To our knowledge, this is the first systematic review and meta-analysis on the status of canine leishmaniasis in Morocco. The results presented in this report are based on the meta-analysis of data obtained from a systematic review of scientific work on the prevalence of canine leishmaniasis in Morocco between 1932 and 2021. The majority of the studies were carried out from 1982 onwards and more than half of them came from the central regions of the country. It is within this framework that the present review attempts to assess the status of the canine leishmania reservoir in Morocco. However, it should be noted that although the term canine leishmaniasis refers to animals belonging to the canidae, in Morocco this term is often used to designate leishmaniasis affecting dogs whether it is the bladder or skin form. Therefore, we will use the term "canine leishmaniasis" instead of dog leishmaniasis throughout the discussion of our results.
In Morocco, the dog is considered the main reservoir host of Leishmania and the source of infection because it plays an essential role in maintaining the chain of transmission to humans (Ministry of Health, 2010). The NPCL established in 1997 and revised in 2010 states that control of the severe visceral form of L. infantum leishmaniasis requires control of the canine reservoir and advocates a strategic focus on eliminating this disease by 2030 (Ministry of Health, 2016 ; El-Mouhdi et al., 2020). Unfortunately, there is no documented data on the global estimate of the seropositivity status of the canine reservoir in Morocco. The existence of such information allows policymakers to further focus their control efforts to target at-risk areas where canine reservoir foci are active. Indeed, leishmaniasis in the canine population is a very important indicator to be taken into consideration to prevent the disease in humans.
To date, the status of canine reservoir infection with leishmania is unclear and the overall estimate of leishmaniasis prevalence in dogs is unknown. It is in this perspective that the present review was conducted to know the status of canine leishmaniasis in Morocco and the risk factors associated with the disease to provide officials with an effective reference tool indicating active foci of canine leishmaniasis with high prevalence where control actions should be conducted to prevent the risk of occurrence of visceral leishmaniasis cases in humans.
This work is the result of the synthesis and meta-analysis of the various individual studies carried out on the seroprevalence of canine leishmaniasis in Morocco. Was conducted following precise and predetermined steps (Higgins & Green, 2008). Strict and rigorous criteria were followed in the selection and identification of studies to be included in this work (Deeks et al., 2008).
Specifically, after an exhaustive literature search of published and unpublished studies, 15 studies were eligible for this review. It included studies examining the seroprevalence and risk factors associated with leishmania infection in the canine population in Morocco. These studies underwent a quality control review primarily concerned with assessing the risk of bias of the included studies and was performed using the assessment tool for studies reporting prevalence data (critical-appraisal-tools - Critical Appraisal Tools | Joanna Briggs Institute, 2020). Our results show that the risk of bias was low. Moreover, the majority of the studies were conducted in the 8 administrative regions representing 66.6% of the whole country, which seems fairly representative. This allows us to draw reliable conclusions about the overall prevalence of canine leishmaniasis in the country.
Of all the primary studies collected, 11 studies (Guessous-Idrissi et al., 1997 ; Nejjar et al., 1998; Sahibi et al., 2001; Fellah et al., 2014; Natami et al., 2000; Rami et al., 2005; Nejjar et al., 2000; Dereure et al., 1986; Rami et al., 2003; Boussaa et al., 2014 ; Velu et al., 1932) reported prevalence data. In fact, out of a total of 3900 dogs diagnosed 580 were found positive for leishmania with an apparent prevalence of 14.87%.
The diagnostic methods that were used ranged from simple biochemical tests to molecular tests. The pathogens incriminated in cutaneous and visceral leishmaniasis in dogs ranged from frequently identified strains (L. infantum zymodeme MON-1) in the majority of studies to rare strains (L. tropica MON-102; L. tropica MON-113; L. tropica MON-279 and L. infantum MON-24) identified during sampling of the canine population and being the subject of the short communications. This can be explained, on the one hand, by the predominance of the L. infantum strain in the canine population in Morocco as in the rest of the Mediterranean countries (Organization & Mediterranean, 2017), and on the other hand, by the virulence of the pathogenic strains circulating in the high prevalence provinces insofar as the visceral and cutaneous forms of canine leishmaniasis can be caused by strains belonging to Leishmania infantum (Dereure et al., 1991; Haralambous et al., 2007) and Leishmania tropic (Sahibi et al., 2001; Lemrani et al., 2002; Guessous-Idrissiet al., 1997).
Meta-analysis of all these studies showed that the overall combined prevalence of canine leishmaniasis in Morocco was 17% (95% CI: 0.12–0.22; p < 0.00001). It was very high in the regions bordering the Mediterranean, notably in the provinces of Rabat (42% [95% CI: 0.25–0.59]), Nador (21% [95% CI: 0.10–0.32]) and Al Hoceima (15% [95% CI: 0.01–0.29]). And in the central region of the country, specifically in the provinces of Chichaoua (33% [95% CI: -0.05-0.71]); Sefrou (28% [95% CI: 0.17–0.39]) and Moulay Yacoub (27% [95% CI: 0.10–0.44]). These differences in the distribution of prevalence across Morocco can be attributed, on the one hand, to the specific characteristics of each region, and on the other hand, to the biological characteristics of the dogs in these regions.
On the other hand, a critical analysis of the literature over time showed that the prevalence of canine leishmaniasis in the early years of publication (1932–1951) was estimated at 13% (95% CI [0.03–0.23]; p = 0.01). In this period, the main documented canine surveys were carried out in the provinces located on the Mediterranean coast, namely in the city of El Jadida (at that time called Mazagan) and in the city of Casablanca to ascertain the existence of leishmaniasis in dogs (Velu et al., 1932). The results obtained affirmed that canine leishmaniasis is exceedingly rare, if not non-existent in Morocco (Velu et al., 1932). A decade later, this finding was confirmed by Zottner in 1941 when he published a report of an autochthonous case of symptomatic canine leishmaniasis in Morocco, which he considered to be the 3rd case observed in Morocco after the 1st case which was reported by Jeaume in 1932 in a fox dog born and raised in Tangier and the 2nd case by Flye Ste Marie in a rural dog in Fes (Zottner, 1941). These two dogs were found to be carriers of the Leishmania parasite despite being asymptomatic (Zottner, 1941). At that time, researchers concluded that if leishmaniasis disease exists in the canine species, the percentage of contaminated animals is certainly low and difficult to establish (Velu et al., 1932; Zottner, 1941). Therefore, studies on canine leishmaniasis in Morocco were stopped for the next 30 years. This probably explains the absence of publications between the years 1952 and 1981 and the impossibility of estimating the prevalence in this second period.
However, during the third period from 1982 to 2001, there was a strong return to the study of canine leishmaniasis. The publications in this period represent 47% of the total number of publications. This resurgence can be explained by the signalling of the increase of indigenous cases of infantile visceral leishmaniasis (Kirmse et al., 1987). In fact, this period was also marked by the official launch of the NLCP (Ministry of Health, 1997) and leishmaniasis became a concern for health authorities. In addition, the publications in this period were very rich in terms of the identification of circulating pathogenic strains and the term discovery of indigenous zoonotic cycles in the country. They proved the existence of a zoonotic cycle of canine visceral leishmaniasis caused by L. infantum MON-1 in the southern areas of Morocco (Dereure et al., 1986) and discovered for the first time, in 1991, the presence of canine cutaneous leishmaniasis caused by L. tropica zymodemus MON-113 and zymodemus MON-102 in Azilal and Essaouira provinces (Dereure et al., 1991). Also, for the first time in Morocco, a case of canine visceral leishmaniasis caused by L. tropica was reported by Guessous-Idrissi et al. 1997 in the North of the country (Guessous-Idrissi et al., 1997). The second case was found by Sahibi et al in the locality of Oulde Hsain in the province of Taounate Sahibi et al. 2001(Sahibi et al., 2001). Endemic foci of canine leishmaniasis have been reported in the north and centre of the country and have been found by several researchers (Natami et al., 2000; Sahibi et al., 2001; Nejjar et al., 2000; Guessous-Idrissi et al., 1997; Nejjar et al., 1998). Thus, the results of our meta-analysis revealed that the combined prevalence in this period was found to be increased with a percentage of 15% (95% CI [0.10–0.16]; p < 0.00001).
The fourth period (2002–2021) was characterized by the continued identification of other active foci of canine leishmaniasis in the northern, central and southern regions of the country (Fellah et al., 2014; Rami et al., 2005; Rami et al., 2003; Boussaa et al., 2014). In addition, the main novelties noticed in this period were the publication of the results on the detection of new zymodemus of the pathogens of the disease: the first one was L. tropica MON-279 proved for the first time as the causal agent of the visceral form of canine leishmaniasis in the north (Lemrani et al., 2002) and the second one was L. infantum MON-24 demonstrated as the causal agent of the cutaneous form of canine leishmaniasis in the Pre-Rif region of Morocco (Haralambous et al., 2007). Estimation of the pooled prevalence in this period showed that it was increased to 24% (95% CI [0.10–0.25]; p = 0.0001). In addition, the Ministry of Health announced that it revised the NLCP and published its updated version in 2010 (Ministry of Health, 2010). In this edition, the program has reserved a strategic axis for the control of dogs suspected as the reservoirs of L. infantum in Morocco, while humans remain the only reservoir of L. tropica (Ministry of Health, 2010).
In addition, several epidemiological studies have reported the frequent coexistence of human cases of cutaneous leishmaniasis due to Leishmania tropica and Leishmania infantum in temperate zones, especially in the center and north, whereas this coexistence has not been noticed with cases due to L. major, whose reservoir is the rodent "Meriones Shawi", which is present in the South of Morocco. And no explanation has been found to understand this association. Referring to the results of this study, we can say that the simultaneous occurrence of skin lesions due to L. infantum and L. tropica in the Moroccan population in humid areas is justified by the presence of the dog which has been shown to be the reservoir of both species. In addition, the presence of the sand fly vector is very common in the Moroccan territory; it is popularly known by the name of "Chniwla" and is often confused with the mosquito (El-Mouhdi, Chahlaoui, & Fekhaoui, 2020). Unfortunately, the use of means of protection and prevention against its health risks by citizens are not adapted (El-Mouhdi et al., 2020), (El-Mouhdi et al., 2021).
Certainly, human leishmaniasis is a public health problem in Morocco, the bladder form is fatal in the absence of treatment and the cutaneous form due to L. tropica is endemic in several areas of the country, it presented alone 43% of all cases reported (El-Mouhdi et al., 2020). At our level, it is suggested that the control strategy against the canine reservoir of leishmaniasis in Morocco should be renewed taking into consideration this new data. In this way, the effective control of the canine reservoir will reduce the human cases of leishmaniasis due to L. infantum and L. tropica. The culling of stray and symptomatic dogs as the only strategy to prevent human risk is outdated (Ministry of Health, 2010). A holistic approach must be adapted in the control of leishmaniasis and particular emphasis must be placed on dog population management adapted to the country context if Morocco is to eliminate mortality from visceral leishmaniasis and achieve Sustainable Development Goals by 2030 (El-Mouhdi et al., 2019).
Therefore, it emerges from this spatiotemporal meta-analysis of the combined prevalence of canine leishmaniasis in Morocco at the regional and provincial level during these 90 years (1932–2021) of study that, on the one hand, the high prevalence rates that were reported during the first period in the provinces bordering the Mediterranean side persisted during all periods, On the other hand, high prevalence rates in the central regions appeared from the third period and continued in the fourth period where high prevalences were recorded in the southern regions. This means that, over time, canine leishmaniasis spread from the north to the center and then to the south of the country by gaining new foci. This can be explained by the wandering lifestyle of stray dogs carrying the infection through hamlets and villages that forces them to move in search of food and shelter (Kholoud et al., 2020). However, it can also be explained by exposure to other factors that may be directly related to the dog (intrinsic factors) or related to the external environment (extrinsic factors).
For the intrinsic factors which include age, sex, breed and clinical status, our results show that seropositivity increased with the age of the dog, it was higher in adult dogs older than 4 years (64% 95% CI: -0.15-1.43]) compared to the youngest ones of less than 2 years (30% (95% CI [-0.09-0.68]; p = 0.13). This may be explained by the long latency period of the disease in the dog after infection (Oliva et al., 2006), or by the increased contact with the disease vector sand fly in public dumps and household waste while foraging.
Furthermore, the risk of leishmania was twice as high in healthy dogs with asymptomatic to symptomatic clinical status (RR = 2.08 [95% CI: 1.15–3.76]; p = 0.02). In fact, the prevalence in asymptomatic dogs was 9% (95% CI [0.06–0.13]; p < 0.00001) and in symptomatic dogs 5% (95% CI [0.02–0.09]; p = 0.003). This can be explained; on the one hand, by the culling of clinically suspected stray dogs under the NLCP (Ministry of Health, 2010), on the other hand, can be explained by the attractiveness of asymptomatic dogs to sandflies (Belo et al., 2013; Shokri et al., 2017). At our level, it is assumed that the very difficult lifestyle of Moroccan dogs reflects the clinically suspect aspect which in reality lived in lack and abuse. In addition, recent studies conducted among Moroccan citizens and health professionals have shown that dogs are poorly known as reservoirs of leishmaniasis (El-Mouhdi, Fekhaoui, et al., 2020; El-Mouhdi, Chahlaoui, & Fekhaoui, 2020)].
However, the sex of the dog was not found to be associated with leishmaniasis infection (RR = 1.14 [95% CI: 0.75–1.73]). These results confirm those found in the primary results (Rami et al., 2003; Fellah et al., 2014) and those found by Belo and colleagues (2013) in Brazil (Belo et al., 2013).
Regarding extrinsic factors including altitude, living environment, lifestyle and health status of the dog, the results of our analysis showed that canine leishmaniasis in Morocco was present in all altitudes but with a high prevalence in altitudes above 1000m (26% [95% CI: -0.2–0.53]). This can be explained by the biological activity of the vectors involved in the transmission cycle of L. infantum, notably P. perniciosus, P. ariasi and P. longicuspis, which are very active at high altitudes (Boussaa et al. 2008). Indeed, Boussaa et al (2008) showed that Larroussius species, P. perniciosus and P. ariasi are very frequent in the altitudes 1000m-1400m and P. longicuspis was very active in the altitudes of 800m to 1000m (Boussaa et al., 2008).
Comparison of the combined prevalence according to the living environment of the dog revealed that it was higher in rural areas (18% [95% CI: 0.14–0.23]; p < 0.00001) compared to urban areas (15% [95% CI: 0.01–0.29]; p = 0.04). This difference can be explained by the abundance of the canine population in rural areas than in urban areas because of their usefulness to farmers. In fact, each rural Moroccan family owns an average of 2 to 4 dogs, which are used to guard livestock (Nejjar et al., 1998). But also, the prevalence was high in urban areas where dogs found their favorable environment in public dumps and garbage dumps (Kholoud et al., 2020).
Thus, for the dog's lifestyle, our results revealed that 75.8% of the dogs lived in chains, 2% of the dogs were strays and 22.2% were semi-strays. Similarly, 8.1% were found to be under veterinary care, while 91.9% were found to be without veterinary care. Unfortunately, it was not possible to estimate the pooled prevalence of these two categories of dogs or to establish a risk ratio because no studies reported seropositivity data in relation to these two variables.
In sum, dogs have no predators in these two environments, other than being killed by humans, they have a short and rapid reproductive cycle, with an average of five to six pups, the number of dogs increases rapidly as its food supply is assured (Pal, 2003), Therefore, the likelihood of the risk of spreading Leishmania will be more increased. This reinforces the relevance of designing a dog population management strategy in Morocco based on the promotion of the dog lifestyle in collaboration with government authorities and community and veterinary leaders for the protection of these animals through education and awareness actions, especially to dog owners. Thus, the control of canine leishmaniasis requires courageous actions that allow dog owners to proceed to (a) registration of their dogs, (b) implementation of regulations on breeding, veterinary monitoring and sale of dogs, (c) sterilization procedures, (d) application of protective collars against insect bites, and (e) establishment of direct legislation to dog owners (World Organisation for Animal Health, 2021).