Food of larval Anopheles culicifacies and Anopheles varuna in a stream habitat in Sri Lanka.

No previous studies have been conducted on the natural food of larval Anopheles culicifacies s.l. (the major malaria vector) and An. varuna (a secondary vector) in Sri Lanka. The present study analyzed the contents of guts dissected from larvae collected from pools in a natural stream-cum-irrigation conveyance channel in the Upper Yan Oya watershed in the North Central Province of the country during August-September 1997 and July 1998. Determinations of physicochemical and biological parameters of the pools and their water were done at the same time. A fluorochromatic stain, 4',6-diamidino-2-phenylindole, was used to stain larval gut contents. Quantitative estimates of different categories of food types were made by analyzing the gut contents of 95 An. culicifacies (26 second instars and 69 fourth instars) and 52 An. varuna (21 second instars and 31 fourth instars). Detritus was the most frequent food type, comprising >74% of the gut contents in both species. Other food types included bacteria (cocci and rods), filamentous algae, diatoms, and desmids. Overall, bacteria constituted a significantly higher proportion of the gut contents in An. culicifacies than in An varuna. Significantly more detritus, bacteria, and total particulate matter occurred in 4th instars of An. culicifacies than in An. varuna, indicating a greater food intake in the former species. Second instars of An. culicifacies and An. varuna did not differ significantly in any parameter. A significant increase in food intake between 2nd and 4th instars was seen for An. culicifacies, but not An. varuna. Food indices were lower in An. varuna than in An. culicifacies when the 2 species co-occurred, indicating competition for food, and the implications of this to adult body size, survival, and fecundity are discussed.

Physico-chemical characteristics of Anopheles culicifacies and Anopheles varuna breeding water in a dry zone stream in Sri Lanka.

BACKGROUND & OBJECTIVES: Selected physico-chemical characteristics of flowing and pooled water in a stream that generated two malaria vectors, Anopheles culicifacies s.l. Giles and Anopheles varuna Iyengar, were investigated during August-September 1997 and July 1998 at the Upper Yan Oya watershed in north-central Sri Lanka. METHODS: The physico-chemical parameters measured were: temperature, dissolved oxygen, pH, conductivity, total dissolved solids, alkalinity, ammonia nitrogen, nitrate nitrogen, calcium, magnesium, carbondioxide, ferrous iron, phosphate, colour and turbidity. In total, 75.5% of 151 samples analysed were mosquito-positive. Logistic regression was used for statistical analysis. RESULTS: Among physico-chemical parameters, An. culicifacies (the major malaria vector in the country) was positively related only to temperature, and An. varuna (a secondary malaria vector) to calcium. Among habitat characteristics, An. culicifacies was associated with light and vegetation, and negatively associated with the presence of potential predators. An. varuna was positively associated with other aquatic fauna. INTERPRETATION & CONCLUSION: Surprisingly this detailed study did not find an association between An. culicifacies and dissolved oxygen as previously found in the few studies that have looked at physico-chemical characteristics of malaria vector breeding habitats in south Asia. This study, along with existing information from other studies indicate that most of the physico-chemical parameters measured under natural conditions within the same habitat type is insufficient to explain the distribution of vectors within such habitats. However, it seems likely that both An. culicifacies and An. varuna follow a strategy whereby ovipositing females scatter their eggs over most of or all of a highly temporary and only transiently available stream bed pool habitat, in order to optimise breeding success.

Predicting Ixodes scapularis abundance on white-tailed deer using geographic information systems.

We collected 1,410 Ixodes scapularis from 139 white-tailed deer in Kent County, Maryland during the 1990 hunting season. A geographic information system was used to extract 41 environmental variables in the areas surrounding the collection sites of the deer. Stepwise linear regression was used to evaluate the association between the abundance of ticks on deer and the environmental data. A significant statistical association was observed between the abundance of I. scapularis and seven environmental variables (R = 0.69). Tick abundance was negatively correlated with urban land use patterns, wetlands, the amount of privately owned land, soils that tended to be saturated with water, and one drainage system. Tick abundance was positively correlated with well-drained, sandy soils having low water tables. These results indicate that geographically referenced environmental data may be useful in anticipating the risk of exposure to vectors over large areas.

Anopheline ecology and malaria infection during the irrigation development of an area of the Mahaweli Project, Sri Lanka.

A study on adult anopheline ecology and malaria vector incrimination was carried out from 1986 to 1989 during irrigation development in an area of the Mahaweli Project in eastern Sri Lanka. Eleven potential vector species were collected resting indoors or by using human or bovid bait, and from light trap catches. Overall, Anopheles vagus (Donitz), An. annularis (van der Wulp), and An. subpictus (Grassi) were the most prevalent, and An. culicifacies (Giles) and An. barbirostris (van der Wulp) were the least prevalent species. The abundance of An. aconitus (Donitz), An. jamesii (Theobald), An. pallidus (Theobald), and An. subpictus increased after irrigation development, while An. annularis, An. barbirostris, An. culicifacies and An. varuna (Iyengar) decreased. Populations of An. nigerrimus (Giles), An. tessellatus (Theobald), and An. vagus did not change substantially. Seven species were infected with malaria parasites, as determined by enzyme-linked immunosorbent assays (ELISA) done on mosquito head-thorax triturates. The main species involved were An. annularis, at peak abundance during the 1986-1987 period of development leading to the onset of irrigation, and An. subpictus, during times of seasonal abundance in the post-irrigation period of 1988 to 1989. Although occurring at low abundance, An. culicifacies was involved in malaria transmission irregularly throughout the study period. While there was strong ELISA-based evidence implicating An. subpictus as a major post-irrigation vector, confirmation of its vector status must await dissection and ELISA-based evidence of P. vivax and P. falciparum sporozoite infection rates in salivary glands.

Measuring the economic cost of malaria to households in Sri Lanka.

The economic cost at the household level of labor days lost due to malaria and other illnesses was estimated in a rural community in Sri Lanka. Over a one-year period, 223 episodes of malaria were recorded from the 298 inhabitants of the village. Based on daily activity records, the economically active age group was defined as 14-60 years. In this age group, 1.8% of working days were lost due to malaria and 5.2% due to all other illnesses. The value of a labor day lost was based on the actual rural wage rate for children, women, and men, with weeks during periods of high labor demand weighting more than weeks during lean agricultural periods. In this way the annual economic loss per household amounted to US $15.56 for malaria and US $47.46 for all other illnesses. This corresponded to a loss of 6% and 18% of annual household net income, respectively. Although the overall economic impact was limited, malaria cases were concentrated in an important agricultural season. During this season, 5.6% of working days were lost due to malaria. In addition, children, who were not part of the economically active population, lost 10% of school days due to malaria during the high transmission season. In estimating the socioeconomic impact of malaria and in measuring cost-benefits of malaria control interventions, these costs have to be considered together with direct expenditures incurred by households such as on treatment and travel and with costs for the service providers.

Malaria vectors in a traditional dry zone village in Sri Lanka.

Malaria transmission by anopheline mosquitoes was studied in a traditional tank-irrigation-based rice-producing village in the malaria-endemic low country dry zone of northcentral Sri Lanka during the period August 1994-February 1997. Adult mosquitoes were collected from human and bovid bait catches, bovid-baited trap huts, indoor catches, and pit traps. Mosquito head-thoraces were tested for the presence of Plasmodium falciparum and P. vivax, and blood-engorged abdomens for the presence of human blood by ELISAs. House surveys were done at two-day intervals to record cases of blood film-confirmed malaria among the villagers. A total of 7,823 female anophelines representing 14 species were collected. Trends in anopheline abundance were significantly correlated with rainfall of the preceding month in An. annularis, An. barbirostris, An. subpictus, An. vagus, and An. varuna, but were not significant in An. culicifacies and An. peditaeniatus. Malaria parasite infections were seen in seven mosquito species, with 75% of the positive mosquitoes containing P. falciparum and 25% P. vivax. Polymorph PV247 was recorded from a vector (i.e., An. varuna) for the first time in Sri Lanka. Computations of mean number of infective vector (MIV) rates using abundance, circumsporozoite (CS) protein rate, and human blood index (HBI) showed the highest rate in An. culicifacies. A malaria outbreak occurred from October 1994 to January 1995 in which 45.5% of village residents experienced at least a single disease episode. Thereafter, malaria incidence remained low. Anopheles culicifacies abundance lagged by one month correlated positively with monthly malaria incidence during the outbreak period, and although this species ranked fifth in terms of abundance, infection was associated with a high MIV rate due to a high CS protein rate and HBI. Abundance trends in other species did not correlate significantly with malaria. It was concluded that An. culicifacies was epidemiologically the most important vector in the study area.

Serologic evidence for an epizootic dengue virus infecting toque macaques (Macaca sinica) at Polonnaruwa, Sri Lanka.

Dengue is one of the most rapidly emerging diseases in the tropics. Humans are the principal reservoir of dengue viruses. It is unclear if nonhuman primates also serve as a reservoir of human dengue viruses under certain conditions. In this study, a cross-sectional serologic survey was carried out to characterize the pattern of transmission of a recently identified dengue virus among toque macaques in Sri Lanka. The results indicated that an epizootic dengue virus was active among the macaques. A single epizootic had taken place between October 1986 and February 1987 during which 94% of the macaques within the 3 km2 study site were exposed to the virus. The epizootic was highly focal in nature because macaques living 5 km from the study population were not exposed to the virus. The transmission of dengue viruses among macaques in the wild may have important public health implications.

Viruses isolated from mosquitoes collected in Sri Lanka.

Attempts to isolate viruses from 178,181 unengorged female mosquitoes collected from different ecologic areas of Sri Lanka yielded 31 isolates: 17 of Japanese encephalitis (JE) virus, nine of Getah virus, three of a Batai-related bunyavirus, and two of Arkonam virus. Culex tritaeniorhynchus and Mansonia uniformis mosquitoes were found to carry JE virus in a dry zone nonepidemic area, and Cx. pseudovishnui was found to carry it in a wet zone nonepidemic area. Japanese encephalitis virus was isolated from Cx. tritaeniorhynchus, Cx. gelidus, Cx. fuscocephala, and Cx. whitmorei during a human epidemic in the dry zone. Getah virus was isolated from Cx. tritaeniorhynchus, Cx. gelidus, and Cx. fuscocephala collected in the vicinity of swine. Isolations of Getah, Arkonam, and Batai-related viruses from Sri Lanka are reported for the first time.

Household responses to malaria and their costs: a study from rural Sri Lanka.

A study of the cost of malaria at the household level, community perceptions, preventive measures and illness behaviour linked to the disease was undertaken in 5 villages in the dry zone of Sri Lanka. The surveyed community had a high knowledge of malaria, although side effects of antimalarial drugs were often confused with symptoms of the disease. The community sought prompt diagnosis and treatment at 'western-type' facilities, with 84% making use of government facilities as their first choice and 16% preferring private facilities. The preventive measures used were burning coils (54% of families) and special leaves (69% of families), and 93% of the families had their houses sprayed with insecticides. Average direct expenditure on a single malaria episode was $3 US, with some families spending more than 10% of the annual household net income per episode. The highest expenditure was on special diets for the sick person, to neutralize the perceived heating effect of the disease and its treatment.

PIP: Knowledge of community perceptions of malaria, treatment-seeking behaviors, and the household costs of illness is essential to the planning of sustainable malaria control interventions. These factors were investigated in household surveys conducted in 5 villages in Sri Lanka's dry zone in February 1995. 95% of the 216 families interviewed regarded malaria as their main health problem, followed by diarrhea and eye diseases. Malaria was ranked as the third most important community concern, following lack of water for cultivation and poverty. Overall knowledge of malaria's causes, symptoms, and treatment was high, although the side effects of antimalarial drugs were often confused with symptoms of the disease. Reported for the 3-month period preceding the survey were 178 episodes of malaria involving 160 families. Home treatment with paracetamol was the first step taken in 85% of cases; however, all families sought prompt treatment from Western-type facilities, especially government hospitals (48%) and mobile clinics (30%). No families consulted indigenous or ayurvedic physicians, despite their availability in the area. This utilization of prompt, effective treatment is presumed to reflect high knowledge about malaria, the perceived seriousness of the disease, and good transport facilities in the area. The total direct expenditure on a single episode of malaria averaged US $3; the median net annual income was $258. Special foods for malaria patients aimed at neutralizing the perceived heating effect of malaria and antimalarial drugs (e.g., sodas, oranges) were the most costly item. Adults lost an average of 7.8 days of work per episode and those accompanying them to health facilities lost 2.9 days. Preventive measures used by families included bed nets (23%), mosquito coils (54%), and insecticides (93%).

Risk factors for malaria: a microepidemiological study in a village in Sri Lanka.

Environmental and socioeconomic risk factors for malaria were studied in a village in Sri Lanka. Over a period of one year, all 49 households in the village were visited every alternate day to obtain information on malaria episodes. Information on risk factors was obtained through questionnaires and direct observations. Age below 17 years (relative risk [RR] = 1.66, 95% confidence interval [95% CI] 1.18-2.35), use of bed nets (RR = 0.16, 95% CI 0.05-0.45) and traditional fumigants (RR = 0.58, 95% CI 0.37-0.93) were independent predictors of malaria. People using anti-mosquito pyrethrum coils had a higher risk for malaria than people living in houses where they were not used (RR = 1.46, 95% CI 1.03-2.07). The build-up of Anopheles culicifacies populations before the start of the transmission season had taken place in a stream near the village. Living close to the stream was a risk factor for malaria early in the transmission season, although this did not reach statistical significance (comparing < 250 m with > 500 m, RR = 2.13, 95% CI 0.96-4.71).

Japanese encephalitis in Sri Lanka--the study of an epidemic: vector incrimination, porcine infection and human disease.

A prospective study of mosquito vectors, porcine infection and human disease was carried out during a Japanese encephalitis (JE) epidemic in the North Central province of Sri Lanka (November-December 1987) and a subsequent non-epidemic year (1988). The epidemic involved 361 cases of human encephalitis, virologically confirmed by immunoglobulin M enzyme-linked immunosorbent assay (ELISA), and was preceded 2-3 weeks earlier by sentinel porcine seroconversion. Virus isolation and viral antigen detection (ELISA) in field-caught mosquitoes incriminated Culex tritaeniorhynchus (Giles) and Cx gelidus Theobald as the major vectors of virus transmission during the porcine amplification and human 'spill-over' phases of the epidemic. Virus was also demonstrated in Cx fuscocephala Theobald, Cx whitmorei (Giles) and Mansonia uniformis (Theobald) during the epidemic. The major difference between the epidemic (1987) and non-epidemic (1988) years was a lower vector biomass and lower rates of virus carriage in the mosquito population.

Japanese encephalitis in Sri Lanka: comparison of vector and virus ecology in different agro-climatic areas.

The ecology of Japanese encephalitis (JE) in different agro-climatological areas of Sri Lanka was studied in relation to the abundance of mosquito vectors, infection in domestic livestock, and human infection and disease. There was an inverse correlation between altitude and the abundance of potential JE vectors, as well as JE seroprevalence in domestic livestock and in man. Little or no JE infection was documented above 1200 m elevation. JE seroprevalences in cattle and goats were better predictors of human infection risk than was porcine seroprevalence. In areas with asynchronous porcine infection occurring over many months, high overall JE seroprevalence in pigs was found with little evidence of human infection. Porcine JE infection occurring in synchronous bursts associated with monsoonalrains was correlated with significant bovine, ovine and human seroprevalence in 2 low elevation study areas, Anuradhapura (dry zone) and Ragama (wet zone), with epidemic human JE in the former area and endemic disease in the latter.

Human otoacariasis: a retrospective study from an area of Sri Lanka.

Intra-aural ticks were present in 870 (15.2%) of 5714 patients who reported with ear-related complaints to the ear, nose and throat ward at Ratnapura Hospital, Sabaragamuwa Province, Sri Lanka, from January 2000 to December 2001. A retrospective study of 383 of these otoacariasis cases showed that the majority (70.8%) of surgically-removed ticks were nymphal Amblyomma integrum, together with nymphal and adult Rhipicephalus haemaphysaloides, R. sanguineus, Hyalomma brevipunctata, H. marginatum, and unidentified (damaged) ticks (collectively, 29.2%). Tick infestations peaked during the period November-February. More female than male patients reported with otoacariasis, and more children (aged 0-10 years) and adults (aged >/=21 years) than adolescents. There was no evidence of age-dependent differences in infestation among male and female patients. The tick-infested cases were widespread, spanning 75 km on a north-south axis and 55 km on an east-west axis within Sabaragamuwa Province. The present report represents the largest episode of human otoacariasis recorded in the literature, and may be indicative of a wider, but little-reported, human tick problem in Sri Lanka.

Anopheles culicifacies breeding in Sri Lanka and options for control through water management.

This paper assesses the options for control of malaria vectors through different water management practices in a natural stream in Sri Lanka. The association between water level in the stream and breeding of the immature stages of the primary vector Anopheles culicifacies was investigated and the feasibility of using existing irrigation infrastructure to reduce the breeding potential discussed. The most feasible option would be to implement a management routine where water is released periodically from an upstream reservoir to reduce the number of breeding sites downstream. This study indicates that by regulating the water level above 20 cm in the stream throughout the dry season the breeding of A. culicifacies could be significantly reduced. The intervention would have only limited impact on the water lost for agriculture and the management input would be minimal. However, for the intervention to work a high degree of support from the local community is essential and consultation between government departments needed.

A village treatment center for malaria: community response in Sri Lanka.

Early diagnosis and treatment of malaria cases is one of the basic elements of the current global malaria control strategy. In order to provide this service to people in rural areas there is a need for new cost-effective approaches. To ensure that such new approaches are acceptable to the target communities, it is important to know the rationale for people's malaria treatment-seeking behavior. The present study provides insights into the reasons for people's preferences for different types of healthcare facilities and describes variation of these preferences within a rural community in Sri Lanka. The study reports on the experiences with the establishment of a village health facility and its effect on the treatment-seeking behavior of the population. After the introduction of the village treatment center it quickly took over the role of main provider for diagnosis and treatment of malaria from the government facilities. The treatment center did not improve the response time in seeking treatment for young children, but the delay for adults was reduced by 1-2 days. Mothers with small children often preferred the government facilities since they wanted a more qualified opinion than available from the locally recruited staff of the village treatment center. The treatment center significantly reduced the stress and discomfort experienced by the elderly and handicapped segment of the community. The study indicated that the effective catchment area of a village treatment center will be influenced by the degree of initial support from key individuals in the communities, the selection procedure and training of assistants, and the history of the relationships between different villages to be served by the center. The government health services and communities across the dry zone of Sri Lanka could benefit substantially from the establishment of more village treatment centers. To ensure the long-term sustainability of these type of facilities it is necessary to assess the feasibility of charging a user fee and establishing multi-purpose clinics. Government policies and administrative procedures will need to be adjusted to make the successful operation of village treatment centers possible.

Postirrigation breeding patterns of surface water mosquitoes in the Mahaweli Project, Sri Lanka, and comparisons with preceding developmental phases.

A 2-yr (1988-1989) survey of mosquitoes breeding in surface water was done in an area of the Mahaweli Project of Sri Lanka that underwent irrigation development and human settlement during the preceding 3 yr. In total, 78,649 immatures of 42 species were collected during the survey. Species of medical importance in the area were Anopheles annularis van der Wulp, An. culicifacies Giles, An. jamesii Theobald, An. nigerrimus Giles, An. subpictus Grassi, An. vagus Doenitz, An. varuna Iyengar, Mansonia annulifera (Theobald), Ma. uniformis (Theobald), Culex fuscocephala Theobald, Cx. gelidus Theobald, Cx. pseudovishnui Colless, Cx. tritaeniorhynchus Giles, and Cx. vishnui Theobald. These and other species used breeding habitats associated with irrigation development (i.e., canals, reservoirs, seepage pools, and rice fields) as well as natural habitats (i.e., rainwater pools, riverbed pools, streams, and marshes). Trends in the use of breeding habitats that were observed with the onset of irrigated rice cultivation in 1987, continued during the period under stable irrigation in 1988 and 1989. Mosquito species richness declined, but species equitability (as indexed by Shannon-Weaver diversity values) did not change. The overall study showed that ecosystem changes concomitant with irrigation development in the Mahaweli Project resulted in long-term changes in the composition of the mosquito fauna, which was characterized by the increasing dominance of species with the potential to transmit human pathogens.

Survey of adult mosquitoes (Diptera: Culicidae) during irrigation development in the Mahaweli Project, Sri Lanka.

A survey of adult mosquitoes was done during 1986-1987 in an area undergoing irrigation development in the Mahaweli Project of Sri Lanka. The study encompassed two 12-mo phases of settlement and irrigation, respectively. Diurnal human bait catches yielded 1,427 female mosquitoes in 27 species. Nocturnal collections (human bait, CDC light traps, indoor resting catches) produced a total of 30,491 females in 67 species. Comparisons with an earlier survey in the predevelopment forest showed that the diurnal human biting abundance of Aedes albopictus (Skuse) remained stable, whereas the abundance of Ae. novalbopictus Barraud and Ae. w-albus Theobald declined drastically after development. Man-mosquito contact increased substantially for nocturnally active Anopheles annularis van der Wulp, An. subpictus Grassi, Mansonia uniformis (Theobald), Culex tritaeniorhynchus Giles, and Cx. quinefasciatus Say and decreased for Ma. annulifera (Theobald) and Cx. gelidus Theobald. A small increase occurred in An. culicifacies Giles, An. vagus Donitz, An. varuna lyengar, Cx. fuscocephala Theobald, and Cx. whitmorei (Giles); Cx. pseudovishnui Colless decreased. The effect of changes in mosquito abundance on the increased transmission of malaria and Japanese encephalitis is discussed.

Larval survey of surface water-breeding mosquitoes during irrigation development in the Mahaweli Project, Sri Lanka.

A survey of ground water-breeding mosquitoes was done during 1986-1987 in an area undergoing irrigation development in the Mahaweli Project of Sri Lanka. Forty-nine species were collected during the 12-mo phase of humans settlement and infrastructure construction, and 42 species during the succeeding 12-mo period under irrigated rice culture. Development resulted in the elimination of some preexisting breeding habitats, the modification of others, and the creation of new habits. The overall change from uninhabited forest to settled irrigated rice sharply increased the prevalence of Anopheles annularis van der Wulp, An. peditaeniatus (Leicester), Aedeomyia catasticta Knab, Mimomyia hybrida (Leicester), Mansonia uniformis (Theobald), and Culex tritaeniorhynchus Giles. Equally sharp decreases occurred in the prevalence of An. barbirostris van der Wulp, An. barbumbrosus Strickland & Choudhury, Ae, jamesi (Edwards), Ae. vittatus (Bigot), Ae. pseudomediofasciatus (Theobald), Cx. halifaxii Theobald, Cx. malayi (Leicester), Cx. minutissimus (Theobald), Cx. nigropunctatus Edwards, Cx. fuscocephala Theobald, and Cx. mimulus Edwards. Other species that showed smaller positive or negative changes included An. nigerrimus Giles, An. culicifacies Giles, An. jamesii Theobald, An. subpictus Grassi, An. vagus Donitz, An. varuna Iyengar, Mi. chamberlaini (Ludlow), Ma. annulifera (Theobald), Cx. bitaeniorhynchus Giles, Cx. gelidus Theobald, and Cx. pseudovishnui Colless. Irrigation development led to reduced breeding by the majority of species; however, most species that did increase in prevalence were potential vectors of human disease. Components of the irrigation system such as reservoir and canal margins, seepages, and rice fields provided increased breeding sites for some of these species.

Anopheline (Diptera:Culicidae) breeding in a traditional tank-based village ecosystem in north central Sri Lanka.

A 13-mo survey of immature anopheline mosquitoes breeding in surface water habitats was done at Mahameegaswewa village within the Huruluwewa watershed in north central Sri Lanka as part of a multidisciplinary study on malaria epidemiology. The watershed is representative of the ancient small tank-based irrigation network that still forms an important component of the rice production system in the low elevation dry zone. In total, 3,818 immatures representing 12 species were obtained from 2,940 samples taken from 5 larval habitats within the village ecosystem. Anopheles varuna Iyengar and An. culicifacies Giles were the most abundant species collected. Peak abundance in both species occurred in August-October. Anopheles barbirostris Van der Wulp and An. peditaeniatus Leicester also were abundant, but neither these nor the other anophelines attained comparable abundance to An. varuna and An. culicifacies. A clear progression in breeding habitat use from stream bed to tank bed and drainage area pools was seen in An. culicifacies during the premonsoon period. Environmental management measures to reduce or modify these habitats could potentially decrease malaria. transmission.

Increasing density and Borrelia burgdorferi infection of deer-infesting Ixodes dammini (Acari: Ixodidae) in Maryland.

A statewide survey of Ixodes dammini Spielman was done in November 1991 as a follow-up to a study in 1989. In total, 3,434 adult ticks were collected from 922 hunter-killed white-tailed deer processed at 22 check stations (1 per county in 22 of 23 counties in the state). Significantly more male than female ticks were collected. Tick infestation was significantly heavier on male than female deer. The pattern of tick distribution was similar to that in 1989, with low prevalence (percentage tick-infested deer) and abundance (mean ticks per deer) in the Appalachian region, moderate values in the Piedmont, and high values in the western and eastern Coastal Plains regions. The pattern of tick infection with Borrelia burgdorferi spirochetes (determined by polyclonal immunofluorescence assay) was similar to the tick distributional pattern. Overall, tick prevalence and abundance were higher in 1991 than in 1989, as was the spirochete infection rate in ticks. Multiple regression analysis of tick prevalence against six selected physical and biotic parameters (elevation, rainfall, summer and winter temperature, percentage of forest land, deer density) showed a significant relationship with rainfall and elevation in 1989 and elevation alone in 1991. A more extensive study in Caroline and Dorchester counties in the eastern Coastal Plains region (which showed exceptionally low tick density indices in a generally tick-abundant region in 1989) demonstrated that I. dammini was well established in Caroline but not in Dorchester County.