Alteration in density of eosinophils in the cerebrospinal fluid of mice infected with Angiostrongylus cantonensis

The density of eosinophils in the cerebrospinal fluid (CSF) and blood of male ddY mice infected with Angiostrongylus cantonensis was examined on days 14, 20 and 27 post-infection (p.i.) with discontinuous Percoll gradient centrifugation. Normal blood eosinophils had a density of between 1.070 and 1.080 g ml-1. No significant changes in density in blood eosinophils were noted during the course of the observations. CSF eosinophils began to become hypodense (defined as density less than 1.070 g ml-1) on day 20 p.i., and 88% of eosinophils were hypodense on day 27. Our results suggest therefore that eosinophils probably become hypodense in the CSF and brain tissues, but not in the blood.     

Angiostrongylus cantonensis: role of eosinophils in the neurotoxic syndrome (Gordon-like phenomenon)

The role of eosinophils in the pathophysiology of Angiostrongylus cantonensis infections was investigated in nonpermissive (guinea pig) and permissive (rat) hosts. Neurological symptoms similar to the Gordon phenomenon (ataxia, tremor, paralysis) together with a loss of Purkinje cells in the cerebellum were observed after intracraneal injection of human eosinophil extracts or after infection with A. cantonensis, only in guinea pigs and not in rats. Blood eosinophilia as well as eosinophil numbers present in the cerebellum and in the cerebrospinal fluid were higher in guinea pigs than in rats, at all times after infection with A. cantonensis. Increased levels of cytotoxicity toward L3 larvae in vitro were obtained in the presence of guinea pig eosinophils and IgE antibodies, rather than with the corresponding rat effector system. The detection of one eosinophil granule component, the eosinophil peroxidase, in the cerebrospinal fluid from infected guinea pigs but not from rats suggested that in nonpermissive hosts, neurological disorders, similar to the previously described Gordon phenomenon, might be due to eosinophil neurotoxins released after interaction of eosinophils with the parasites.     

Cerebrospinal fluid eotaxin and eotaxin-2 levels in human eosinophilic meningitis associated with angiostrongyliasis

Eosinophilic meningitis associated angiostrongyliasis (EOMA) is a harmful disease of the brain and spinal cord caused by a parasitic helminth, Angiostrongylus cantonensis, presenting with severe headaches and cerebrospinal fluid (CSF) eosinophilia. However, the immunologic pathophysiology especially in relation to the eosinophilic inflammation is still unknown. We measured the CSF concentrations of eotaxin and eotaxin-2 of 30 patients and 10 controls. The CSF eotaxin and eotaxin-2 levels of the EOMA patients were significantly higher than those of the controls (p<0.001). The positive detection values were 83.3% (25/30) and 93.3% (28/30) for eotaxin and eotaxin-2, respectively. CSF eotaxin-2 levels also correlated with CSF eosinophilia (p=0.002). These results might indicate that the recruitment of eosinophils to the brain and spinal cord in EOMA patients could be related to elevated eotaxin-2 levels.     

Elevation of plasminogen activators in cerebrospinal fluid of mice with eosinophilic meningitis caused by Angiostrongylus cantonensis

A hallmark of parasitic meningitis is the infiltration of eosinophils into the subarachnoid space. Infection with Angiostrongylus cantonensis in mice induced proteinase activity in parallel with the pathological changes of eosinophilic meningitis. Zymogram analysis demonstrated that 70 and 55 kDa proteinases from cerebrospinal fluid (CSF) were active against the casein/plasminogen substrate. The proteinase activities were clearly inhibited by phenylmethanesulphonyl fluoride but not by ethylenediamine tetraacetic acid, 1,10-phenanthroline or leupeptin. Western blotting confirmed these enzymes to be tissue-type plasminogen activator and urokinase-type plasminogen activator, respectively. High activities of tissue-type plasminogen activator and urokinase-type plasminogen activator were detected in the CSF of mice with eosinophilic meningitis, and correlated positively with CSF eosinophil numbers and total protein, respectively. Immunohistochemistry demonstrated that tissue-type plasminogen activator and urokinase-type plasminogen activator localised in the endothelial cells of blood vessels, in blood clots and in infiltrated leukocytes. These results suggest that tissue-type plasminogen activator and urokinase-type plasminogen activator may be play a role in the pathogenesis of eosinophilic meningitis of angiostrongyliasis.     

Molecular diagnosis of eosinophilic meningitis due to Angiostrongylus cantonensis (Nematoda: Metastrongyloidea) by polymerase chain reaction-DNA sequencing of cerebrospinal fluids of patients

Cerebrospinal fluid (CSF) samples from clinically diagnosed patients with detectable Angiostrongylus canto-nensis-specific antibodies (n = 10), patients with clinically suspected cases that tested negative for A. cantonensis-an-tibodies (n = 5) and patients with cerebral gnathostomiasis (n = 2) and neurocysticercosis (n = 2) were examined by a single-step polymerase chain reaction (PCR) method using the AC primers for the 66-kDa native protein gene. The PCR method detected A. cantonensis DNA in CSF samples from four of 10 serologically confirmed angiostrongyliasis cases. The PCR results were negative for the remaining CSF samples. The nucleotide sequences of three positive CSF-PCR samples shared 98.8-99.2% similarity with the reference sequence of A. cantonensis. These results indicate the potential application of this PCR assay with clinical CSF samples for additional support in the confirmation of eosinophilic meningitis due to A. cantonensis.     

Detection of antibodies to Angiostrongylus cantonensis in serum and cerebrospinal fluid of patients with eosinophilic meningitis

Adult and young adult antigens of Angiostrongylus cantonensis were purified by immuno-affinity chromatography and used to detect antibody in serum and cerebrospinal fluid (CSF), by enzyme-linked immunosorbent assay (ELISA), in cases of human eosinophilic meningitis or meningoencephalitis. The levels of IgG, IgA, IgM and IgE antibodies to A. cantonensis in these patients were higher than levels in control subjects. Antibodies in patients detected against adult and young adult worm antigens of A. cantonensis did not differ significantly. Significantly higher IgM and IgE antibody levels were observed in serum compared with CSF from infected patients (Student's t-test, P less than 0.05). Both adult and young adult A. cantonensis antigens proved to be highly sensitive in ELISA for serum antibodies; however, the sensitivity was significantly lower in tests on CSF.     

Eosinophils in the cerebrospinal fluid of mice infected with Angiostrongylus cantonensis are resistant to apoptosis

Interleukin-5 (IL-5) transgenic mice were used to assess the immunological features of CSF eosinophils from mice infected with Angiostrongylus cantonensis. CSF eosinophils were hypodense by day 14 post infection (p.i.). CSF eosinophils survived longer in vitro than peritoneal eosinophils collected from cadmium sulphate (CdSO₄) -treated normal IL-5 transgenic mice. Apoptosis was measured by Annexin V binding and the presence of a distinct laddering pattern of DNA fragmentation on agarose electrophoresis. Regardless of the presence or absence of Actinomycin D, CSF eosinophils collected from IL-5 transgenic mice from days 15–36 p.i. exhibited less apoptosis than peritoneal eosinophils collected from uninfected IL-5 transgenic mice. CSF eosinophils collected from A. cantonensis infected C57BL/6 mice at days 15–34 p.i. showed elongation of survival time and less apoptosis during in vitro cultivation. Reduced apoptosis was noted only in CSF eosinophils, but not in peritoneal eosinophils recovered from the same infected IL-5 transgenic mice. CPP32/Caspase 3 activity of cultured peritoneal eosinophils from both infected and uninfected IL-5 transgenic mice was higher than that of cultured CSF eosinophils. Stimulation with A23187 readily induced apoptosis of peritoneal eosinophils, but not CSF eosinophils or peritoneal eosinophils cultured with mouse recombinant IL-5. The latter cells were morphologically identical to hypodense eosinophils. RT-PCR analysis indicated that bcl-2 and bcl-x_L mRNA expression was higher in CSF eosinophils compared with peritoneal eosinophils and this expression in the latter cells was upregulated after culture with mouse recombinant IL-5. These results suggest that CSF eosinophils, shifting to hypodense status through an accumulation from peripheral blood, are resistant to apoptosis. These changes may explain the long-lasting, helminthotoxic and neurotoxic actions of CSF eosinophils in A. cantonensis infection.     

Eosinophils in the cerebrospinal fluid of mice infected with Angiostrongylus cantonensis are resistant to apoptosis.

Interleukin-5 (IL-5) transgenic mice were used to assess the immunological features of CSF eosinophils from mice infected with Angiostrongylus cantonensis. CSF eosinophils were hypodense by day 14 post infection (p.i.). CSF eosinophils survived longer in vitro than peritoneal eosinophils collected from cadmium sulphate (CdSO₄) -treated normal IL-5 transgenic mice. Apoptosis was measured by Annexin V binding and the presence of a distinct laddering pattern of DNA fragmentation on agarose electrophoresis. Regardless of the presence or absence of Actinomycin D, CSF eosinophils collected from IL-5 transgenic mice from days 15–36 p.i. exhibited less apoptosis than peritoneal eosinophils collected from uninfected IL-5 transgenic mice. CSF eosinophils collected from A. cantonensis infected C57BL/6 mice at days 15–34 p.i. showed elongation of survival time and less apoptosis during in vitro cultivation. Reduced apoptosis was noted only in CSF eosinophils, but not in peritoneal eosinophils recovered from the same infected IL-5 transgenic mice. CPP32/Caspase 3 activity of cultured peritoneal eosinophils from both infected and uninfected IL-5 transgenic mice was higher than that of cultured CSF eosinophils. Stimulation with A23187 readily induced apoptosis of peritoneal eosinophils, but not CSF eosinophils or peritoneal eosinophils cultured with mouse recombinant IL-5. The latter cells were morphologically identical to hypodense eosinophils. RT-PCR analysis indicated that bcl-2 and bcl-x_L mRNA expression was higher in CSF eosinophils compared with peritoneal eosinophils and this expression in the latter cells was upregulated after culture with mouse recombinant IL-5. These results suggest that CSF eosinophils, shifting to hypodense status through an accumulation from peripheral blood, are resistant to apoptosis. These changes may explain the long-lasting, helminthotoxic and neurotoxic actions of CSF eosinophils in A. cantonensis infection.     

Molecular evidence for the endosymbiont <Emphasis Type="BoldItalic">Wolbachia</Emphasis> in a non-filaroid nematode, <Emphasis Type="BoldItalic">Angiostrongylus cantonensis</Emphasis>

Wolbachia harbored by most filarial parasites, is critical to both embryogenesis and microfilarial development, and may lead to inflammation and pathogenesis in infected hosts. Based on alignment of the sequences from the wsp, ftsZ, and 16S rRNA genes, Wolbachia was demonstrated to exist in Angiostrongylus cantonensis, a non-filaroid nematode. Although the wsp gene may not be the best candidate for evolutionary analysis of Wolbachia, this gene has been sequenced from a broader coverage of the host species, making it feasible to be used for phylogenetic analysis in this study. The results from both Neighbor-joining and Maximum parsimony methods showed that this novel Wolbachia does not belong to any of the known groups (C or D) of nematode-derived Wolbachia. In addition, the wsp gene sequence of this newly identified endosymbiont revealed a high degree of identity (98%) with that from Diaea circumlita c2, tentatively classified into the putative group G. This suggests that Wolbachia from A. cantonensis could represent a deeply branched lineage in Wolbachia evolution or the occurrence of horizontal transfer between infected hosts. In conclusion, the findings provide some insights into our understanding of the evolution of Wolbachia, particularly the isolate from A. cantonensis.     

Development of brain injury in mice by Angiostrongylus cantonensis infection is associated with the induction of transcription factor NF-kappaB, nuclear protooncogenes, and protein tyrosine phosphorylation

Eosinophilic meningitis or meningoencephalitis caused by Angiostrongylus cantonensis is endemic to the Pacific area of Asia, especially Taiwan, Thailand, and Japan. Although eosinophilia is an important clinical manifestation of A. cantonensis infection, the role of eosinophils in the progress of the infection remains to be elucidated. In this experiment, we showed that A. cantonensis-caused eosinoplia and inflammation might lead to the induction of NF-kappaB and protooncogene expression via activation of the tyrosine phosphorylation signal pathway. After mice were infected daily with 30 third-stage larvae of A. cantonensis by oral adminstration for 6 weeks, no significant differences PKC-alpha, MEK-1, ERK-2, JNK, and p38 protein expression were found between the control and infected mice. However, the protein tyrosine phosphorylation levels, NF-kappaB, and iNOS protein products were significantly increased by 3.5-, 3.3-, and 6.3-fold, respectively, after 3 weeks of A. cantonensis infection. The same pattern was found for c-Myc, c-Jun, and c-Fos proteins, which were elevated by 3.2-, 2.3-, and 3.4-fold, respectively, compared to control animals after 3 weeks. The expression potency of these proteins started increasing in week 1, reaching maximal induction in week 3, and then declining in week 5 after A. cantonensis infection. Another consistent result was noted in the pathological observations, including eosinophilia, leukocyte infiltration, granulomatous reactions, and time responses in brain tissues of infected mice. These data suggest that the development of brain injury by eosinophlia of A. cantonensis infection is associated with NF-kappaB and/or nuclear protooncogenes expression, which is activated by the tyrosine phosphorylation pathway.     

Induced eosinophilia and proliferation in Angiostrongylus cantonensis-infected mouse brain are associated with the induction of JAK/STAT1, IAP/NF-kappaB and MEKK1/JNK signals

Eosinophilic meningitis or meningoencephalitis caused by Angiostrongylus cantonensis is endemic to the Pacific area of Asia, especially Taiwan, Thailand, and Japan. Although eosinophilia is an important clinical manifestation of A. cantonensis infection, the role of eosinophils in the progress of the infection remains to be elucidated. In this experiment, we show that A. cantonensis-induced eosinophilia and inflammation might lead to the induction of IAP/NF-kappaB, JAK/STAT1 and MEKK1/JNK signals. The phosphorylation levels of JAK and JNK, STAT1, IAP, NF-kappaB and MEKK1 protein products were significantly increased after 12 days or 15 days of A. cantonensis infection. However, no significant differences in MAPKs such as Raf, MEK-1, ERK1/2 and p38 expression were found between control and infected mice. The activation potency of JAK/STAT1, IAP/NF-kappaB and MEKK1/JNK started increasing on day 3, with significant induction on day 12 or day 15 after A. cantonensis infection. Consistent results were noted in the pathological observations, including eosinophilia, leukocyte infiltration, granulomatous reactions, and time responses in the brain tissues of infected mice. These data suggest that the development of brain injury by eosinophilia of A. cantonensis infection is associated with activation of JAK/STAT1 signals by cytokines, and/or activation of MEKK1/JNK by oxidant stress, and/or activation of NF-kappaB by increasing IAP expression.     

Neuro-angiostrongyliasis: unresolved issues

Angiostrongylus cantonensis, the rat lungworm, probably evolved with its hosts, members of the genus Rattus and closely related species, in south-east Asia. Since its first discovery in rats in China and in a case of human infection in Taiwan, the parasite has been found to infect humans and other mammals across a wide and ever-increasing territory, which now encompasses much of south-east Asia, Melanesia, Polynesia and eastern Australia. It has also established a foothold in Africa, India, the Caribbean and south-eastern USA. This dispersal has been a direct result of human activity, and in some cases has been linked with the spread of the African giant land snail, Achatina fulica. However, this snail is not critical to the extension of the parasite's range, as numerous other indigenous molluscan species serve as adequate intermediate hosts; the importance of Achatina to the life cycle may have been over-emphasized. In Australia, the parasite is established along parts of the east coast, and the presence of an indigenous close relative, Angiostrongylus mackerrasae, suggests a long association of the parasite with its local rat hosts, a situation analogous to that of Angiostrongylus malaysiensis in south-east Asia. These three Angiostrongylus species share virtually the same life cycle, but only A. cantonensis has been confirmed to be a human pathogen.     

Parastrongylus (=Angiostrongylus) cantonensis now endemic in Louisiana wildlife

Parastrongylus (=Angiostrongylus) cantonensis, a lung worm of rats, was first reported in the United States in 1987, with a probable introduction by infected rats from ships docking in New Orleans, Louisiana, during the mid-1980s. Since then, it has been reported in nonhuman primates and a boy from New Orleans, and in a horse from Picayune, Mississippi, a distance of 87 km from New Orleans. Parastrongylus cantonensis infection is herein reported in a lemur (Varencia variegata rubra) from New Iberia, Louisiana, a distance of 222 km from New Orleans, and in a wood rat (Neotomafloridanus) and in 4 opossums (Didelphis virginiana) from Baton Rouge, Louisiana, a distance of 124 km from New Orleans. The potential of a great variety of gastropods serving as intermediate hosts in Louisiana may pose a threat to wildlife as well as to domesticated animals in the areas where infected Norway rats (Rattus norvegicus) are present.     

The suitability of several aquatic snails as intermediate hosts for Angiostrongylus cantonensis.

Sixteen species of aquatic snails of four families were tested by quantitative technique under standardized conditions for their suitability as intermediate hosts for Angiostrongylus cantonensis. These species were the planorbid snails Biomphalaria glabrata, Biomphalaria alexandrina, Planorbis planorbis, Planorbis intermixtus, Bulinus truncatus, Bulinus contortus, Bulinus africanus, Bulinus tropicus and Helisoma sp.; the lymnaeid snails Lymnaea natalensis, Lymnaea tomentosa, Lymnaea stagnalis, and Stagnicola elodes; the physid snail Physa acuta (an Egyptian and a German strain) and the ampullariid snails Marisa cornuarietis and Lanistes carinatus. All these snail species proved to be susceptible to infection with A. cantonensis, and first stage larvae reached the infective third stage in all of them. However, the rate and intensity of infection varied with different species. B. glabrata was the most susceptible snail species with a 100% infection rate and an average percentage recovery of third stage larvae of 26.1. This was followed by S. elodes and B. africanus, with a 100% infection rate and an average percentage recovery of third stage larvae of 15.6 and 14.6 respectively. The rest of snail species proved to be less susceptible. For comparative evaluation of the suitability of the various snail species as intermediate hosts of A. cantonensis a "Capacity Index" was determined. This index should provide a useful method for the evaluation of the suitability of various snails as intermediate hosts of nematode parasites under standardized conditions in the laboratory.     

Prevalence and intensity of Angiostrongylus cantonensis in freshwater snails in relation to some ecological and biological factors

The purpose of the study was to record different intermediate hosts of A. cantonensis and to determine the infection prevalence and intensity of this parasite in freshwater snails in relation to some ecological and biological factors. The study was conducted at Al-Salam irrigation Canal and Al-Abtal village (north Sinai) for one year, from March 2004 to February 2005. Thirteen species of freshwater snails of nine families were examined for A. cantonensis infection. Six species were found infected with A. cantonensis larvae. These species were L. carinatus, C. bulimoides, C. cyclostomoides, B. alexandrina, L. natalensis and M. tuberculta. The infection prevalence of A. cantonensis in the examined snails ranged from 0.63 to 2.24%. L. carinatus snail had the highest prevalence, mean abundance and mean intensity of A. cantonensis infection. Positive correlations were found between both prevalence and mean abundance of A. cantonensis and host size in L. carinatus and M. tuberculata. Negative correlations were detected between salinity and prevalence, mean abundance and mean intensity of larvae of A. cantonensis. The results demonstrated seasonal and spatial variation in the prevalence, mean abundance and mean intensity of infection among examined snails. In this study, A. cantonensis larvae were found in a wide range of freshwater snails and M. tuberculata snail was recorded as a new intermediate host for the first time. In conclusion, further investigations in other areas and controlled laboratory experiments of infection approaches are required to evaluate the possible threat of this parasite on humans.     

Postnatal mammary gland development requires macrophages and eosinophils

Interactions between mammary epithelial and mesenchymal cells including fibroblasts and adipocytes are crucial for the proper postnatal development of the mammary ductal tree. Often overlooked, however, are the migrant cells that enter tissues at different stages of development. In this paper we identify two such cell types, macrophages and eosinophils, that are recruited around the growing terminal end buds (TEBs) during postnatal development. An important role for leukocytes in mammary gland ductal outgrowth is first demonstrated by depleting mice of leukocytes using sub-lethal (gamma)-irradiation. This treatment results in a curtailment of mammary gland epithelial development that is completely rescued by bone-marrow transplantation, concurrent with a restoration of macrophage and eosinophil recruitment around the growing ducts. Using mice homozygous for a null mutation in the gene for CSF1 (Csfm(op)/Csfm(op)), the major growth factor for macrophages, we show that in the absence of CSF1, the population of macrophages in mammary glands is depleted. In this mutant, the formation of TEBs, their outgrowth into the fat pad and the branching of the resultant ducts are all impaired. Similarly, by using mice homozygous for a null mutation in the gene for eotaxin, a major chemokine for local recruitment of eosinophils in tissue, we identify eotaxin as the necessary and sufficient chemokine responsible for eosinophil recruitment around TEBs. In the absence of eosinophils, mammary gland branch formation and to a lesser extent TEB formation are reduced. Our data show that CSF1-regulated macrophages, in collaboration with eotaxin-regulated eosinophils, have essential and complementary functions in regulating the branching morphogenesis of the mammary gland.     

Angiostrongylus cantonensis eosinophilic meningitis: A clinical study of 42 consecutive cases in French Polynesia

IntroductionIn endemic areas, eosinophilic meningitis is mainly caused by Angiostrongylus cantonensis. We describe a series of this poorly-known condition.MethodsRetrospective cohort study (2000–2012) including all patients diagnosed with eosinophilic meningitis in French Polynesia.ResultsForty-two patients (males: 61.9%, age: 22 (IQR 17–32)) were diagnosed with a serologically proven (n = 13) or probable A. cantonensis meningitis, mostly during the dry season (66.6%) and following the consumption of or prolonged contact with an intermediate/paratenic host (64.3%). No differential diagnosis was found in probable cases, in whom serological tests were performed earlier (7.5 days (6.5–10)) compared to positive patients (7.5 (6.5–10) versus 11 (7–30) days, p = 0.02). The most commonly reported symptom was headache (92.8%). Fever (7.1%) and biological inflammatory syndrome (14.3%) were rare. Blood eosinophil count was 1200/mm³ (900–2548). Cerebrospinal fluid (CSF) analysis disclosed a protein level of 0.9 g/L (0.7–1.1), a CSF/plasma glucose ratio of 0.50 (0.40–0.55), and 500 leucocytes/mm³ (292–725; eosinophils: 42.0% (29.5–60); lymphocytes: 46.5% (32.5–59.0)). Thirteen cases (31.0%) were severe, with 11 focal neurological deficits. A delayed hospital referral (OR 1.13, p = 0.05) was associated with severity.ConclusionsA. cantonensis meningitis must be evocated in young patients with meningitic syndrome, severe headache, and CSF inflammation with predominance of eosinophils.     

Correlated evolution between host immunity and parasite life histories in primates and oxyurid parasites

Maturation time is a pivotal life-history trait of parasitic nematodes, determining adult body size, as well as daily and total fecundity. Recent theoretical work has emphasized the influence of prematurational mortality on the optimal values of age and size at maturity in nematodes. Eosinophils are a family of white blood cells often associated with infections by parasitic nematodes. Although the role of eosinophils in nematode resistance is controversial, recent work has suggested that the action of these immune effectors might be limited to the larval stages of the parasite. If eosinophils act on larval survival, one might predict, in line with theoretical models, that nematode species living in hosts with large eosinophil numbers should show reduced age and size at maturity. We tested this prediction using the association between the pinworms (Oxyuridae, Nematoda) and their primate hosts. Pinworms are highly host specific and are expected to be involved in a coevolutionary process with their hosts. We found that the body size of female parasites was negatively correlated with eosinophil concentration, whereas the concentration of two other leucocyte families-neutrophils and lymphocytes-was unrelated to female body size. Egg size of parasites also decreased with host eosinophil concentration, independently of female size. Male body size was unrelated to host immune parameters. Primates with the highest immune defence, therefore, harbour small female pinworms laying small eggs. These results are in agreement with theoretical expectations and suggest that life histories of oxyurid parasites covary with the immune defence of their hosts. Our findings illustrate the potential for host immune defence as a factor driving parasite life-history evolution.     

Meningitis patients with Angiostrongylus cantonensis may present without eosinophilia in the cerebrospinal fluid in northern Vietnam

BackgroundEosinophilic meningitis (EM) is a rare clinical syndrome caused by both infectious and noninfectious diseases. In tropical pacific countries, Angiostrongylus cantonensis is the most common cause. However, the EM definition varies in the literature, and its relation to parasitic meningitis (PM) remains unclear.Methodology/Principal findingsAdult and adolescent patients of 13 years old or above with suspected central nervous system (CNS) infections with abnormal CSF findings were prospectively enrolled at a tertiary referral hospital in Hanoi, Vietnam from June 2012 to May 2014. Patients with EM or suspected PM (EM/PM) were defined by the presence of either ≥10% eosinophils or an absolute eosinophil cell counts of ≥10/mm³ in the CSF or blood eosinophilia (>16% of WBCs) without CSF eosinophils. In total 679 patients were enrolled: 7 (1.03%) had ≥10% CSF eosinophilia, 20 (2.95%) had ≥10/mm³ CSF eosinophilia, and 7 (1.03%) had >16% blood eosinophilia. The patients with ≥10% CSF eosinophilia were significantly younger (p = 0.017), had a lower body temperature (p = 0.036) than patients with ≥10/mm³ CSF eosinophilia among whom bacterial pathogens were detected in 72.2% (13/18) of those who were tested by culture and/or PCR. In contrast, the characteristics of the patients with >16% blood eosinophilia resembled those of patients with ≥10% CSF eosinophilia. We further conducted serological tests and real-time PCR to identify A. cantonensis. Serology or real-time PCR was positive in 3 (42.8%) patients with ≥10% CSF eosinophilia and 6 (85.7%) patients with >16% blood eosinophilia without CSF eosinophils but none of patients with ≥10/mm³ CSF eosinophilia.ConclusionsThe etiology of PM in northern Vietnam is A. cantonensis. The eosinophil percentage is a more reliable predictor of parasitic EM than absolute eosinophil count in the CSF. Patients with PM may present with a high percentage of eosinophils in the peripheral blood but not in the CSF.     

Public health importance of Angiostrongylus cantonensis and its relatives

Species of Angiostrongylus are fairly common nematode parasites of a variety of small mammals, but some species - particularly A. cantonensis and A. costaricensis - are increasingly seen as human infections. The worms make use of a range of aquatic, amphibious or terrestrial gastropod molluscs as intermediate hosts, which become infected by ingestion of eggs shed in the faeces of infected mammals. Porotenic hosts, including crustaceans, amphibians and reptiles, are known for most Angiostrongylus species, and can also be a source of the infective third-stage larvae that initiate mammalian infections.