Prevalence and laboratory analysis of malaria and dengue co-infection: a systematic review and meta-analysis

A clear understanding of the epidemiology of malaria and dengue co-infection is essential for informed decisions on appropriate control strategies for both malaria and dengue. In this systematic review and meta-analysis, prevalence/incidence of malaria and dengue infection was related to differences in parasite density, hemoglobin, hematocrit, platelet count, and liver enzymes; AST and ALT among patients were synthesized. All published articles available in PubMed and Web of Sciences (ISI) before October 21, 2017 were searched. We found thirteen cross-sectional and two retrospective studies eligible to be included in the systematic review and meta-analysis. A summarized analysis of the study findings showed that dengue and malaria co-infection was associated with decreased odds of malaria infection, malaria parasitemia, AST, and ALT levels when compared to malaria mono-infection. However, malaria and dengue co-infection was associated with increased odds of platelet and hemoglobin levels when compared to malaria mono-infection.

Malaria and dengue are common in tropical and sub-tropical areas of the world, causing a high rate of morbidity and mortality especially among children [1, 2]. In 2015, about 212 million people were infected with malaria and 429,000 were estimated to have died globally due to malaria infection [1]. Additionally, more than 390 million people required preventive treatment for dengue and close to 96 million manifested clinical symptoms associated with severe dengue annually [2]. Plasmodium sp. can infect humans and manifest a wide range of signs and symptoms ranging from asymptomatic malaria to severe malaria [3]. Cerebral malaria, hypoglycemia, pulmonary edema, bleeding, acidosis, severe anemia, and acute renal failure were the major complications of severe malaria, which may result in death if no prompt or effective treatments are administered [3]. However, people living in endemic areas of malaria usually show asymptomatic or some non-specific symptoms such as fever, fatigue, chills, and malaise [4]. In the endemic areas of P. falciparum malaria, children up to 5 years of age had more common cases than older children and adults. This might be due to older children and adults receiving partial immunity from the infection [4, 5]. As mosquitoes are usually present in a tropical country, the co-infection of both malaria and dengue is evident and can cause acute febrile illness among patients. Atypical lymphocytosis, hemoconcentration, and thrombocytopenia are specific markers of dengue infection, which help differentiate the diagnosis of dengue infection from malaria infection [6‐8].

In the present systematic review of 13 studies based on 12,546 patients infected with malaria and/or dengue, a summary meta-analysis of these 13 studies confirmed decreased odds of co-infected patients as compared to those uninfected with dengue. The finding of a higher prevalence of Plasmodium co-infection with dengue could be due to both diseases sharing the same endemic regions [14]. In those areas (especially in rural, semi-urban, and urban areas), the vector Anopheles and Aedes are present throughout the year. Geographical overlap of both diseases exists for the 3.2 and 3.9 billion people who live in an endemic area for malaria and dengue, respectively [30, 31]. Therefore, the co-infection of both agents in a patient could not be ignored by physicians [26]. The co-infection of malaria and dengue had been reported in the Brazilian Amazon, Nigeria, India, French Guiana, and Tanzania [14, 18, 20, 21, 26, 32]. Infection by these two pathogens may share similar and non-specific clinical signs and symptoms – such as fever, headache, body ache, and fatigue – which may result in the difficulty of identifying one pathogen from the other [33]. A study indicated that the prevalence of co-infection was estimated among hospitalized patients but not in the community [14]. Another study in French Guiana reported that co-infection was due to the high rate of the population’s mobility to malaria endemic areas [20]. One study reported that co-infection frequency was higher especially during September to November [23]. Moreover, another study reported on an asymptomatic malaria infection with a low parasitemia course co-infection in an individual patient [34].

In regard to the immunity of individual patients, a previous study showed that co-infection has been associated with a strong activation of acute phase response, such as Interleukin 6 (IL-6), Tumor necrosis factor-α (TNF-α), and IL1-β and also Th1 cytokines (IFN-γ and IL-12). However, the lower levels of inflammation in the co-infected group were similar to DENV mono-infected subjects [33]. A co-infection exhibited positive TNF, IL-6, Interferon gamma (IFN-γ), IL-7, C-C Motif Chemokine Ligand 4 (CCL4), and IL-10 which was not observed in malaria mono-infection [15]. The co-infection may be caused by the DENV infection reactivating the hypnozoites of P. vivax in the liver, which were asymptomatic for months or years [33]. Previous studies that involved P. falciparum co-infection have reported fatalities [8, 35‐38]. However, the frequency of severe clinical symptoms occurs in P. vivax co-infection [14, 22]. Those severe clinical symptoms may be caused by the activation of acute phase response including IL-6, TNF-α, IL1-β, IFN-γ, and IL-12 [33]. A previous study also showed that co-infection resulted in similar days of fever as compared to single malaria infection, which should therefore raise the suspicion of malaria co-infection [14].

The results from our meta-analysis found that co-infected patients exhibited lower malaria parasitemia than those with malaria single infection. This was in accordance with a previous study in French Guiana [22]. A previous study indicated that low parasitemia is a good predictive marker for less severe symptoms in co-infected patients [24]. The good outcome was because the concurrence of dengue and malaria led to patients seeking out medical treatment earlier (2.2 ± 0.4 days) than those with single malaria infection (5.5 ± 0.9 days), resulting in early diagnosis and treatment with antimalarial drugs [7, 36]. This was the frequency found in P. vivax co-infection [39‐41].

Several studies reported on co-infection cases with severe anemia single malaria infection [14, 16, 22, 42]. Based on this meta-analysis, the hemoglobin level of co-infected patients were significantly higher than those with malaria single infection. This was in contrast to previous studies that indicated low hemoglobin in patients with co-infection [16, 42]. Malaria infection causes destruction of red blood cells followed by hemolysis and anemia [43]. Considering the clinical outcome, co-infection resulted in a lower rate of jaundice than those with dengue single infection [16].

Hematocrit is a marker used to diagnose dengue infection. Severe dengue results in hemoconcentration (the basal hematocrit > 20%), which is the result of increased vascular permeability and plasma leakage in endothelial [44]. Several studies reported no significant change in hematocrit among patients with co-infection when compared to those with malaria single infection [14‐16, 19]. For malaria infection cases, low hematocrit was due to anemia, a common complication in both P. falciparum and P. vivax malaria [45]. However, this meta-analysis showed no significant odds in hematocrit level among those two groups of patients.

This meta-analysis found that co-infected patients had higher odds of platelet count as compared to malaria infected patients. This indicated that co-infected patients had a higher platelet level than malaria infected patients. Some studies indicated that co-infected patients also exhibited lower platelet count or thrombocytopenia than those with malaria single infection [15, 19, 22]. In regard to this meta-analysis, a significantly lower platelet level among co-infected patients was found in two studies [15, 19]. However, two other studies reported that malaria single infection exhibited thrombocytopenia more frequently than co-infection [14, 24]. For the clinical outcome of thrombocytopenia, co-infection had a higher chance of bleeding when compared to malaria single infection (OR 12.5, 95% CI: 4.7–33.3, P value = 0.001) [14].

AST is found in highest concentrations in the heart and also found in the liver, whereas ALT is found mainly in the liver [46]. Elevated AST and ALT can be seen in any type of liver cell injury [47]. Currently, the difference between liver enzymes (AST and ALT) and the clinical outcome of co-infection and malaria single infection is not well established. This meta-analysis found significantly lower levels of AST and ALT in co-infection when compared to malaria single infection. This indicated less liver injuries in the co-infected group. Liver injury was prominent in dengue single infection but not in malaria infection. A previous study showed that liver injuries and bleeding can lead to fulminant liver failure in dengue infection [48]. However, previous studies reported that hepatomegaly was very frequent in the co-infected group [14, 19]. Moreover, higher AST and ALT levels were associated with jaundice and hepatomegaly [14, 19]. Nevertheless, a report in French Guiana showed no differences in AST/ALT and parasitemia levels between co-infection and malaria single infection [22].

In terms of mortality, co-infection can lead to an increased mortality rate when compared to malaria single infection (6.3% compared to 5.5%) [19]. However, a study by Mohapatra et al. found a lower rate of mortality in co-infection as compared to malaria single infection [24]. The clinical outcome of co-infection was more similar to dengue single infection than malaria single infection. Therefore, the physician must be aware of co-infections in malaria cases with inadequate treatment response as well as screening for malaria parasite in patients with dengue [24].

The interaction of dengue and malaria in co-infections is unknown but the multiple infections may lead to a failure in treatment [49]. The underlying conditions in co-infections are rhabdomyolysis and sickle cell disease, which result from TNF-α and RBC sequestration in skeletal muscle, increased blood viscosity, and toxins from the parasite together with lactic acidosis [35]. A study found that co-infection had a predominance of Immunoglobulin M (IgM) antibody [22]. Another study indicated that malaria infection might be triggered by dengue infection, especially in the P. vivax infection [50].

This study had limitations. First, there was a high level of bias in the study design of the enrolled studies that were reviewed. Second, there was a high level of heterogeneity among the studies examining co-infection as compared to malaria single infection (Moran’s I²: 94%). Third, we lacked the access to some full text papers because our university does not subscribe to some publishers which reported on the co-infection of both agents.

Since malaria and dengue frequently co-exist in the same geographical areas, there are some public health implications. In addition, the clinical outcomes of co-infection were more like dengue mono-infection than malaria mono-infection. Therefore, healthcare workers including physicians, medical technicians, and nurses need to collaborate with each other in order to solve the difficulty of differentiating between both diseases in similar areas. Using clinical outcomes such as fever with typical paroxysm, cerebral malaria, renal failure, and multi-organ failure might rule out patients with co-infection. On the other hand, using bleeding signs might indicate patients with co-infection. Moreover, screening for malaria parasite in patients with dengue infection might help to diagnose patients suspected with co-infection [24].

In conclusion, the study findings showed that dengue and malaria co-infection was associated with decreased odds of malaria infection, malaria parasitemia, AST, and ALT levels when compared to malaria mono-infection. However, malaria and dengue co-infection was associated with increased odds of platelet and hemoglobin levels when compared to malaria mono-infection.