The leaf-monkeys, Presbytis cristata and Presbytis melalophos, experimentally infected with subperiodic Brugia malayi, have been used for studies on the pathoimmunology of the infection and the screening of potential filaricides during the last 6-8 years, and considerable information on the pattern of microfilaraemia and adult worm recoveries have been obtained. The prepatent periods in 97 P. cristata and 45 P. melalophos, each infected with about 200 infective larvae, were similar, these being approximately 70 and 68 days respectively. Although all infected animals became microfilaraemic, the peak geometric mean count was much higher in P. cristata than in P. melalophos, this being 182.0 and 65.8 per ml blood respectively. Mean adult worm recovery expressed as the percentage of the infective dose was 4.7% and 2.5%, respectively. Most worms were recovered from the sacral nodes/thoracic duct or inguinal lymph nodes in these animals. In view of the higher worm recovery and the higher peak microfilaraemia attained, it is concluded that P. cristata is a better model for the infection than P. melalophos.
The dynamics of the transmission of subperiodic Brugia malayi in a typical endemic area in Malaysia was studied over a period of 4 years. Mass chemotherapeutic control with diethylcarbamazine citrate was found to be inefficient, new cases being detected even after the fifth treatment cycle of 6 mg/kg X 6 days per cycle. This is in marked contrast to the situation in periodic b. malayi areas where mass treatment efficiently controlled the infection. The disparity in results in these two areas is attributed to zoonotic transmission of subperiodic B. malayi from non-human primates where a mean infection rate of 76.3% was found.
An estimated 13 million people in the Oriental Region have brugian filariasis. The filarial parasites that cause this disease exist in periodic and sub-periodic forms and are transmitted by four genera of mosquito: Anopheles, Mansonia and, less frequently, Coquillettidia and Ochlerotatus. In most endemic countries, control of the disease has been entirely based on chemotherapy, although house-spraying and use of insecticide-treated bednets can be quite effective against the vectors of nocturnally periodic Brugia malayi and B. timori. The vector-control methods that may be applied against the Mansonia mosquitoes that transmit the parasites causing sub-periodic brugian filariasis are reviewed here. Most of the conventional methods for controlling the immature, aquatic stages of mosquitoes have proved unsatisfactory against Mansonia. The reason is that, unlike the those of other genera, the larvae and pupae of Mansonia spp. are relatively immobile and obtain air not at the water surface but from the underwater roots, stems and leaves of floating plants to which the larvae and pupae attach. Removal of host plants can be very effective in reducing Mansonia productivity, whereas large-scale use of herbicides is restricted by the potential adverse effects on the ecosystem. Environmental management in water-development projects remains the best option.
Field observations were made on Coquillettidia crassipes during a study of Mansonia in a swamp forest ecotype in Tanjong Karang. There was an increase in abundance in July consistent with the increase in abundance of Mansonia and an increase in rainfall. The biting cycle showed a dramatic early peak during the period 1900-2000 hours. The probability of daily survival through one day for the first three gonotrophic cycles was 0.770, 0.722 and 0.759. Two of the 54 Cq. crassipes dissected were infective, with two and 25 L3 larvae of Brugia. Both subperiodic B. malayi and B. pahangi developed into L3 larvae in laboratory bred Cq. crassipes. The index of experimental infection was higher for B. pahangi. Mansonia bonneae and Ma. uniformis showed higher indices of experimental infection than Cq. crassipes for subperiodic B. malayi. It is concluded that in an endemic area with a high density of Cq. crassipes it could act as a secondary vector of Brugian filariasis.
Histochemical demonstration of acid phosphatase activity in microfilariae gives sufficiently characteristic and consistent results for the differentiation of even closely related species. No difference could be detected among nocturnally periodic, nocturnally subperiodic and diurnally subperiodic Brugia malayi, but they could readily be distinguished from B. pahangi. Similarly, Dirofilaria repens could be readily distinguished from D. immitis and B. booliati from B. sergenti. The enzyme distribution pattern of a Malaysian rural strain of Wuchereria bancrofti was different from those of other regions.
A comparative study of five periodic human strains of Brugia malayi, originating from India, China, Korea, Malaysia and Indonesia, is given. This morphological analysis is based on males; the "standard" characters (oesophagus, papillae, spicules...) appear identical. On the contrary, the cuticular ornamentation of the posterior region--which is composed of the area rugosa and of a system of bosses and constitutes a secondary non-skid copulatory apparatus--differs following the geographical origin of the strain. A key is given, based on this character. 1(2) At 800-1,200 micron from the tip of tail, numerous cuticular bosses present on the right side of the body (fig. 2 and 8 B). 2(1) At 800-1,200 micron from the tip of tail, cuticular bosses absent or scarce on the right side of the body (fig. 8 D). 3(4) At 1,800-1,200 micron from the tip of tail (fig. 4), scarce and slightly projecting cuticular bosses on the dorsal side of the body contrasting with well projecting lateral cuticular bosses (fig. 9 E and F). Anterior extremity of the area rugosa made by a few stripes of tiny bosses linked transversally (fig. 9 A). 4(3) At 1,800-2,200 micron, numerous cuticular bosses on the dorsal side of the body (figs. 5, 6 and 7). Anterior extremity of the area rugosa made by the stripes of longitudinal rods (fig. 9C). 5(6) Oblong transversally stretched cuticular bosses on the dorsal and left sides of the body, anteriorly to the area rugosa (fig. 5); big oblong bosses on the left side (fig. 9 B). Transversal wrinkles and stripes of rods absent on the dorsal side of the body. 6(5) Round cuticular bosses on the dorsal and left sides of the body anteriorly to the area rugosa (figs. 6 and 7): no big oblong bosses on the left side. Transversal wrinkles or stripes of rods present on the dorsal side of the body (fig. 9 D). Nomenclaturally, such differences could be used in defining different taxa, but it could be useful to perform "blind determination" (material without labelling), to study conveniently the morphology of microfilariae (often an excellent indication for speciation in that group of Nematodes) and, evenly, to proceed to parallel studies on isoenzymes. However, whatever could be the taxonomical conclusion, the differences observed in Brugia malayi originating from different regions appear to the sufficient to consider the existence of four distinct diseases.
Tropical pulmonary eosinophilia (TPE) is considered to be a variant of human filarial infection. The pulmonary manifestations of TPE have been well described. Extra-pulmonary features of the disease, although not commonly seen, have been reported previously. A 9-year-old Malay girl with a history of recurrent cough and wheezing was admitted because of cardiac failure. Physical examination revealed a very sick girl with tachypnoea, central cyanosis, finger clubbing, elevated jugular venous pulse, generalized crackles and rhonchi in the chest, a loud second heart sound and hepatosplenomegaly. A chest radiograph showed cardiomegaly and right pleural effusion. Laboratory investigations revealed hypochromic, microcytic anaemia with persistent blood eosinophilia (absolute eosinophil counts varied from 1.9 to 5.5 x 10(9)/1). The ELISA test for antifilarial IgG antibodies was strongly positive. She responded promptly to treatment with diethylcarbamazine. In summary, this is a patient with TPE who presented with cor pulmonale, probably due to late-stage interstitial pulmonary fibrosis. In order to prevent the long term morbidity of cardiorespiratory disability, the early signs of TPE should be recognized and the infection treated.
Sera from fifty subjects with different presentations of Brugian filariasis and from common soil-transmitted helminth infections were tested for specific anti-filarial IgG and its subclasses. Anti-filarial IgG, IgG1 and IgG3 showed cross-reactivities with soil-transmitted helminthic infections and no significant differences in optical densities among the various groups of filarial patients. In comparison with other groups of subjects, IgG4-ELISA of sera from microfilaraemic patients and some previously microfilaraemic patients showed a significant increase in optical density readings, while IgG2-ELISA showed elevated optical density readings in sera of patients with chronic elephantiasis. Therefore IgG2-ELISA is potentially useful in the diagnosis of brugian chronic elephantiasis while IgG4-ELISA may be beneficial for follow-up diagnosis of treated microfilaraemic patients.