSD after ivermectin distribution in those areas.
After such meetings, permission to carry out the study at each local setting was granted. Thereafter, local leaders asked community members willing to participate in the study to visit the local health facility (village dispensary/health centre) where written and oral informed consent was obtained. The next day those who consented came back for a physical examination and a blood specimen and skin snips were collected together with dietary intake information. Visual acuity of each individual was also investigated by an ophthalmologist using Snellen's letter chart for those who could read or Sjogren's hand test for those who were illiterate, at a distance of 6 meters from the individual. Similarly, the anterior chamber and fundus of each eye were examined, using a slit lamp directly or indirectly by using an ophthalmoscope. Both eyes of each individual were checked for fluffy opacities in the cornea, sclerosing keratitis, and the presence of microfilariae (mff), after an individual sat down inclined for two minutes.
Parasitological Examination: Skin snipping using corneoscleral biopsy punch was performed on each study participant taking skin snips from the right and left iliac crest, pelvic girdle, right and left buttocks. Before snipping was conducted, the skin was disinfected with 70% alcohol, and allowed to dry prior to

Results
Eleven communities in four different districts of the Ruvuma region were examined in order to identify suitable individuals for the study (Table 1) (Table 2). A high proportion (67.6%) of the study participants had acquired primary or secondary education, while 32% did not attend any formal school and the primary occupation of over 90% of the participants were peasant.

Onchocercal skin lesions and microfilaradermia observed in the study population
The vast majority of these onchocercal skin lesions were observed in study participants from endemic villages; 49% with CPOD, 35.3% with APOD or Atrophy, 27.5% with DPM, and 90.2% suffered from dermal itching (Table 3) Table 4 shows the anatomical location where mff-positivity were detected, of those 19 and 26 presented APOD and CPOD respectively. APOD was the common skin lesion observed on the arms, abdomen, shoulder, back, buttocks and legs. However, lesions on the head, neck, chest, groin, and perineum were much less common, observed in less than 15.8% of individuals. Those individuals with COPD, were commonly observed on the arms, abdomen, back, buttocks and legs with proportions ranging from 73.1% to 100%. Whereas lesions on the head, neck, chest, shoulder, groin, and perineum were less common, each observed in less than 38.5% of the individuals.
The mean age of APOD in the endemic villages was lower as compared to CPOD, Atrophy and DPM; on the other hand, the prevalence of those conditions was also high in the endemic villages than in the hypo-endemic/non-endemic villages. However, those individuals complaining of itching did also present onchodermatitis.
The mean mff total count (summed over 6 body sites) was 26.6 (median 15, min.1.0, max. 191.0), with a highly left-skewed distribution (data not shown). The mean itch score was higher among the individuals from endemic communities than among the individuals from the non-endemic/hypo-endemic communities (max. possible: 13) was 5.9 (min.0, max. 10). However, there was no correlation between mean mff total count and mean itch score (r=0.08).
Itching was observed as scratch mark in the following body regions namely; head and neck 1.9% ( 2/106), anterior chest 8.5%

Other Skin Lesions Observed with Association with
Onchocercal Skin Disease: Individuals with impaired visual acute according to the Snellen test were 4.7% (5/106) these were also mff positive individuals.
Palpable Nodules: Palpable onchocerca nodules were observed in 5.0% (5/106) of the study participants. Four were males and one female. Nodules were localized at the inguinal area while 3 were observed at the femoral area.

Clinical Disease, cellular and parasitological
To assess whether treatments using CDTI and other ivermectin distribution strategies had effect on onchoceca volvulus in the endemic villages during the 20 years and beyond. The aim was to compare two similar setting with historical background data on transmission levels (meso-endemicity Vs hypo/non-endemicity) those studies, [23,36]. Therefore, clinical and parasitological methods were used to stratify the study participants into cases 1. The initial infections levels pre-treatments were high in the two settings than historical data from research background 2. Could also be the treatment coverage in the area was low than the WHO recommended levels [40] raises the concern that, the parasite populations particularly their Surprisingly in the hypo/non-endemic villages clinical disease (oncho-dermatitis) was not a common feature, despite itching and scratching was a frequent reported feature in those communities.
Although itching and reactive dermal lesions were common in all studied age groups in the endemic villages, they were generally present among the 20-40 age group which is the economically productive populations (Figure 2) involved in coffee and maize farming. This is an important aspect during the process of MDA since these peasants moved from their households to farms during the farming period and remained there until harvest period hence missing treatment. Therefore, extra effort is crucial to make sure such peasants are also covered during treatment with ivermectin through the CDTI strategy. In these endemic areas, the disease has features of rain forest, parasite strain whereby excruciating itching has been the main cause of morbidity [47] whereas visual impairment is uncommon. Elsewhere, such symptoms have been conflicting particularly adolescent females and women affecting marriage prospects [48], education, self-esteem [49], psycho-social alterations and neurological seizures [50,51]. Similarly reduced working capability and performance hence affecting individual socio-economic aspects [52]. Additionally, OSD-itching has been shown to significantly shorten the period of women to breast feed their neonates because of fatigue secondary to incessant itching [48].

Why Transmission has Not been Interrupted in the Studied Area
Why transmission has not been interrupted in this focus despite mass drug administration (MDA) has been implemented for over 15 years which is a long-term treatment using annual single drug strategy according to Tekle et al. [12] 2012) elsewhere [12]. Some possible factors which might contribute to this are discussed 1. The design which was initially planned as case control but at the point of analysis we found that even in the areas considered non-endemic according to previous historical data, [23][24][25] a high infection rates was observed through PCR.
2. Some individuals were not able to be examined because, the mountainous topography of the area, hindered some of the said

Conclusion/Interpretation
These results have shown clearly that within the focus, transmission has not been interrupted in the entire focus although exists signs of some villages having low infection and others appears that infection has stopped. However, in areas considered non endemic in the previous surveys today transmission is ongoing.