Mosquitoes, flies, bugs and other vectors transmit viruses, parasites and bacteria that infect millions of people globally. They cause many diseases, including malaria, dengue, leishmaniases, Chagas disease and Zika virus disease.
The World Health Organization (WHO) has developed a new strategy to... strengthen vector control worldwide. Member States welcomed this integrated approach at the 2017 World Health Assembly and adopted a resolution to support the strategy.
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In the Region of the Americas, the leishmaniases are a group of diseases caused by various species of Leishmania, which cause a set of clinical syndromes in infected humans that can involve the skin, mucosa, and visceral organs. The spectrum of clinical disease is varied and depends on the interacti...on of several factors related to the parasite, the vector, and the host. Cutaneous leishmaniasis is the form most frequently reported in the Region and nearly 90% of cases present single or multiple localized lesions. Other cutaneous clinical forms, such as disseminated and diffuse cutaneous leishmaniasis, are more difficult to treat and relapses are common. The mucosal form is serious because it can cause disfigurement and severe disability if not diagnosed and treated early on. Visceral leishmaniasis is the most severe form, as it can cause death in up to 90% of untreated people.
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Parasites & Vectors volume 15, Article number: 389 (2022)
Dengue is one of the common arboviral infections and is a public health problem in South East Asia. The aim of this systematic review and meta-analysis was to evaluate the prevalence and distribution of dengue in SAARC (South Asian Associ...ation for Regional Cooperation) countries.
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Parasites & Vectors volume 11, Article number: 264 (2018)
Dengue creates a staggering epidemiological and economic burden for endemic countries. Without a specific therapy and with a commercial vaccine that presents some problems relative to its full effectiveness, initiatives to improve vector... control strategies, early disease diagnostics and the development of vaccines and antiviral drugs are priorities. In this study, we present the probable origins of dengue in America and the trajectories of its spread. Overall, dengue diagnostics are costly, making the monitoring of dengue epidemiology more difficult and affecting physicians’ therapeutic decisions regarding dengue patients, especially in developing countries. This review also highlights some recent and important findings regarding dengue in Brazil and the Americas. We also summarize the existing DENV polymerase chain reaction (PCR) diagnostic tests to provide an improved reference since these tests are useful and accurate at discriminating DENV from other flaviviruses that co-circulate in the Americas. Additionally, these DENV PCR assays ensure virus serotyping, enabling epidemiologic monitoring.
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Trypanosoma cruzi is the etiological agent of Chagas disease (CD), considered one of the most important parasitic infections in Latin America. Between 25 and 90 million humans are at infection risk via at least one of multiple infection mechanisms. Under natural conditions, the principal transmissio...n modes are transplacental or via one of more than 140 hematophagous triatomine bugs (Reduviidae: Triatominae). Triatomines acquire the parasite from mammal reservoirs due to their obligate blood-feeding (albeit triatomines can also feed on non-reservoir vertebrates such as birds and reptiles). The disease burden for CD in the Latin America and Caribbean region, based on disability-adjusted life-years (DALYs), is at least five times greater than that of malaria, and is approximately one-fifth that of HIV/AIDS. In recent decades, CD has extended to other continents outside natural reservoir or vector distributions due to human migration, with a minimum estimated 10 million individuals infected worldwide.
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Chagas disease caused by Trypanosoma cruzi is a public health issue in Latin America. This highly diverse parasite is divided into at least seven discrete typing units (DTUs) TcI-TcVI and Tcbat. Some DTUs have been associated with geographical distribution in epidemiological scenarios and clinical m...anifestations, but these aspects remain poorly understood. Many studies have focused on studying the parasite and its vectors/hosts, using a wide variety of genetic markers and methods. Here, we performed a systematic review of the literature for the last 20 years to present an update of DTUs distribution in the Americas, collecting ecoepidemiological information. We found that the DTUs are widespread across the continent and that there is a whole gamma of genetic markers used for the identification and genotyping of the parasite. The data obtained in this descriptor could improve the molecular epidemiology studies of Chagas disease in endemic regions.
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Epidemiology
Chagas disease (American trypanosomiasis) is caused by the protozoan parasite Trypanosoma cruzi, and transmitted to humans by infected triatomine bugs, and less commonly by transfusion, organ transplant, from mother to infant, and in rare instances, by ingestion of contaminated food or... drink.1-4 The hematophagous triatomine vectors defecate during or immediately after feeding on a person. The parasite is present in large numbers in the feces of infected bugs, and enters the human body through the bite wound, or through the intact conjunctiva or other mucous membrane.
Vector-borne transmission occurs only in the Americas, where an estimated 8 to 10 million people have Chagas disease.5 Historically, transmission occurred largely in rural areas in Latin America, where houses built of mud brick are vulnerable to colonization by the triatomine vectors.4 In such areas, Chagas disease usually is acquired in childhood. In the last several decades, successful vector control programs have substantially decreased transmission rates in much of Latin America, and large-scale migration has brought infected individuals to cities both within and outside of Latin America.
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Chagas disease (American trypanosomiasis) is caused by the protozoan parasite Trypanosoma cruzi, and transmitted to humans by infected triatomine bugs, and less commonly by transfusion, organ transplant, from mother to infant, and in rare instances, by ingestion of contaminated food or drink.1-4 The... hematophagous triatomine vectors defecate during or immediately after feeding on a person. The parasite is present in large numbers in the feces of infected bugs, and enters the human body through the bite wound, or through the intact conjunctiva or other mucous membrane.
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Human African trypanosomiasis (HAT) has been an alarming global public health issue. The disease affects mainly poor and marginalized people in low-resource settings and is caused by two subspecies of haemoflagellate parasite, Trypanosoma brucei and transmitted by tsetse flies. Progress made in HAT ...control during the past decade has prompted increasing global dialogue on its elimination and eradication. The disease is targeted by the World Health Organization (WHO) for elimination as a public health problem by 2020 and to terminate its transmission globally by 2030, along-side other Neglected Tropical Diseases (NTD). Several methods have been used to control tsetse flies and the disease transmitted by them. Old and new tools to control the disease are available with constraints.
Currently, there are no vaccines available. Efforts towards intervention to control the disease over the past decade have seen considerable progress and remarkable success with incidence dropping progressively, reversing the upward trend of reported cases. This gives credence in a real progress in its elimination. This study reviews various control measures, progress and a highlight of control issues, vector and parasite barriers that may have been hindering progress towards its elimination.
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This review focusses on the interactions between the etiologic agent of Chagas disease, Trypanosoma cruzi, and its triatomine vector. The flagellate mainly colonizes the intestinal tract of the insect. The effect of triatomines on trypanosomes is indicated by susceptibility and refractoriness phenom...ena that vary according to the combination of the strains. Other effects are apparent in the different regions of the gut. In the stomach, the majority of ingested blood trypomastigotes are killed while the remaining transform to round stages. In the small intestine, these develop into epimastigotes, the main replicative stage. In the rectum, the population density is the highest and is where the infectious stage develops, the metacyclic trypomastigote. In all regions of the gut, starvation and feeding of the triatomine affect T. cruzi. In the small intestine and rectum, starvation reduces the population density and more spheromastigotes develop. In the rectum, feeding after short-term starvation induces metacyclogenesis and after long-term starvation the development of specific cells, containing several nuclei, kinetoplasts and flagella. When considering the effects of T. cruzi on triatomines, the flagellate seems to be of low pathogenicity. However, during stressful periods, which are normal in natural populations, effects occur often on the behaviour, eg, in readiness to approach the host, the period of time before defecation, dispersal and aggregation. In nymphs, the duration of the different instars and the mortality rates increase, but this seems to be induced by repeated infections or blood quality by the feeding on infected hosts. Starvation resistance is often reduced by infection. Longevity and reproduction of adults is reduced, but only after infection with some strains of T. cruzi. Only components of the surface coat of blood trypomastigotes induce an immune reaction. However, this seems to act against gut bacteria and favours the development of T. cruzi.
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Leishmaniasis is a complex vector-borne disease involving in its transmission several species of protozoan parasites called Leishmania, a wide variety of animal reservoirs and phlebotomine sandflies vectors. Cutaneous Leishmaniasis (CL) is the most common form of the disease, and its clinical manife...stations vary from few papules to multiple ulcers affecting the skin but also the mucous membranes, leaving permanent scars and serious disability. It is a disfiguring and stigmatizing disease that often has a devastating psychosocial and economic impact on the affected resources limited communities.
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Leishmaniasis is a major vector-borne disease caused by obligate intramacrophage protozoa of the genus Leishmania, and transmitted by the bite of phlebotomine female sand flies of the genera Phlebotomus and Lutzomyia, in the old and new worlds, respectively. Among 20 well-recognized Leishmania speci...es known to infect humans, 18 have zoonotic nature, which include agents of visceral, cutaneous, and mucocutaneous forms of the disease, in both the old and new worlds. Currently, leishmaniasis show a wider geographic distribution and increased global incidence. Environmental, demographic and human behaviors contribute to the changing landscape for zoonotic cutaneous and visceral leishmaniasis. The primary reservoir hosts of Leishmania are sylvatic mammals such as forest rodents, hyraxes and wild canids, and dogs are the most important species among domesticated animals in the epidemiology of this disease. These parasites have two basic life cycle stages: one extracellular stage within the invertebrate host (phlebotomine sand fly), and one intracellular stage within a vertebrate host. Co-infection with HIV intensifies the burden of visceral and cutaneous leishmaniasis by causing severe forms and more difficult to manage. The disease is endemic to Ethiopia, and the clinical signs are not pathognomic. The visceral form (Kala-azar) may be confused with other similar conditions such as malaria, tropical splenomegaly, schistosomiasis, milliary tuberculosis, and brucellosis. Similarly, cutaneous leishmaniasis should be differentiated from disease like tropical ulcers, impetigo and leprosy. There are several methods of laboratory diagnosis of leishmaniasis, including parasitological, immunological and molecular. Different forms of treatments are available including oral, parenteral, and topical medications such as pentavalent antimonials, liposomal amphotericin B, miltefosine and paromomycin. Methods of control are largely limited to destruction of animal reservoirs, treatment of infected humans, and management of sand fly populations. Development of an effective vaccine against leishmaniasis has been largely unsuccessful and hinders its prevention.
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The major neglected tropical diseases, Taenia solium taeniosis/cysticercosis and schistosomiasis caused by Schistosoma mansoni or S. haematobium are presumed to be widely distributed in Africa. Taenia solium taeniosis/ cysticercosis has been reported as an emerging disease in different regions of Af...rica [1, 2], but currently the exact distribution remains unclear. Reported prevalences of T. solium taeniosis and cysticercosis in African countries are not extensive and are further complicated by the lack of ‘gold standard’ tests for diagnosis.
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Taenia saginata is a zoonotic tapeworm that is of economic importance in countries where cattle are kept. The parasite is transmitted from human tapeworm carriers (taeniosis) to bovines (cysticercosis) by excretion of eggs or proglottids containing eggs into the environment via the stool. Bovines ca...n then ingest the eggs through contaminated feed or water. After ingestion, the eggs hatch and release oncospheres in the small intestines, where the oncospheres penetrate the intestinal wall to reach the blood circulation. This distributes them throughout the body, but primarily to muscle tissue, where they develop into cysticerci. For humans to become infected with T. saginata, raw or undercooked bovine meat or offal containing infective cysts must be consumed. Bovine cysticercosis has been associated with various environmental factors related to water sources, such as animals having access to surface water, flooding of pastures and proximity to wastewater sources.
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Cutaneous leishmaniasis (CL) is a parasitic disease caused by infection with a vector-borne protozoan parasite of the genus Leishmania spp. The parasite is transmitted by the bite of an infected phlebotomine sand fly. Infection results in skin lesions which take a long time to heal and may leave per...manent, disfiguring scars (de Vries et al. 2015). CL is classified as a neglected tropical disease (NTD), and in common with several other NTDs, is associated with psychosocial effects including stigma, social exclusion, and declining mental health (Bailey et al. 2019; Bennis et al. 2018; Wenning et al. 2022). Emerging evidence suggests that people with CL are at a higher risk of experiencing anxiety, depression, decreased body satisfaction, loss of social status, and lower quality of life (Bennis et al. 2018; Yanik et al. 2004). The global mean age-standardised disability-adjusted life years (DALYs) lost by CL was 0.58 per 100,000 people (Karimkhani et al. 2016). Notably, this statistic only considers the physical effects of the lesions and does not account for the potentially considerable psychological and social effects of CL (Bailey et al. 2017; Bailey et al. 2019; Wenning et al. 2022).
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Leishmaniasis is a vector-borne disease with a wide variety of parasite species, reservoirs, and vectors involved in transmission. It is caused by different species of the protozoa Leishmania and is transmitted to animals and humans through a bite of insects in the Psychodidae family. Its presence i...s directly linked to poverty, but social, environmental, and climatalogic factors directly influence the disease's epidemiology.
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Leishmaniasis is found in people in focal areas of approximately 90 countries in the tropics, subtropics, and southern Europe. The ecologic settings range from rain forests to deserts. Leishmaniasis usually is more common in rural than in urban areas, but it is found in the outskirts of some cities.... Climate and other environmental changes have the potential to expand the geographic range of the sand fly vectors and the areas in the world where leishmaniasis is found.
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Leishmaniasis is a vector-borne disease with a broad global distribution and an increasing number of recorded cases worldwide. However, it is still one of the world's most neglected diseases. Over the last decades, the disease has been found to expand geographically with a global increase of cases o...f visceral and cutaneous leishmaniasis increasing the public health problems associated with the disease epidemics. The reported range expansion of the diseases has been associated with range expansions of vector populations in response to climate change. Leishmaniasis is caused by protozoan parasites of the genus Leishmania. The transmission can either be zoonotic and/or anthroponotic through the bite of an infected female phlebotomine sandfly. In Eurasia and Africa, all vector-competent sandfly species belong to the genus Phlebotomus. Cutaneous leishmaniasis (CL) is the most common form of leishmaniasis. In the ‘old world’, it is caused by five currently recognized Leishmania species: L. major, L. tropica and L. aethiopica (being main causative parasites) as well as L. infantum and L. donovani. Visceral leishmaniasis (VL), another common and more severe form of leishmaniasis, is only associated with the Leishmania species L. infantum and L. donovani. The specific Leishmania species cause different clinical symptoms in humans.
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The previous report of the WHO Expert Committee on this disease
followed a meeting in 1995. Intensive, coordinated efforts against HAT during
the intervening 18 years have resulted in a decrease in incidence to a point at
which elimination is considered feasible. This report provides informati...on about
new diagnostic approaches, new therapeutic regimens and better understanding
of the distribution of the disease with high-quality mapping. The roles of human
and animal reservoirs and the tsetse fly vectors that transmit the parasites are
emphasized. The new information has formed the basis for an integrated strategy
with which it is hoped that elimination of HAT will be achieved. The report also
contains recommendations on the approaches that will lead to elimination of the
disease.
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Background: The human helminth infections include ascariasis, trichuriasis, hookworm infections, schistosomiasis, lymphatic filariasis (LF) and onchocerciasis. It is estimated that almost 2 billion people worldwide are infected with helminths. Whilst the WHO treatment guidelines for helminth infecti...ons are mostly aimed at controlling morbidity, there has been a recent shift with some countries moving towards goals of disease elimination through mass drug administration, especially for LF and onchocerciasis. However, as prevalence is driven lower, treating entire populations may no longer be the most efficient or cost-effective strategy. Instead, it may be beneficial to identify individuals or demographic groups who are persistently infected, often termed as being “predisposed” to infection, and target treatment at them.
Methods: The authors searched Embase, MEDLINE, Global Health, and Web of Science for all English language, humanbased papers investigating predisposition to helminth infections published up to October 31st, 2017. The varying definitions used to describe predisposition, and the statistical tests used to determine its presence, are summarised. Evidence for predisposition is presented, stratified by helminth species, and risk factors for predisposition to infection are identified and discussed.
Results: In total, 43 papers were identified, summarising results from 34 different studies in 23 countries. Consistent evidence of predisposition to infection with certain species of human helminth was identified. Children were regularly found to experience greater predisposition to Ascaris lumbricoides, Schistosoma mansoni and S. haematobium than adults. Females were found to be more predisposed to A. lumbricoides infection than were males. Household clustering of infection was identified for A. lumbricoides, T. trichiura and S. japonicum. Ascaris lumbricoides and T. trichiura also showed evidence of familial predisposition. Whilst strong evidence for predisposition to hookworm infection was identified, findings with regards to which groups were affected were considerably more varied than for other helminth species.
Conclusion: This review has found consistent evidence of predisposition to heavy (and light) infection for certain human helminth species. However, further research is needed to identify reasons for the reported differences between demographic groups. Molecular epidemiological methods associated with whole genome sequencing to determine ‘who infects whom’ may shed more light on the factors generating predisposition.
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