Showing papers in "Transactions of The Royal Society of Tropical Medicine and Hygiene in 1971"

Evidence for cyclic development and short-lived maturity in the gametocytes of Plasmodium falciparum.

Abstract: 1 1 In a previous paper (Hawking et al, 1968) it has been shown that with malaria parasites exhibiting a periodic synchronous asexual cycle (eg Plasmodium knowlesi; P cynomolgie and P cathemerium), the gametocytes show a 24 or 48 hour rhythm in their development to maturity and that this maturity is short lived (6–12 hours) 2 2 In the present work, exflagellation of the male gametocytes of Plasmodium falciparum was studied quantitatively in 4-hourly blood films taken from 5 infected children in Gambia, West Africa 3 3 In 2 cases there was clear evidence of a 48 hour cycle in the number of exflagellations observed; in 2 cases there was a “probable” cycle present, and in 1 case there was a “possible” cycle although the evidence is not decisive 4 4 It is concluded that the gametocytes of P falciparum probably resemble those of other periodic plasmodia in showing a (48 hour) rhythm of development to maturity (taking into account the well known irregularity of P falciparum) 5 5 The development of gametocytes of P falciparum was also studied in Aotus monkeys The classical view was confirmed that development from the merozoite takes more than 9 days and that there is no evidence for cell division during this process

The life cycle of the coccidian parasite, Toxoplasma gondii, in the domestic cat

Abstract: Earlier work in which the coccidian nature of the protozoan parasite Toxoplasma gondii was revealed has been confirmed and extended in a series of experiments using only specific pathogen free (SPF) cats. All of these cats, prior to our experiments, were negative for both Coccidia and Toxoplasma. Experiments on 17 of these cats are described. 10 were fed with mouse brains containing tissue cysts of Toxoplasma. 8 of these shed Toxoplasma oocysts in their faeces within 5 to 10 days of infection. 2 cats had shed no oocysts before they were killed on the 3rd and 4th day after infection. 5 cats were fed with Toxoplasma oocysts but gametogonic development resulting in the production of oocysts was observed in only 1 individual; oocysts appeared in the faeces 9 days after the infective meal. 2 cats were examined as controls; 1 received no addition to its diet, the other was fed “negative” brains. Neither showed any evidence of infection. Examination of the gut of infected cats showed that shizogonic and gametogonic stages develop usually in the ileum although the entire length of the small intestine can be affected. The parasites were observed in the epithelium of the tips of the villi, developing within vacuoles, and lying between the nucleus and brush border of the cell. All stages of schizogony and gametogony may be found together, occurring in no particular sequence along the epithelium of the villus; multiple infections of the host cells are common. Schizonts are characterized by granular, basophil cytoplasm and vesicular, karyosomic, Feulgen-negative nuclei which become dense and Feulgen-positive when merozoite formation takes place. The merozoites vary from 4 to 29 per schizont and measure 3·5-4·5μ by 1μ in sections; in smears their dimensions are 4·9 (SD = 1·0)μ by 1·5μ. They form clusters about a residual body and may appear to radiate fan-wise from it in sections. The microgametocyte is spherical, about 10μ in diameter and gives rise to 12–32 microgametes which form on its surface, are slender and crescentic and about 3μ in length, excluding the flagella. The macrogametocyte has, throughout development, a vesicular, karyosomic and Feulgen-negative nucleus. At the commencement of development, the cytoplasm contains many basophil and few PAS-positive granules; at its completion this condition is reversed. No granules were seen to be associated with the formation of the oocyst wall. The oocyst itself measures 12·7 (SD = 0·7)μ by 10·4 (SD = 0·8)μ. Sporulation, which does not occur within the gut of the cat, gives sporocysts measuring 7·8 (SD = 0·9)μ by 6 (SD = 0·5)μ. These coccidian stages of Toxoplasma are compared and contrasted with those of Isospora spp. of the cat. Despite its significant resemblances to Isospora, the retention of the existing nomenclature of Toxoplasma gondii is supported.

Studies of the epidemiology of arthropod-borne virus infections at Mitchell River Mission, Cape York Peninsula, North Queensland. IV. Arbovirus infections of mosquitoes and mammals, 1967-1969.

Abstract: 19 strains of 6 viruses (Kunjin, Kokobera, MRM3929, Koongol, Kowanyama and MRM3630) were isolated from 40,508 mosquitoes collected on 8 occasions from March 1963 to November 1966, at Mitchell River Mission in Cape York Peninsula, Queensland. Isolation rates were lower than in earlier collections in the same area, varied markedly between years, and were very low in each dry season (October–November) when only 4 strains were isolated, all from Anopheline mosquitoes. One virus isolated, Kowanyama, appears to be unrelated to all agents with which it has been compared; one, MRM3630, is related to but easily distinguishable from Mapputta virus; one, MRM3929, was previously isolated from a bird from the same area, but the isolation reported is the first from mosquitoes. Serological tests of children and domestic fowls gave supporting evidence of the occurrence of infections with Group B arboviruses, and also demonstrated infections with Sindbis and Ross River virus. The findings do not indicate the mode of survival of arboviruses in the markedly seasonal environment in this area.

Comparison of a counting chamber and thick smear methods of counting microfilariae

Abstract: A glass chamber method of counting living microfilariae in 20–100 c.mm. samples of freshly haemolyzed blood proved to be substantially more sensitive than, and as reliable as, the use of standard wet or stained dry films. The method has the further advantages of simplicity and brevity. The results showed that with the “normal” thick smear technique between 30 and 40% of microfilariae are lost during processing of the slide. It is suggested that the chamber counting method has practical field and laboratory utility.

Serum antibody in acquired malarial immunity.

Abstract: The influence of specific immunity upon the course of infection may vary considerably with different species of plasmodia and different mammalian hosts harbouring the same species of parasite. Certain infections, for example P. knowlesi in rhesus monkeys, lead to a rapidly progressive parasitaemia and almost inevitably to a fatal outcome so that the immune response is ineffective unless animals are protected initially by drug therapy. In other instances, including many examples of primate and avian malaria, infection is followed by clinical immunity associated with continuing low-grade infection, occasional parasitaemia and relapse after splenectomy. This 'non-sterilizing' response was analysed in detail by SERGENT (1963) and called "premunition". Finally, certain infections, such as P. berghei in the rat and P. cynomolgi bastianellii in man, produce a parasitaemia of comparatively short duration followed by long-lasting specific resistance during which no living organisms can be demonstrated by sub-inoculation or following splenectomy; after challenge of such immune individuals, parasites are rapidly killed--usually within about 2 days. This type of response has been referred to as 'sterilizing' immunity. The occurrence of these diverse responses to specific malarial infections implies that our present knowledge of the underlying immune mechanisms, which is restricted to a limited number of host-parasite combinations, is probably not applicable to all malarial infections.

The effects of some immunosuppressive agents in experimental chronic Chagas's disease☆

Abstract: The effects of some immunosuppressive agents (gamma radiation, cyclophosphamide, Imuran and 6-mercaptopurine) administered, in the course of chronic Chagas's disease, to mice experimentally inoculated with different strains of Trypanosoma cruzi, have been studied Gamma radiation and cyclophosphamide could induce, in mice inoculated with the “CL” strain, a fresh acute phase with outbreaks of high parasitaemia and a high mortality rate, whereas no increase of parasitaemia has been observed in animals inoculated with strains “Y,” “Berenice” and “PNM” and similarly treated during the chronic phase Imuran and 6-mercaptopurine were not able to alter the course of experimental chronic Chagas's disease Some factors accounting for the differences observed in animals inoculated with different strains of T cruzi and submitted to immunosuppressive agents have been discussed

Control of schistosomiasis mansoni in a small north east Brazilian community.

Abstract: A seven-year project for the control of schistosomiasis due to S. mansoni was launched in November 1960 in the small village of Pontezinha, county of Cabo, state of Pernambuco. Control measures were limited to environmental sanitation and a community health education programme. Human infection rates were progressively reduced in the project area. Surveys made in 1967 and 1968 show that a successful degree of control of schistosomiasis has been achieved in the project area. Studies on snail population dynamics and on natural infection of small mammals captured in the area were made. The average monthly cost of the project was US $1,402·00, or an equivalent of US $0·98 per month per protected person.

Pathological effects of Trypanosoma brucei on small blood vessels in rabbit ear-chambers

Abstract: The effect of Trypanosoma brucei infection on small blood vessels has been studied in regenerative ear-chambers in rabbits. Damage to the vessels was observed about 2 weeks after the animals had been inoculated with trypanosomes. Mononuclear phagocytic cells collected on the endothelium of the small venules, the blood flow was obstructed and the vessels disintegrated. Fibroblasts and collagen in the connective tissue degenerated. Few trypanosomes were present in the circulating blood but the tissue spaces contained many parasites. From time to time the trypanosomes in the tissue spaces were trapped and digested by phagocytes.

The diagnostic and prognostic significance of the serum enzyme changes in heatstroke

Abstract: Serum transaminase (SGOT, SGPT), lactic dehydrogenase (LDH) and creatine phosphokinase (CPK) levels were measured serially in 84 Bantu gold-miners with a provisional diagnosis of heatstroke. In 75 patients proved to have heatstroke, SGOT levels were invariably, and SGPT, LDH and CPK values almost invariably, elevated within 24 hours of admission. The levels continued to rise for approximately 48 hours and remained elevated for average periods of 12 to 14 days. In the patients who proved to have acute infections, SGOT, SGPT and LDH values were normal. The serum enzyme changes were therefore useful in confirming or excluding the diagnosis of heatstroke. The degree of elevation of the enzyme levels was also a reliable index of the severity of tissue damage in heatstroke and hence the patient's likely outcome. In 15 patients in whom the SGOT level exceeded 1,000 units in the first 24 hours, renal, hepatic and cerebral damage tended to be severe, and death or permanent sequelae were common. In 20 patients with SGOT values of less than 1,000 units, the tissue injury was usually mild or moderate and completely reversible, and there was only 1 death.

The effect of immuno-depression due to neonatal thymectomy on infections with trypanosoma cruzi in mice

Abstract: Neonatally thymectomized C3H or Rockland mice infected with trypanomastigotes of Trypanosoma cruzi had higher parasitaemia and shorter survival than their non-thymectomized counterparts. The appearance of antibodies detectable by IFT, IHA or DAT was delayed in neonatally thymectomized mice infected with epimastigotes of T. cruzi. Less thymectomized than non-thymectomized mice survived infection with epimastigotes. Our findings suggest that thymus-dependent, immune mechanisms are involved in controlling infection with T. cruzi in mice.

A shellfish-borne cholera outbreak in Malaysia

Abstract: 11,650 specimens were studied bacteriologically. 139 El Tor Inaba strains were isolated from the stool of suspected patients and contacts, from water of various wells and tributaries of Kelantan river, and from shellfish. 15 El Tor Inaba, 25 non-agglutinable and 10 partially-agglutinable and auto-agglutinable (rough) strains were demonstrated in edible types of shellfish. 55 non-agglutinable vibrios were isolated from stools of suspected patients, from shellfish and water, and were regarded as pathogenic. Shellfish and water were considered as predominant vehicles for the transmission of cholera in this outbreak. The short-term carrier state is emphasized and the causal relationship of cholera with carrier was found to be insignificant in this outbreak. Bacteriological significance of partially-agglutinable and auto-agglutinable (rough) El Tor vibrios is discussed.

Studies on transmission of bancroftian filariasis in North-eastern Tanzania

Abstract: The relative importance of the 3 known vectors of Bancroftian filariasis in East Africa was evaluated on an annual basis at 3 contrasting localities in north-eastern Tanzania. In the urban parts of Tanga, a coastal town, the only significant filariasis vector was C. p. fatigans . This mosquito was responsible for about 10,000 bites per person per annum, with an infectivity rate of about 0·23%. In the rural district around Muheza, some distance inland, all 3 filariasis vectors were active. Their annual mean biting densities per person at the village of Ubwari were 1,591 A. funestus , 2,971 A. gambiae A. and 3,058 C. fatigans , with calculated infectivity rates of 6·1%, 2·4% and 0·54% respectively. The third locality, further inland at Gonja Maore, receives only about two-thirds as much rainfall annually as do Tanga and Muheza. At Gonja, A. funestus and A. gambiae (mainly species B) were found to be filariasis vectors, with annual mean biting densities of 1,250 A. funestus and 5,963 A. gambiae per person, and infectivity rates of 3·5% and 0·9%. Densities of C. fatigans at Gonja averaged 3,603 bites per person per annum, but infective filarial larvae were not observed in any of 360 specimens dissected. From these data it was calculated that during 1969 the mean personal exposure to the risk of infection with 3rd-stage larvae of Wuchereria bancrofti was due to the bites of 23 ± 15 infective mosquitoes at Tanga, to the bites of 185 ± 84 infective mosquitoes at Muheza Ubwari and to the bites of 95 ± 66 infective mosquitoes at Gonja Maore. The apparent risks of filariasis transmission at Muheza were due 52% to A. funestus , 40% to A. gambiae A. and 8% to C. fatigans . At Gonja the risks of transmission were due 46% to A. funestus and 54% to A. gambiae (principally species B). These data are discussed. Finally it is pointed out that although the anopheline vectors of filariasis in rural areas present an intractable problem, it should be relatively easy to reduce risks of filariasis transmission in urban areas through control of C. fatigans .

The effects of cordycepin on malaria parasites

Abstract: 1. 1. The effects of cordycepin (3′-deoxyadenosine) both on cultures of the erythrocytic stages of Plasmodium knowlesi incubated in vitro and Plasmodium berghei berghei in vivo have been studied. 2. 2. Concentrations of drug as low as 106M affected the growth in vitro of the parasite after a lag period of about 4 hours. These effects could be partially prevented by adenosine but not by other purines tested. 3. 3. Of the various anabolic and catabolic processes studied in the malaria parasite in vitro, the drug affected nucleic acid synthesis first and to the greatest extent. 4. 4. It was without observable effect on the host red cell. 5. 5. Cordycepin was therapeutically active at doses of 50 mg./kg. and above against blood-induced P. b. berghei infections. Complete cure was not obtained even at the highest doses and toxic effects were observed at doses of 200 mg./kg. and above.

An amastigote phase of the sleeping sickness trypanosome

Abstract: 1. 1. We have found amastigotes closely packed together with “white thrombus” in capillaries, in sections of the choroid plexus of rats which had been infected with a strain of Trypanosoma brucei isolated from man in Botswana. 2. 2. Amastigotes were found at 48 hours during the prepatent period, also when the infection was fully established after the relapse. 3. 3. Amastigotes and sphaeromastigotes, also trypomastigotes in different stages of “unrolling” were found in smears of the choroid plexus. 4. 4. Similar forms in smears of other organs tended to show signs of degeneration. 5. 5. We believe that the choroid plexus is an important, probably the most important site of formation of an occult visceral phase of the sleeping sickness trypanosome.

The occult visceral phase of mammalian trypanosomes with special reference to the life cycle of Trypanosoma (Trypanozoon) Brucei

Abstract: 1. 1. We have reviewed the indirect evidence for suspecting the existence of an occult visceral phase in Trypanosoma (Trypanozoon) brucei . This evidence consists of:— 1.1. a) Inoculated trypomastigotes of Botswana strains (unlike “laboratory strains” adapted to rats) do not begin to divide and multiply immediately they reach the blood; neither do their numbers affect the height of infection nor the length of prepatent period. They are removed from circulation and are replaced by a new population with different morphology and behaviour. 1.2. b) This new population consists of agranular trypomastigotes which are flushed into the blood at 72 hours; they do not divide until they have been in the blood for some hours. 1.3. c) Trypomastigotes of the first flush (72 hours) and of the relapse (192 hours) we call “long-narrow” forms, they are succeeded by “long-flat” forms which are also agranular under phase contrast, but undergo binary fission. 1.4. d) The long-flat forms develop granules and are removed from the blood. 1.5. e) Multinucleate forms are seen occasionally in the peripheral circulation but their numbers are increased by immuno-suppression, they are also found in smears of internal organs. 1.6. f) Amastigotes and sphaeromastigotes (the “latent bodies” of earlier workers) have been seen in smears of internal organs; most of them show signs of degeneration. 1.7. g) The evidence of headache and associated hydrocephalus in sleeping sickness, also the swelling of the choroid plexus in experimentally infected rats, is reviewed. 2. 2. We have also reviewed the direct evidence of occult stages in different species of the genus Trypanosoma . In all subgenera of mammalian trypanosomes, with the exception of Duttonella and Nannomonas , amastigote and/or sphaeromastigote forms have been found. In Schizotrypanum these forms are intracellular, in Herpetomonas and Megatrypanum they are intravascular. In Trypanosoma (Trypanozoon) brucei the amastigote forms are found in large masses in the choroid plexus. 3. 3. We have proposed, as a working hypothesis, the life cycle shown in Fig. 3 for T. brucei in the vertebrate host. On this hypothesis we base our explanation of the synchronism of the initial infection and of the remission, also our view of the fundamental difference between Rhodesian and Gambian strains. 4. 4. In conclusion, we have discussed the following points:— 1. a) We think that the choroid plexus is the most important but not necessarily the only site for the formation of an occult phase in T. brucei infection; the lung is also a candidate. 2. b) Penetration of the cerebrospinal fluid by the trypanosome is probably not related to the occult phase. 3. c) The secretion of antigen by the granular forms and the massive response of antibody that it elicits might inhibit cell mediated immunity against the amastigote phase. 4. d) Existing chemotherapeutic agents are probably active against the occult visceral phase of T. brucei , but this question needs to be investigated specifically.

The distribution of Toxocara larvae in the central nervous system of the mouse.

Abstract: The distribution of T. canis and T. cati larvae in the brains of experimentally infected mice were examined. Larvae were found within the brains of all mice infected with the former species, whereas, they were present in only 8·3% of those infected with the latter. The larvae of T. canis showed a predilection for the cerebellum, more per unit weight of tissue being found in this region than in either the cerebral hemispheres or the brain-stem. A few mice also contained larvae within the spinal cord. The incidence of eye involvement was 4·5%.

Epidemiology of tropical nutritional neuropathy in Nigerians

Abstract: Nigerian nutritional ataxic neuropathy comprises panmyelopathy, bilateral optic atrophy, sensorineural deafness and polyneuropathy. In a third of the patients, mucocutaneous evidence of malnutrition is present. The disease occurs in high prevalence in the areas of Nigeria where cassava is most intensely cultivated. Cassava contains a cyanogenetic glycoside, from which hydrocyanic acid is released on hydrolysis. The sex incidence is equal. It is a disease of the poor who subsist entirely on culinary derivatives of cassava. It has a peak prevalence in the 4th to 6th decades. In 41% of 320 patients studied, a positive history that someone else in the household or family suffered from the disease was obtained. In familial cases, 50% are conjugal. There is biochemical evidence of increased exposure to cyanide in ataxic families. There is no evidence so far of a genetically determined predisposition to the disease. Field surveys in 2 villages in an endemic area, and one village in a non-endemic area, showed a positive correlation between the prevalence of the disease and consumption of cassava meals and biochemical evidence of chronic cyanide intoxication. The prevalence rate of the disease in the endemic foci is 18 to 26 per thousand of the population, with a peak prevalence rate of 80 per 1000 in the 6th decade. Cassava processors and farmers who grow and handle cassava may be at special risk. Goitre is not uncommon in patients and may be related to inhibition of iodine uptake by the thyroid due to high concentration of plasma thiocyanate (a detoxication product of cyanide). The epidemiological data support the hypothesis that in Nigerians, chronic cyanide intoxication of dietary origin is the most important factor in the aetiology of ataxic neuropathy. The main source of the cyanide is cassava.

Malaria and the tropical splenomegaly syndrome in New Guinea

Abstract: The pattern of malarial parasitaemia and the incidence and degree of splenomegaly have been studied in the population of the Upper Watut Valley in New Guinea. Malaria is the only apparent cause of splenomegaly found in this area, and all cases of gross splenomegaly in adults conform to the descriptions of the tropical splenomegaly syndrome. Malaria is meso-endemic and moderately stable. The incidence of parasitaemia is similar in villages at 3300 feet and 5200 feet above sea level, although the incidence of splenomegaly in adults is lower at the higher altitude. Peak parasitaemia is recorded at 3 years of age and then declines slowly, and parasite rates are significantly lower in adult subjects with splenomegaly than in those without palpable spleens. No difference in distribution of species of plasmodia was found between individuals with different grades of splenomegaly or in different age groups or at different altitudes. P. vivax was the predominant species in all groups.

A membrane feeding technique for the infection of Culicoides nubeculosus mg. and Culicoides variipennis sonorensis coq. with Onchocerca cervicalis Rail. and Henry

Abstract: The transmission of Onchocerca cervicalis Rail. and Henry in the horse is being investigated at Winches Farm Field Station, St. Albans. Laboratory colonies of Culicoides nubeculosus Mg., the natural vector of O. cervicalis in Europe, and of C. variipennis sonorensis Coq., a North American midge, have been established. A technique has been developed to facilitate the artificial infection of these midges with O. cervicalis. Experimental flies imbibed a meal of O. cervicalis microfilariae suspended in defibrinated ox blood at 38°C. A plucked skin from a one-day-old chick was used as a membrane. 232 C. nubeculosus and 117 C. v. sonorensis were fed and 5·5% of the C. nubeculosus and 7·7% of the C. v. sonorensis subsequently developed infective (3rd stage) larvae. The fact that 3rd stage larvae developed in specimens of C. v. sonorensis is a point of special interest because this midge has not yet been identified as a vector of O. cervicalis.

Immunoglobulin levels in the Kaiapit and upper Watut areas of New Guinea: with special reference to the tropical splenomegaly syndrome

Abstract: Serum concentrations of IgA, IgG and IgM were estimated for 2,000 inhabitants of 2 malarious areas of New Guinea—Kaiapit, where spleen rates are high in children but splenomegaly occurs infrequently in adults and is never gross, and the Upper Watut Valley, where the tropical splenomegaly syndrome is particularly common, and 80% of adults and children have palpable spleens. Kaiapit adults had significantly higher IgM levels than children: IgM levels tended to increase throughout life, were higher in women than in men and in adults with splenomegaly. IgG and IgA levels showed no significant relation to increasing age above 10 years, to sex or to the presence or absence of splenomegaly. The youngest Watut children had higher IgM levels than Kaiapit subjects. IgM concentrations rose more rapidly with age, particularly in the first 20 years of life, so that the mean Watut adult level was more than twice that of Kaiapit adults. In Watut children splenomegaly was associated with significantly higher levels of all 3 immunoglobulin fractions, whereas adults with splenomegaly showed markedly higher levels of IgM, but significantly lower IgA concentrations than did subjects with impalpable spleens. The change in the pattern of immunoglobulin levels in association with splenomegaly occurred between the ages of 6 and 20 years, indicating that the transition from simple malarious splenomegaly to tropical splenomegaly syndrome probably occurs at this age. Subjects living near the valley floor had higher spleen rates than those living in high villages; IgM concentrations were also affected by altitude. The reason for this remains obscure, but it is suggested that both observations may be related to differences in intensity of operation of the factors responsible for the development of the tropical splenomegaly syndrome.

Bleeding in louse-borne relapsing fever I. Clinical studies in 37 patients

Abstract: 37 patients with louse-borne relapsing fever (LBRF) were investigated. In 21 there was evidence of bleeding. Thrombocytopenia, with platelelet counts below 150,000/c.mm., was found in 31 (84%). This was attributed to increased consumption due to intravascular clotting and to pooling in the enlarged spleen. There was a significant correlation between bleeding and duration of illness, platelet count and SGOT. 7 out of 10 patients with prolonged prothrombin (PT) and partial thromboplastin times (PTT) and evidence of severe hepato-cellular damage, had epistaxis and purpura. Plasma fibrinogen levels were raised in 29 patients. Death of 1 patient who had hypo-fibrinogenaemia was attributed to DIC.

Mosquitoes of british honduras, with some comments on malaria, and on arbovirus antibodies in man and equines

Abstract: A survey in 1967 of mosquitoes taken by human bait and trap catches in British Honduras along a transect from the coast near Belize City to riverine terrain and upland forest 45 miles inland yielded 65 species— Chagasia (1), Anopheles (8), Trichoprosopon (2), Wyeomyia (5), Limatus (2), Sabethes (2), Mansonia (2), Coquillettidia (2), Uranotaenia (5), Aedomyia (1), Psorophora (8), Aedes (9), Haemagogus (2), Culex (15), Deinocerites (1). Mosquito densities are very low in the dry season (April–May), rapidly increasing with the main rains which begin about late May–June, and continuing probably considerable until the following April–May dry season. Diurnal, crepuscular and nocturnal activity, and vertical distribution in forest, resembled findings from elsewhere in Middle America. The coastal pest, Aedes taeniorhynchus , occurred in small numbers as far inland as 45 miles. The Aedes terrens group includes a new species, Ae. bertrami Schick 1970. Mansonia dyari and Ae. cozumelensis first described, respectively, from Jamaica in 1970 and from the Yucatan in Mexico in 1966, were taken, and also Ae. vexans , common in North America. Differentiation within C. (Mel.) opisthopus/taeniopus is still inconclusive, available larvae and ♂ genitalia being assigned to C. (Mel.) n. sp. near paracrybda. Ae. aegypti was not found, following an eradication programme. The anopheline and culicine species include, respectively, vectors of malaria and of arboviruses. As a result of a malaria eradication campaign, few cases of malaria occur. In 1967, equines had VEE antibodies and VEE virus was isolated, by other workers, in sentinel hamsters near Belize City but the human population which showed NT-antibodies to VEE, SLE and Ilheus appears on the whole to have escaped any major infections, in recent years. There was no conclusive evidence for arbovirus infections of British garrison troops. Up to early October 1971, British Honduras escaped, although several competent vectors occur, the severe wave of epizootic VEE in equines, with also human cases, which occurred in other Central American countries from 1969 to September 1971. In 1969 and, particularly in 1971, precautions were taken by vaccination of horses in a buffer zone along the borders of the adjacent, and severely affected, territories of Mexico and Guatemala.