The fauna and the geographical distribution of vectors of Chagas' disease were investigated based on the man-hour collection, from mud walls or palm-thatched houses in 236 villages, from the year 1995 through 1997, throughout Guaternala. A total of 1,131 vectors cornprising 731 (64,6%) of Triatoma dimidiata, 53 (4,7%) of Tl nitida and 347 (30,7%) ofRhodniusProlixus were found. 71 dimidiata was collected in 16 eut of 22 departments, whereas R. Prolixus was collected in five departments, and T nitida was collected only in three departments. The total number of R, prolixus was not small, 85% of the bugs was collected frorn 800 m to 1,400 m above sea level in the present study areas. We collected more bugs in the east and the southeast departrnents of the country, such as in the borders with Honduras and El Salvador. The rate of positive houses with bugs is the highest in Jutiapa, followed by Alta Verapaz, Chiquimula, Santa Rosa, and Quiche. The bug density in the investigated houses is the highest in Chiquimula, while the geographical dispersion of bugs is the widest in Jutiapa. The natural infection of bugs with Trypanosoma cntzi is the highest in Zacapa. Based on the above-rnentioned positive rate of bugs and from the data of the 1994 National Census in Guatemala, we concluded

T. dimidiata is widely distributed in the country, and is also the main vector in at least ten departments, but R. prolixus with higher vectorial capacity is an important vector in at least two departments. Key words: Trypanosoma infection rate -Triatoma dimidiata -Triatoma nitida -Rhodnius prolixus -vectors' sex ratioGuatemalaTrypanosoma cruzi and Trypanosomana rangeli are parasitic protozoans of insect vectors of the Triatominae subfamily and vertebrates, specifically mammals. T. cruzi is the causative agent of Chagas disease, while T. rangeli is non pathogenic to humans and other vertebrate hosts. In the vector, T. cruzi develops in the intestinal tract, while T. rangeli has the ability to invade and develop in the hemolymph and salivary glands (Grisard et al. 1999). In Guatemala, the first reports of the presence of T. cruzi and T. rangeli in humans were in 1932 and 1934, respectively (Reichnow 1933, Blanco 1943, De León 1949.Reports of T. cruzi and T. rangeli infection in triatomine vectors of Central America, suggest that rates of infection differ among species and regions. For example, in Panama, Sousa and Johnson (1973) Reports of the infection rates of T. rangeli in the vectors from South America also give some idea of differences between regions. Marinkelle (1968), in Colombia, reported five out of 29 T. dimidiata capitata infected with T. rangeli in the salivary glands.In addition to variable rates of parasite infection among vectors, different rates of human infection are related with different vector species or populations, suggesting that vectors may differ in their ability to transmit T. cruzi. For example, in Guatemala, T. dimidiata appears to be associated with lower levels of human seroprevalence compared to R. prolixus. In one village of the department of Zacapa where R. prolixus was the principal vector, the seroprevalence amongst 373 people tested was 38.8%. In another village in the department of Santa Rosa, where the only vector found was T. dimidiata, a much lower seroprevelance rate was found: 8.9% of the 428 people tested were seropositive for T. cruzi (Paz-Bailey et al. 2002). This trend was also noted in Honduras in a region where 35% of houses were infested with R. prolixus, seroprevalence in the population was 40%, while in another area, where only T. dimidiata was present, the prevalence of human infection was only 15% (Ponce et al. 1995). These results suggest that R. prolixus is a more efficient vector than T. dimidiata.

The number of Triatoma dimidiata found per rnan-hour of collection in each of the three mud-walled houses were 4, 1 and 37, In the third house 8 of T nitida were also collected.When the walls of these houses were dismantled, an additional 1 14, !41 and 307 of Tl dimidiata were cellected along with 34 of T nitida in the third house, In the palm-thatch roofed huts only Rhodnius Protixus were collected. The numbers per man-hour collected were 1 1, 27 and 26. When the roofs were dismantled and searched 75, 449 and 978 bugs were found in the respective houses. These results indicate that the numbers collected by the traditional method did not accurately refiect the population density in the houses, The collections indicate that the hiding places of 71 dimidiata and R, Prolixus were very lirnited within the houses, An average of 31% of T dimidinta were collected in only two dismantled block sections (2m2) which were close to the beds and chicken nest and 40% of R. protixus in the last house were obtained in the lower section of the palm-thatched roofs just abeve a bed, This area occupied only 4.2% area in total space of the house, These results suggest that insecticidal treatments would be most effective if they focused on the places where more bugs concentrate.

Abstract. To examine the existence of a possible threshold for the domestic infestation rate of Triatoma dimidiata, below which transmission becomes unlikely, a census was conducted in 59 Chagas disease endemic communities of El Salvador and Honduras. Entomological and serological tests were conducted targeting 4,083 households and 6,324 children between 6 months and 15 years of age. The overall domestic infestation rate of Triatoma dimidiata and seroprevalence among children were 12.9% and 0.49%, respectively. Communities with a domestic infestation rate at 8% or less consistently showed a seroprevalence of 0%. In communities with a domestic infestation rate above 8%, there was a wide range in seroprevalence. A domestic infestation rate of 8% could serve as the possible threshold below which transmission would become unlikely. The implementation of an 8% threshold for determining needs for universal insecticide spraying would lead to a 21% reduction in spraying-related costs.

Abstract. Chagas disease is one of the most serious health problems in Latin America. Because the disease is transmitted mainly by triatomine vectors, a three-phase vector control strategy was used to reduce its vector-borne transmission. In Nicaragua, we implemented an indoor insecticide spraying program in five northern departments to reduce house infestation by Triatoma dimidiata. The spraying program was performed in two rounds. After each round, we conducted entomological evaluation to compare the vector infestation level before and after spraying. A total of 66,200 and 44,683 houses were sprayed in the first and second spraying rounds, respectively. The entomological evaluation showed that the proportion of houses infested by T. dimidiata was reduced from 17.0% to 3.0% after the first spraying, which was statistically significant (P < 0.0001). However, the second spraying round did not demonstrate clear effectiveness. Space-time analysis revealed that reinfestation of T. dimidiata is more likely to occur in clusters where the pre-spray infestation level is high. Here we discuss how large-scale insecticide spraying is neither effective nor affordable when T. dimidiata is widely distributed at low infestation levels. Further challenges involve research on T. dimidiata reinfestation, diversification of vector control strategies, and implementation of sustainable vector surveillance.