Insecticide susceptibility of some vector fleas and mosquitoes in Burma.

Rat fleas and mosquitoes are insect vectors of public health importance in Burma. Plague is endemic in Central Burma and DDT has been the principal insecticide used for its control to date. Dengue haemorrhagic fever, recently introduced and transmitted by Aedes aegypti, has been spreading to major towns since 1971. The rodents, Rattus rattus, R. exulans, Bandicota bengalensis, Mus musculus, as well as shrews were commonly caught during routine trapping in the country. Rattus norvegicus, prevalent in Rangoon City, is not found in Central Burma. The rat fleas, Xenopsylla cheopis and X. astia, were found to be infesting these rodents, the former being the principal vector of plague. Insecticide susceptibility tests have been carried out periodically in plague endemic areas and Rangoon since 1966 and it is now observed that rat fleas in most of these endemic towns and Rangoon Port are no longer susceptible to DDT. Subsequent rechecks in towns where fleas became resistance to DDT show that fleas are persistently resistant to the insecticide. Aedes aegypti is found to be highly prevalent both in rural and urban areas of almost every major town and townships below 900 meters. Insecticide susceptible tests on this mosquito in limited areas show that the mosquito is generally resistant to DDT but susceptible to other insecticides. With the development of DDT resistance in fleas, it is now necessary to change to an effective insecticide in the control of plague in Burma.

Dengue haemorrhagic fever in Burma.

Although sporadic from 1965 to 1969, a major outbreak of dengue haemorrhagic fever (DHF) occurred for the first time in Rangoon in 1970. Since then the disease has occurred every year in Rangoon and is now observed to be expanding to other urban areas in the country. The clinical diagnosis of DHF was confused by concurrent outbreaks of influenza A in 1971 and influenza A and B in 1972. A laboratory study of 3,447 clinically diagnosed haemorrhagic fever cases showed that 1643 cases (47.8%) were due to dengue and chikungunya, 296 (8.6%) to influenza A, 85(2.5%) to influenza B, 12(0.3%) to measles and 1411(40.8%) were of unknown aetiology during the 5 year period 1970-1974. Ae. aegypti mosquitoes are widely distributed in the country up to and including 900 meters above sea level but breeding is not found above that altitude. The absolute larval population which is highest in July as well as landing rate correlated with the peak incidence of DHF cases.

Epidemiological features of skin diphtheria infection in Rangoon, Burma.

A survey for skin diphtheria was carried out on 493 patients with skin lesions who were attending Veneral Diseases & Dermatology Clinic in Rangoon in 1971. 63.8% of the patients had C. diphtheriae in their skin lesions. All ages and both sexes were equally affected. Skin lesions yielding C. diphtheriae on culture were indistinguishable from those associated with other bacteria including ecthyma, pyoderma and secondarily infected with parasitic infections. Out of 108 strains tested 18.5% were found to be toxigenic, mainly intermedius. No toxigenic gravis strain was encountered. No relation existed between the type of lesion and the type or toxigenicity of the infecting strain. 75% of these toxigenic strains were isolated from children under 5 years of age. The phage types of toxigenic strains isolated were: II-IV, XII, Ph r, 8, 19-20, III, IVII and IV.

Epidemiological features of dengue and chikungunya infections in Burma.

A serological survey for antibody to dengue and chikungunya was carried out in all 14 divisions and states and 2 border towns in Burma during 1973-74. Dengue HI antibody prevalence rate of less than 10% was observed in Arakan and Shan States, 10 to 30% in the Irrawaddy, Pegu, Mandalay Divisions and Kachin, Mon and Karen States, 31 to 60% in Sagaing Division, and over 60% in Rangoon, Magwe and Tenasserim Divisions. Similarly, chikungunya HI antibody prevalence rate of less than 10% was observed in Arakan State, 10 to 30% in the Irrawaddy, Pegu, Mandalay and Sagaing Divisions and Kachin State, 31 to 60% in Rangoon Division and Mon State. Both dengue and chikungunya antibodies were detected where Aedes aegypti mosquitoes were prevalent but the antibody prevalent rates were not directly proportional to the premises index. No HI antibody to dengue nor chikungunya was detected in Aedes aegypti free hilly areas, Chin and Kayah States, but was detected in the Shan State, Dengue and chikungunya infections were observed both in rural and urban populations. Dengue and chikungunya infections affected all socioeconomic classes in Rangoon equally but in Mandalay high socioeconomic class was nearly 3 times less affected than lower socioeconomic class. The infrequencies of dengue and chikungunya infections were observed to be 2 to 3 times higher in residents of Rangoon City than those of other towns. In Rangoon the antibody prevalence rates to dengue increased progressively with age while in other towns no appreciable increase in rates with age was observed. Both sexes were equally affected. This study provides strong circumstantial evidence that dengue and chikungunya viruses are highly and widely distributed throughout Burma, and that new outbreaks of haemorrhagic fever could occur in previously free areas following introduction of dengue viruses into populations previously exposed to one type of dengue.

An outbreak of plague in Hlegu, Burma in 1977.

An outbreak of plague occurred in Hlegu Town, Burma in February and March 1977. Altogether 14 bubonic plague cases, with 2 deaths were reported, mostly children under 15 years of age. Twice as many males as females were affected. A retrospective investigation showed that a rat fall took place in the last week of January. Only 9.5% of the rodents which died in the epizootic were found to be infected with Y. pestis; this apparent low infection rate probably resulted from the inclusion in the survey of some dead rats which died of other causes. 14.5% out of 48 trapped rodents were found to be serologically positive. The general flea and cheopis indices were rather high, perhaps because fleas were found to be partially resistant to DDT and also because spraying of insecticide did not effect fleas on the hosts. The cheopis index in Hlegu Town was 1.17, and less than 0.5 in Hlegu suburb (Yankin-Yat) where no epizootic was reported. An active case search revealed 76 suspected plague cases out of which 11 were found to have bubonic plague. A field trial showed that plague vaccination during the outbreak did not result in a rise of detectable antibodies in persons inoculated.

The effect of tetanus toxoid in leprosy patients.

Since cases of lepra reaction following smallpox vaccination and BCG vaccination had been reported the effect of tetanus immunisation on leprosy patients (whether it may provoke a lepra reaction or not) was studied. Three doses of purified tetanus toxoid (one ml initially, one ml after six weeks and one ml after six months) were given to 357 leprosy patients and 60 patients living in the same environ were followed as controls. The antibody response following immunisation was followed in six lepromatous leprosy patients using toxin antitoxin neutralisation test at the Lf/1000 level in mice and in three of them the antibody titre of leprosy patients rose to satisfactory level. The number of lepra reactions in these patients was monitored for nine months (two months before vaccination, during the six months period of vaccination and one month after the last dose of vaccine). There was no significant rise in the number of patients with reaction following the vaccination.

The unchanging epidemiology and toll of measles in Burma.

PIP: An evaluation of the public health importance of measles in Burma was carried out in 1983 to formulate recommendations regarding the feasibility of incorporating measles vaccine into the country's Expanded Program on Immunization (EPI). A review of available medical, serological, and epidemiological data as well as a sample study of childhood deaths indicated measles is a major killer of infants and young children in Burma. Since 1978, there have been over 20,000 cases of measles per year, and almost all children are infected with the measles virus by age 10 years. The clinical attack rate for measles is highest during the 2nd year of life. During the measles season, this virus accounts for 20% of all pediatric admissions and places an acute strain on the hospital system. Respiratory complications are noted in 50-90% of all measles admissions, while gastrointestinal complications range from 5-25%. The case-fatality rate of hospitalized measles cases averages 8.2%. Measles accounted for 87 (35%) of 280 childhood deaths occurring in selected townships in Rangoon in 1982-83, and less than 20% of these children had been hospitalized before death. Taking into account all available survey and study data, the overall case-fatality rate for measles in Burma can be conservatively estimated at 1-2%. Since about 1 million cases of measles occur each year, 10,000-20,000 measles deaths/year can be expected. It is concluded that measles' heavy toll in terms of child deaths will not change until measles' vaccine is routinely provided to all infants and young children. The use of measles vaccine on a wide scale is justified not only by morbidity and mortality considerations, but by the burden this disese places on hospital and outpatient resources.^ieng

Measurement of mortality from neonatal tetanus in Burma.

Surveys to determine mortality from neonatal tetanus were conducted in March and April 1985 in accessible areas of Burma, where pregnant women had been immunized with tetanus toxoid and, for comparison, also in areas where such immunization had not been given. Neonatal mortality rates were three times greater in areas where tetanus toxoid immunization had only recently or had not yet been introduced by the national expanded programme on immunization. Analysis of the data indicates that the impact on reduction of neonatal mortality from tetanus of three interventions (immunization of pregnant women with tetanus toxoid; delivery in hospital; or birth at home attended by a trained health worker) was greatest for immunization.

Clinical and laboratory studies on haemorrhagic fever in Burma, 1970-72.

This three-year serologic study of 2 060 children with a clinical diagnosis of haemorrhagic fever, who were admitted to the Children's Hospital and other hospitals in Rangoon, has shown that the etiology of the illness was multiple. Of all these patients, 347 (16.8%) had a dengue infection (96 with primary and 251 with secondary dengue infections), 510 (24.7%) had chikungunya infections, 55 (2.7%) had simultaneous chikungunya and dengue, 263 (12.8%) had influenza A infections, 62 (3.0%) had influenza B, 12 (0.6%) had measles, and there were 811 (39.4%) for whom no etiology could be established. Epidemiological and clinical features and laboratory findings are discussed. Evidence is presented for human infections with all four types of denguevirus in Rangoon.