HTLV-I and Strongyloides in Australia: The worm lurking beneath

Peculiar transcriptional reprogramming with functional impairment of dendritic cells upon exposure to transformed HTLV-1-infected cells

Manipulation of immune cell functions, independently of direct infection of these cells, emerges as a key process in viral pathophysiology. Chronic infection by Human T-cell Leukemia Virus type 1 (HTLV-1) is associated with immune dysfunctions, including misdirected responses of dendritic cells (DCs). Here, we interrogate the ability of transformed HTLV-1-infected T cells to manipulate human DC functions. We show that exposure to transformed HTLV-1-infected T cells induces a biased and peculiar transcriptional signature in monocyte-derived DCs, associated with an inefficient maturation and a poor responsiveness to subsequent stimulation by a TLR4 agonist. This poor responsiveness is also associated with a unique transcriptional landscape characterized by a set of genes whose expression is either conferred, impaired or abolished by HTLV-1 pre-exposure. Induction of this functional impairment requires several hours of coculture with transformed HTLV-1-infected cells, and associated mechanisms driven by viral capture, cell-cell contacts, and soluble mediators. Altogether, this cross-talk between infected T cells and DCs illustrate how HTLV-1 might co-opt communications between cells to induce a unique local tolerogenic immune microenvironment suitable for its own persistence.

Strongyloidiasis

Strongyloidiasis is a neglected tropical disease caused primarily by the roundworm Strongyloides stercoralis. Strongyloidiasis is most prevalent in Southeast Asia and the Western Pacific. Although cases have been documented worldwide, global prevalence is largely unknown due to limited surveillance. Infection of the definitive human host occurs via direct skin penetration of the infective filariform larvae. Parasitic females reside in the small intestine and reproduce via parthenogenesis, where eggs hatch inside the host before rhabditiform larvae are excreted in faeces to begin the single generation free-living life cycle. Rhabditiform larvae can also develop directly into infectious filariform larvae in the gut and cause autoinfection. Although many are asymptomatic, infected individuals may report a range of non-specific gastrointestinal, respiratory or skin symptoms. Autoinfection may cause hyperinfection and disseminated strongyloidiasis in immunocompromised individuals, which is often fatal. Diagnosis requires direct examination of larvae in clinical specimens, positive serology or nucleic acid detection. However, there is a lack of standardization of techniques for all diagnostic types. Ivermectin is the treatment of choice. Control and elimination of strongyloidiasis will require a multifaceted, integrated approach, including highly sensitive and standardized diagnostics, active surveillance, health information, education and communication strategies, improved water, sanitation and hygiene, access to efficacious treatment, vaccine development and better integration and acknowledgement in current helminth control programmes.

Locally acquired strongyloidiasis in remote Australia: why are there still cases?

In Australia, strongyloidiasis primarily affects returned travellers, Vietnam veterans and refugees or asylum seekers, and First Nations people. Non-overseas acquired cases are seen almost exclusively in Australian First Nations remote communities. Australian First Nations communities have one of the highest rates of strongyloidiasis in the world. Our work has shown that strongyloidiasis is a disease of poverty. Acknowledging this is important-we need to shift the lens to socioeconomic factors, particularly environmental health hardware such as working toilets and sewerage systems, showers and laundries, and effective wastewater and rubbish removal. The rates of strongyloidiasis in First Nations communities is a result of decades of inadequate, poorly constructed and/or poorly maintained housing, and poor environmental health hardware (hereafter hardware). The solution lies in adequate funding, resulting in well designed and maintained housing and appropriate hardware. Governments need to allow First Nations communities themselves to take the lead role in funding allocation, and design, construction and maintenance of their housing and hardware. This will ensure housing and hardware fulfils cultural and physical needs and desires, and protects health. Improving housing and hardware will also improve other health outcomes. This article is part of the Theo Murphy meeting issue 'Strongyloides: omics to worm-free populations'.

New Perspectives about Drug Candidates Targeting HTLV-1 and Related Diseases

Among the human T-lymphotropic virus (HTLV) types, HTLV-1 is the most prevalent, and it has been linked to a spectrum of diseases, including HAM/TSP, ATLL, and hyperinfection syndrome or disseminated strongyloidiasis. There is currently no globally standard first-line treatment for HTLV-1 infection and its related diseases. To address this, a comprehensive review was conducted, analyzing 30 recent papers from databases PubMed, CAPES journals, and the Virtual Health Library (VHL). The studies encompassed a wide range of therapeutic approaches, including antiretrovirals, immunomodulators, antineoplastics, amino acids, antiparasitics, and even natural products and plant extracts. Notably, the category with the highest number of articles was related to drugs for the treatment of ATLL. Studies employing mogamulizumab as a new perspective for ATLL received greater attention in the last 5 years, demonstrating efficacy, safe use in the elderly, significant antitumor activity, and increased survival time for refractory patients. Concerning HAM/TSP, despite corticosteroid being recommended, a more randomized clinical trial is needed to support treatment other than corticoids. The study also included a comprehensive review of the drugs used to treat disseminated strongyloidiasis in co-infection with HTLV-1, including their administration form, in order to emphasize gaps and facilitate the development of other studies aiming at better-directed methodologies. Additionally, docking molecules and computer simulations show promise in identifying novel therapeutic targets and repurposing existing drugs. These advances are crucial in developing more effective and targeted treatments against HTLV-1 and its related diseases.

Neglected tropical diseases in Australia: a narrative review

•Neglected tropical diseases (NTDs) represent a threat to the health, wellbeing and economic prosperity of billions of people worldwide, often causing serious disease or death. •Commonly considered diseases of low and middle-income nations, the presence of NTDs in high income countries such as Australia is often overlooked. •Seven of the 20 recognised NTDs are endemic in Australia: scabies, soil-transmitted helminths and strongyloidiasis, echinococcosis, Buruli ulcer, leprosy, trachoma, and snakebite envenoming. •Dengue, while not currently endemic, poses a risk of establishment in Australia. There are occasional outbreaks of dengue fever, with local transmission, due to introductions in travellers from endemic regions. •Similarly, the risk of introduction of other NTDs from neighbouring countries is a concern. Many NTDs are only seen in Australia in individuals travelling from endemic areas, but they need to be recognised in health settings as the potential consequences of infection can be severe. •In this review, we consider the status of NTDs in Australia, explore the risk of introducing and contracting these infections, and emphasise the negative impact they have on the health of Australians, especially Aboriginal and Torres Strait Islander peoples.

Strongyloides stercoralis infection in dogs in Austria: two case reports

Background

Strongyloides stercoralis is endemic in tropical and subtropical regions, but reports of infections in central and northern Europe have been recently increasing. Infections occur mainly in humans and dogs. In dogs, both dog-adapted and zoonotic S. stercoralis genotypes seem to occur. Clinical manifestations mainly include gastrointestinal and respiratory signs. The severity of the disease can vary greatly and depends on the immune status of the host. The infection is potentially fatal in immunosuppressed individuals, either medically induced or due to an underlying disease, in which hyperinfections and disseminated infections with extraintestinal parasite dissemination may occur.

Methods

Diagnosis was based on coproscopy, including flotation and the Baermann funnel technique, histology of small intestinal biopsies and molecular analysis of mitochondrial cytochrome oxidase subunit I (COI) and hypervariable regions I and IV (HVR I and HVR IV) of the nuclear 18S rDNA loci.

Results

Two independent cases of severe canine S.stercoralis infection in Austria are presented. In both cases, S. stercoralis was detected in histological sections of the small intestine and with the Baermann funnel technique. Molecular analysis revealed strains with zoonotic potential. Case 1 was a 1-year-old female French bulldog with a long history of respiratory and gastrointestinal signs, severe emaciation and apathy before S.stercoralis infection was diagnosed. Treatment with moxidectin (2.5 mg/kg body weight [BW], oral route) did not eliminate the infection, but treatment with ivermectin (0.2 mg/kg BW, subcutaneously) was successful. Case 2 consisted of two 2-month-old Pomeranian puppies, one female and one male, from a litter of four, which died soon after presenting dyspnoea and haemorrhagic diarrhoea (female) or torticollis (male); S.stercoralis infection was first diagnosed post-mortem.

Conclusion

More attention should be paid to this nematode because although it appears to be rare in Austria, it is easily overlooked on standard coproscopy unless a Baermann funnel technique is used, and even then, it can be missed. Moxidectin is not always successful in eliminating the infection, and treatment with ivermectin should be considered in cases of infection.

Graphical Abstract

Hospitalizations Associated with Strongyloidiasis in the United States, 2003-2018

BACKGROUND

Strongyloides stercoralis is considered to be historically endemic in Appalachia and the American South, but recent surveillance data, especially data evaluating strongyloidiasis associated with hospitalization, are lacking in most parts of the US.

METHODS

We performed a population-based retrospective analysis on strongyloidiasis using the National Inpatient Sample from 2003-2018. Geographic distribution of strongyloidiasis associated hospitalization was assessed. Logistic regression was used to identify risk factors associated with strongyloidiasis.

RESULTS

We identified 6931 hospitalizations associated with strongyloidiasis during the study period (11.8 per million hospitalizations). The rate of strongyloidiasis was highest in the US Northeast region including the Middle Atlantic division (47.1 cases per million population, adjusted odds ratio, aOR: 2.00 [95% confidence interval, CI: 1.58-2.53]), and the East South Central division (27.5 cases per million population, adjusted odds ratio, aOR: 2.77 [95% confidence interval, CI: 2.02-3.80]). Older age, male sex, non-white race/ethnicity particularly Hispanic and Asian, non-private insurance, and residence in neighborhoods with low median income were also associated with strongyloidiasis. Immunocompromising conditions, particularly human immunodeficiency virus infection, were present in 41.3% of hospitalizations with strongyloidiasis. In-hospital death was seen in 7.8% of cases with strongyloidiasis-associated hospitalization.

CONCLUSIONS

Strongyloidiasis-associated hospitalization is rare in the U.S. but can be associated with mortality. It occurs more frequently in poor and marginalized populations. Immunocompromised conditions were common among hospitalized patients with strongyloidiasis. Enhanced surveillance efforts are needed to inform health policies for improving the health of at-risk populations.

The Association between Diabetes and Human T-Cell Leukaemia Virus Type-1 (HTLV-1) with Strongyloides stercoralis: Results of a Community-Based, Cross-Sectional Survey in Central Australia

In central Australia, an area that is endemic for the human T-cell leukaemia virus type-1 (HTLV-1), the prevalence of Strongyloides stercoralis and its association with other health conditions are unknown. A cross-sectional community-based survey was conducted in seven remote Aboriginal communities in central Australia, from 2014 to 2018. All residents aged ≥10 years were invited to complete a health survey and to provide blood for Strongyloides serology, HTLV-1 serology and HTLV-1 proviral load (PVL). Risk factors for Strongyloides seropositivity and associations with specific health conditions including diabetes and HTLV-1 were determined using logistic regression. Overall Strongyloides seroprevalence was 27% (156/576) (children, 22% (9/40); adults (≥15 years), 27% (147/536), varied widely between communities (5–42%) and was not associated with an increased risk of gastrointestinal, respiratory or dermatological symptoms. Increasing age, lower HTLV-1 PVL (<1000 copies per 105 peripheral blood leucocytes) compared to the HTLV-1 uninfected group and community of residence were significant risk factors for Strongyloides seropositivity in an adjusted model. A modest reduction in the odds of diabetes among Strongyloides seropositive participants was found (aOR 0.58, 95% CI 0.35, 1.00; p = 0.049); however, this was lost when body mass index was included in the adjusted model (aOR 0.48, 95% CI 0.48, 1.47; p = 0.542). Strongyloides seropositivity had no relationship with anaemia. Exploring social and environmental practices in communities with low Strongyloides seroprevalence may provide useful lessons for similar settings.

Seropositivity and geographical distribution of Strongyloides stercoralis in Australia: A study of pathology laboratory data from 2012-2016

Background

There are no national prevalence studies of Strongyloides stercoralis infection in Australia, although it is known to be endemic in northern Australia and is reported in high risk groups such as immigrants and returned travellers. We aimed to determine the seropositivity (number positive per 100,000 of population and percent positive of those tested) and geographical distribution of S. stercoralis by using data from pathology laboratories.

Methodology

We contacted all seven Australian laboratories that undertake Strongyloides serological (ELISA antibody) testing to request de-identified data from 2012–2016 inclusive. Six responded. One provided positive data only. The number of people positive, number negative and number tested per 100,000 of population (Australian Bureau of Statistics data) were calculated including for each state/territory, each Australian Bureau of Statistics Statistical Area Level 3 (region), and each suburb/town/community/locality. The data was summarized and expressed as maps of Australia and Greater Capital Cities.

Principal findings

We obtained data for 81,777 people who underwent serological testing for Strongyloides infection, 631 of whom were from a laboratory that provided positive data only. Overall, 32 (95% CI: 31, 33) people per 100,000 of population were seropositive, ranging between 23/100,000 (95% CI: 19, 29) (Tasmania) and 489/100,000 population (95%CI: 462, 517) (Northern Territory). Positive cases were detected across all states and territories, with the highest (260-996/100,000 and 17–40% of those tested) in regions across northern Australia, north-east New South Wales and north-west South Australia. Some regions in Greater Capital Cities also had a high seropositivity (112-188/100,000 and 17–20% of those tested). Relatively more males than females tested positive. Relatively more adults than children tested positive. Children were under-represented in the data.

Conclusions/Significance

The study confirms that substantial numbers of S. stercoralis infections occur in Australia and provides data to inform public health planning.

Strongyloides stercoralis, a parasitic roundworm, is endemic in many countries world-wide. In Australia, groups at risk for strongyloidiasis include Aboriginal and/or Torres Strait Islander people, who acquired this parasite locally, and immigrants and returned travellers who acquired the infection outside Australia. We obtained deidentified results of ELISA IgG antibody tests for Strongyloides from diagnostic pathology laboratories during 2012 to 2016 and calculated the number of people who were positive at least once and the number who never had a positive result. We drew maps showing the number positive per 100,000 of population, the percent positive of those tested, and the number tested/100,000 for each region and the number positive in each suburb of residence according to the Australian Bureau of Statistics. The highest seropositivity (260-996/100,000 of population) was in Northern Australia, north-west South Australia and north-east New South Wales where many Aboriginal and Torres Strait Islander people live in remote communities. There were also some regions in Greater Capital Cities with a high number of people positive per 100,000 of population (112-188/100,000), likely reflecting higher populations of immigrants and returned travellers who were infected outside Australia.