Risk of malaria in visitors to the Kruger National Park, South Africa

Host preference patterns in domestic and wild settings: Insights into Anopheles feeding behavior

The adaptation of Anopheles malaria vectors to domestic settings is directly linked to their ability to feed on humans. The strength of this species-habitat association is unequal across the species within the genus, with the major vectors being particularly dependent on humans. However, our understanding of how blood-feeding behavior interacts with and adapts to environmental settings, including the presence of humans, remains limited. Using a field-based approach, we first investigated Anopheles community structure and feeding behavior patterns in domestic and sylvatic settings in La Lopé National Park in Gabon, Central Africa. We characterized the preference indices using a dual-host choice sampling approach across mosquito species, habitats, and seasons. We then quantified the plastic biting behavior of mosquito species in each habitat. We collected individuals from 16 Anopheles species that exhibited significant differences in species composition and abundance between sylvatic and domestic settings. The host-seeking behavior also varied among the seven most abundant species. The general attractiveness to each host, human or animal, remained relatively constant for each species, but with significant variations between habitats across species. These variations, to more generalist and to more anthropophilic behavior, were related to seasonal changes and distance from the village, respectively. Finally, we pointed out that the host choice of major malaria vectors changed in the absence of humans, revealing a plastic feeding behavior of these species. This study highlights the effect of humans on Anopheles distribution and feeding evolution. The characterization of feeding behavior in wild and domestic settings provides opportunities to better understand the interplay between genetic determinants of host preference and ecological factors. Our findings suggest that protected areas may offer alternative thriving conditions to major malaria vectors.

Risk of malaria among French adult travellers

BACKGROUND

Imported malaria remains an important, but often unrecognised, health problem in Europe. Little information exists on the incidence of imported malaria with respect to exposure. This study aimed to estimate the incidence of malaria in a cohort of travellers with respect to protection measures.

METHOD

In all 13,017 participants enrolled in a French general population cohort (SU.VI.MAX cohort) and followed-up over 8 years were investigated. All participants received a retrospective questionnaire about travel to malaria-endemic countries relating to countries visited, duration of stay, use of protection measures and chemoprophylaxis. Malaria cases was confirmed from medical records.

RESULTS

Data were obtained for 752 individuals who made 1,393 trips to malaria-endemic areas. This sample was predominantly middle-class and high-risk groups such as migrants were not represented. Mechanical protection was used in 589 trips (42.3%) and chemoprophylaxis in 1,017 trips (73.0%). This was appropriate for the zone in 615 trips (44.0%) and adequate compliance was reported in the case of 497 trips (35.6%). Appropriate chemoprophylaxis and physical protection measures were used in 21.7% of the trips. Six laboratory-confirmed cases of imported malaria yielded an estimated incidence density of 148 cases/month of exposure/10,000 travellers. In five cases, appropriate protection measures had not been taken.

CONCLUSION

Appropriate chemoprophylaxis and physical protection measures against malaria infection are used by less than one-quarter of a sample of predominantly middle-class travellers from France to endemic areas. More intense education measures need to be implemented to reduce the risk of imported malaria.

Repellent effects on Anopheles arabiensis biting humans in Kruger Park, South Africa

Distribution of biting sites on the human body by the malaria vector Anopheles arabiensis Patton (Diptera: Culicidae) was investigated near a source of mosquitoes in the Kruger National Park, South Africa. Eight adult male volunteers (2 teams x 2 pairs of subjects) conducted human bait collections while seated on camp chairs in the open-air, wearing only short trousers (no shirt, socks or shoes). Mosquito collections during 18.30-22.30 hours on five consecutive nights in April 1998 yielded a total of 679 An. arabiensis females biting subjects with or without their ankles and feet treated with deet insect repellent (15% diethyl-3-methylbenzamide, Tabard lotion). On subjects whose feet and ankles were smeared with repellent, 160 An. arabiensis females were captured biting in 60 manhours: 88.1% on the legs, 1.4% on the arms and 1.2% on other parts of the body, but none on the repellent-treated feet or ankles. On subjects without repellent treatment, 519 An. arabiensis were caught biting in 60 man-hours: 81.1% on feet and ankles, 16.4% on legs, 1.4% on arms and 1.2% on the rest of the body. For individual subjects, the reduction of An. arabiensis bites ranged from 36.4 to 78.2% (mean protection 69.2%). Results of this study confirm previous findings that, in this part of South Africa - inhabited only by wildlife - when people sit outside during the evening An. arabiensis prefers to bite their lower limbs: 97.5% below the knees. Overall, the number of bites by the malaria vector An. arabiensis was reduced more than three-fold (from 26 to 8/person/evening), simply by treating ankles and feet with a consumer brand of deet repellent. Whether or not this provides a satisfactory degree of protection against malaria risk would depend on the malaria sporozoite rate in the malaria vector population.

Efficacy of three insect repellents against the malaria vector Anopheles arabiensis

Three commercial repellents marketed in South Africa: Bio-Skincare (BSC, oils of coconut, jojoba, rapeseed and vitamin E), Mosiguard towelletes with 0.574 g quwenling (p-menthane-3,8-diol, PMD) and the standard deet (15% diethyl-3-methylbenzamide, Tabard lotion), were compared against a laboratory colony of the mosquito Anopheles arabiensis Patton (Diptera: Culicidae), the predominant malaria vector in South Africa. Human forearms were treated with 1.2 g BSC, 0.8 g PMD towelette or 0.5 g deet and exposed to 200 hungry An. arabiensis females for 1 min, at intervals of 1-6 h post-treatment. Tests were conducted by three adult male volunteers (aged 30-45 years, crossover controlled test design for 3 consecutive days), using their left arm for treatment and right arm for untreated control. Biting rates averaged 39-52 bites/min on untreated arms. All three repellents provided complete protection against An. arabiensis for up to 3-4 h post-application; deet and PMD gave 90-100% protection up to 5-6h, but BSC declined to only 52% protection 6h post-treatment. These results are interpreted to show that all three repellent products give satisfactory levels of personal protection against An. arabiensis for 4-5 h, justifying further evaluation in the field.

Use of medical chemoprophylaxis and antimosquito precautions in Danish malaria patients and their traveling companions

BACKGROUND

The number of malaria cases imported to Denmark has been increasing for some years. To analyze the background for this we assessed the use of protective measures in Danish travelers visiting malarious areas.

METHOD

Post-travel questionnaires were given during hospitalization to malaria patients, and sent by mail to their traveling companions.

RESULTS

In total, 142 persons participated. Only 32% of the travelers used chemoprophylaxis correctly, according to Danish recommendations. Twelve percent of the travelers did not use chemoprophylaxis. Average compliance was 52%. Insufficient drug dosage was reported by 13%, and use of nonrecommended drugs by 7% of the travelers. Thirty-seven percent used insufficient antimosquito precautions, a problem which often coincided with irregular use of chemoprophylaxis. Malaria patients, sole travelers, and travelers with other ethnical background than Danish, were subgroups using insufficient malaria prophylaxis more frequently than healthy traveling companions.

CONCLUSION

Insufficient use of the available antimalaria precautions by Danish travelers contributes greatly to maintaining a high incidence of imported malaria. Increased attention from physicians in educating travelers is important for optimizing malaria prophylaxis.

Risk to tourists posed by wild mammals in South Africa

BACKGROUND

One of South Africa's principal tourist attractions is the opportunity to encounter Africa's large mammals in the wild. Attacks by these mammals can be exceptionally newsworthy with potentially deleterious effects on tourism. Little is known about the risk of injury and death caused by wild mammals to visitors to South Africa's nature reserves. The aim of this study was to determine the incidence of fatal and nonfatal attacks on tourists by wild mammals in South Africa and to ascertain avoidable factors, if any.

METHODS

Commercial press records covering all South African Newspapers archived at the Independent Newspapers' central library were systematically reviewed for a 10-year period, January 1988 to December 1997 inclusive, to identify all deaths and injuries to domestic and international tourists resulting from encounters with wild mammals in South Africa. All of these incidents were analyzed to ascertain avoidable factors.

RESULTS

During the review period seven tourists, including two students from Thailand and a German traveler, were killed by wild mammals in South Africa. Three of the four deaths ascribed to lions resulted from tourists carelessly approaching prides on foot in lion reserves. A judicial inquiry found that the management of a KwaZulu-Natal Reserve was culpable for the remaining death. Tourist ignorance of animal behavior and flagrant disregard of rules contributed to the two fatalities involving hippopotami. The unusual behavior manifested by the bull elephant responsible for the final death, resulted from discomfort caused by a dental problem to this pachyderm. During the same period there were 14 nonfatal attacks on tourists, including five by hippo, three by buffalo, two by rhino, and one each by a lion, leopard, zebra and musth elephant. Only the latter occurred while the visitor was in a motor vehicle. Tourist ethological naivete and failure to determine the experience of trail guides prior to travel, resulted in inadvertent agonistic behavior, unnecessary risk-taking and avoidable injury.

CONCLUSIONS

This retrospective study has shown that attacks on tourists by wild mammals in South Africa are an uncommon cause of injury and death. Sensible precautions to minimize this risk include remaining in a secure motor vehicle or adequately fenced precincts while in the vicinity of large mammals, rigidly observing nature reserve instructions, never approaching animals that appear ill, malnourished, displaying aggressive behavior traits or female wild mammals with young, and demanding adequately trained and experienced game rangers when embarking on walking trails. Any behavior that might be construed as antagonistic and which could provoke an attack by large mammals should be avoided (e.g., driving directly at a lion). Visitors need to be informed of classic signs of aggression, in particular in elephants, which will allow timely avoidance measures to be taken. The risk-enhancing effect of excessive alcohol intake is undesirable in the game reserve setting, as is driving at high speed after dusk in areas where hippos graze. Local advice on personal safety in wildlife reserves and the credentials of trail guides should be obtained from lodge or reserve management, tourism authorities or the travel industry prior to travel to game reserves.

Health risks of travelers in South Africa

Large numbers of tourists visit South Africa every year. Travelers to urban areas are at little risk of contracting an infectious disease, however the adventure traveler is at increased risk. Yellow fever is not known to occur in South Africa. Malaria is endemic in Mpumalanga and KwaZula-Natal. Schistosomiasis is endemic in large parts of the country. Although rabies is found throughout the country, only a small number of human cases is reported. High risk areas are KwaZulu-Natal, the eastern Cape and Mpumalanga provinces. The incidence of human immunodeficiency virus (HIV) infection is high and counseling regarding sexually transmitted diseases is important. Sanitation of water is excellent in most large cities and towns; however travelers to rural areas should exercise caution. Arbovirus infections do occur but relatively few cases are reported. The hiker is at risk for tick bite fever and should be counseled. Since the abolition of apartheid, South Africa has been seen as an inexpensive, high quality destination by many tourists. In 1997, a total of 5,436,848 travelers from many different countries visited the country. Areas most frequently visited include Johannesburg, Cape Town, Durban, the Garden Route, Kruger National Park, KwaZulu-Natal and Pretoria. The most common reason for visiting the country was holiday (44%), followed by visiting friends and relatives (23%), business travel (27%) other (6%).1 Travelers, to the larger cities such as Johannesburg, Cape Town and Durban are at little risk of acquiring an infectious disease. The adventure traveler however is at greater risk as parts of the country are endemic for malaria, schistosomiasis, rabies, food and waterborne diseases, sexually transmitted diseases and arbovirus infections. Accidental deaths due to motor vehicle accidents and interpersonal violence are important health risks in South Africa. Travelers visiting popular attractions are at significantly lower risk. However this has never been quantified. This review aims to address the occurrence of infectious diseases and attempts to give guidelines to practitioners caring for travelers.