Experimental transmission of nocturnally periodic Wuchereria bancrofti to Indian leaf monkey (Presbytis entellus)

A case study of risk factors for lymphatic filariasis in the Republic of Congo

BACKGROUND

Little is known regarding risk factors for lymphatic filariasis (LF) in Central Africa. We studied the epidemiology of LF in an endemic village in the Republic of Congo.

METHODS

Dependent variables were Wuchereria bancrofti antigenemia (ICT card test) and microfilaremia (night blood smears). The following factors were investigated: sex, age, bed net, latrines, source of water, uptake of anthelmintic drugs, hunting/fishing activities, and occasionally sleeping in the bush. Mixed multivariate logistic regression models were used.

RESULTS

134 of 774 subjects aged ≥ 5 years (17.3%) had W. bancrofti antigenemia and 41 (5.3%) had microfilaremia (mf). Infection rates increased with age up to roughly 20 years and remained stable thereafter. Multivariate analysis of antigenemia demonstrated an increased risk for males (OR = 2.0 [1.3-3.0]) and for people who hunt or fish (OR = 1.5 [1.0-2.4]) and a protective effect of latrines (OR = 0.5 [0.4-0.8]). Among males, those hunting or fishing at night had an increased risk for antigenemia (OR = 1.9 [1.1-3.5]), and use of latrines was protective (OR = 0.5 [0.3-0.9]). For females, bed nets were protective (OR = 0.4 [0.1-0.9]), and there was a strong household effect (intraclass correlation coefficient [ICC]: 0.24). When mf was used as the dependent variable, males had a higher risk for infection (OR = 5.4 [2.1-13.4]), latrines had a protective effect (OR = 0.4 [0.1-0.9]) and there was a marked household effect (ICC = 0.49).

CONCLUSIONS

Age, sex, and occupation-dependent exposure to mosquitoes were important risk factors for infection with W. bancrofti in this study. It is likely that men often acquire infection in high transmission areas outside of the village, while children and women are infected in areas with lower transmission inside or near the village. Additional studies are needed to determine whether these findings apply to other areas in Central Africa.

A review of the complexity of biology of lymphatic filarial parasites

There are about five more common, including Wuchereria bancrofti and Brugia malayi, and four less common filarial parasites infecting human. Genetic analysis of W. bancrofti populations in India showed that two strains of the species are prevalent in the country. The adult filarial parasites are tissue specific in the human host and their embryonic stage, called microfilariae (mf), are found in the blood or skin of the host, depending upon the species of the parasite. Three genetically determined physiological races exist in W. bancrofti and B. malayi, based on the microfilarial periodicity. They are the nocturnally periodic, nocturnally subperiodic and diurnally subperiodic forms. The susceptibility of a mosquito species to filarial infection depends on various factors, which could be genetic, physiological or physical. Survival analysis of Culex quinquefasciatus infected with W. bancrofti showed that the parasite load in the mosquito is a risk factor of vector survival. The extrinsic life cycle of the parasite is initiated when the mf are ingested by a mosquito vector during feeding on the host blood. On maturity, most of the infective L3 stage larvae migrate to the head and proboscis of the mosquito to get transmitted to the mammalian host during subsequent feeding. They develop to the adult L5 stage and the period of development and the longevity of the parasites varies according to the species of the nematode and the mammalian host. The rate of production of mf by the adult female was found to be stable at least for a period of five years. The life span of the mf has some influence on the dynamics of transmission of filariasis. Recent studies show that the endosymbiont, Wolbachia, plays an important role in the survival of filarial parasites. The possibility of in vitro and in vivo culture of filarial parasites is also reviewed.

Vaccination with 73kDa recombinant heavy chain myosin generates high level of protection against Brugia malayi challenge in jird and mastomys models

We have earlier reported identification, expression and purification of a 2.0kb cDNA clone coding for Brugia malayi heavy chain myosin which exhibited strong immuno-reactivity with bancroftian sera from endemic normal (EN) human subjects which are considered to be putatively immune. In the present study, immunoprophylactic characterization of B. malayi recombinant myosin was carried out in rodent models and the protective efficacy was evaluated by assessing the microfilarial burden and adult worm counts in vaccinated host after an infective larval challenge. Data indicates that immunization resulted in to a significant reduction in microfilarial burden (approximately 76%) and adult worm establishment (54-58%), accompanied with embryostatic effect (70-75%) in both the animal models. The findings suggest that immune-protection by recombinant myosin was conferred through both humoral and cellular arms of immunity as indicated by an increased antibody titer with predominance of IgG2a and IgG2b isotypes along with elevated level of IgG1 apart from significant proliferation of lymphocytes, increased nitric oxide production and profound adherence of splenocytes causing cytotoxicity to microfilariae and infective larvae. The present study indicates that the recombinant B. malayi myosin is a promising vaccine candidate against human lymphatic filarial infection.

Wuchereria bancrofti: Effect of single and multiple larval inoculations on infection dynamics and development of clinical manifestations in non-human primate Presbytis entellus

We earlier reported the successful experimental transmission of Wuchereria bancrofti from humans to the Indian leaf monkey (Presbytis entellus) [Misra, S., Tyagi, K., Chatterjee, R.K., 1997. Experimental transmission of nocturnally periodic Wuchereria bancrofti to Indian leaf monkey (Presbytis entellus). Experimental Parasitology 86,155-157.; Dube, A., Murthy, P.K., Puri, S.K., Misra-Bhattacharya, S., 2004. Presbytis entellus: a primate model for parasitic disease research. Trends in Parasitology 20(8), 358-360.] using a small number of animals. The present study, involving 27 langur monkeys, found the development of pathological manifestations ranging from filarial fever, lymphangitis, lymphadenitis, hydrocoele, and limb edema to minor histopathological changes in tissues after single, double, triple, or multiple inoculations of infective larvae of W. bancrofti recovered from Culex quinquefasciatus fed on human microfilaraemic blood. Thirty-eight percent of the infected langurs developed detectable microfilaraemia in their blood. Single or double larval exposure resulted in better worm establishment than multiple exposures with small numbers of larvae. All of the langurs receiving a single large inoculum and 85.71% of those receiving two inoculations harbored adult parasites. Worm establishment decreased with increasing number of larval inoculations. In all, 60% of infected langurs developed classical gross-pathological symptoms of lymphatic filariasis. Of these, 29.16% developed thickening of the lymphatics, 25% suffered from periodic rise in rectal temperature, and 16.66% developed scrotal swelling with presence of microfilariae in the hydrocoele fluid. Only one out of 25 langurs (4%) developed acute limb edema. It appeared that a single inoculum of a large number of infective larvae was able to induce maximum pathology. Fifty-six percent of the infected langurs acquired a peculiar sitting posture, retracting both the hind limbs, usually after 4-5 months of larval inoculation and eventually resulting in reduced mobility. Oral administration of diethylcarbamazine (citrate) at 12mg/kg for 12 consecutive days to one langur caused 80% suppression in microfilaraemia on day 8, killing all the adult parasites. Of the two immunosuppressed (cortisone- or prednisolone-treated) male rhesus monkeys included in the study, neither developed any of the above lymphatic symptoms or parasites after receiving larval inoculations on two or three occasions; however, a rise in rectal temperature in one of the animals was noticed. The present study thus reveals that the Indian leaf monkey, P. entellus, may serve as an ideal non-human primate model of human bancroftian filariasis for carrying out longitudinal studies on pathology, host-parasite interactions, and preclinical evaluation of candidate anti-filarial drugs or vaccines.

Variations in microfilariae and infective stages of two types of Wuchereria bancrofti from the Thai-Myanmar border

Comparative morphometric and morphological studies of microfilariae and infective stages were undertaken in nocturnally periodic and subperiodic Wuchereria bancrofti. For microfilariae, the body dimensions of nocturnally periodic (NP) were significantly smaller than nocturnally subperiodic (NSP), i.e. body length 268.03 ± 14.75 μm (NP), 307.61 ± 11.52 μm (NSP); cephalic space length 4.21 ± 0.62 μm (NP), 5.32 ± 0.79 μm (NSP); head to nerve ring 49.39 ± 5.43 μm (NP), 57.40 ± 4.46 μm (NSP); innenkörper length 33.05 ± 5.89 μm (NP), 44.02 ± 8.71 μm (NSP); cephalic space width 4.28 ± 0.59 μm (NP), 6.04 ± 0.68 μm (NSP); body width at nerve ring 5.01 ± 0.57 μm (NP), 7.45 ± 0.75 μm (NSP). The number of nuclei between the cephalic space and nerve ring of NP (66.67 ± 5.19) was also significantly less than in NSP (94.74 ± 6.95). For infective stages, the body dimensions of NP were significantly smaller than NSP, i.e. body length 1632.50 ± 131.48 μm (NP), 2002.63 ± 222.60 μm (NSP); head to nerve ring 103.09 ± 7.47 μm (NP), 122.44 ± 9.62 μm (NSP); head to oesophago-intestinal junction 567.69 ± 94.84 μm (NP), 666.75 ± 110.08 μm (NSP); body width at oesophago-intestinal junction 23.15 ± 1.55 μm (NP), 26.78 ± 1.62 μm (NSP). It is too early to infer the NP type as an additional sibling species of W. bancrofti but it is reasonable to treat it as a new variety and additional work is needed to clarify its status.

Immune responses in normal Indian langur monkeys (Presbytis entellus)--a primate model for visceral leishmaniasis

The Indian langur monkey (Presbytis entellus) is an experimental host for a range of human diseases and for the assessment of vaccine candidate antigens to some common parasitic infections. This experimental host is particularly suitable for the follow-up of immunological responses. To understand some of the mechanism that underlies the defense against experimental pathogens there is a need of the basic knowledge on antibody and cell mediated immune responses. In the present study 25 naïve monkeys were subjected to for assessment of their antibody responses to various human parasitic antigens as well as mitogen induced cellular responses. Only few monkeys were found to have low titer of antiparasitic antibodies. There was compressive dose dependent proliferative response of peripheral blood mononuclear cells. Unlike humans, the blastogenic as well as cytokine responses (IFN-gamma, IL-2 and IL-4) to Con A was considerably higher as compared to PHA. These findings are similar to what have been reported in other non-human primates, confirming the appropriateness of Indian langurs for pre-clinical trials.

Cellular immune responses of filaria (Litomosoides sigmodontis) infected BALB/c mice detected on the level of cytokine transcription

Cellular immune responses of BALB/c mice infected with 80 or 160 L3 of Litomosoides sigmodontis were studied over a period of 200 days postinfection (p.i.) by stimulating spleen cells with specific microfilariae and adult antigens and Concanavalin A (Con A). Effects were determined as the level of transcription of cytokine genes [interleukin (IL)-2, interferon (IFN)-gamma, IL-4, IL-5, IL-10, IL-13] employing a semiquantitative reverse transcriptase-polymerase chain reaction technique. Con A stimulation resulted in generally enhanced transcription levels in infected animals. Exposure to filarial antigens stimulated T cells of infected animals dependent on time p.i. There was a general strong response in the early prepatency (24 days p.i.), a temporary almost complete downregulation of cytokine gene transcription except IL-10 towards the end of prepatency (45 days p.i.), and subsequently strong reactions particularly concerning IFN-gamma and IL-13 during patency and postpatency. The dose of infection as well as the mode of antigenic stimulation had generally only small effects on the cytokine gene transcription: following the same type of kinetics, infection with 160 L3 as well as the use of microfilarial antigen generally induced lower levels of cytokine gene transcription compared with infection with 80 L3 and stimulation with female antigen, respectively.