**8. Possible alternatives to DDT**

Several vector control methods are currently available as alternatives to DDT, while others are under development. As previously stated, the use of alternative insecticides in IRS and the use of insecticide-treated bed nets (ITNs), are mainstreamed because of their proven im‐ pact on the malaria burden. Moreover, several non-chemical approaches could play a pivo‐ tal role in the future. Table 1 summarizes some possible alternative methods to DDT.



**Table 1.** Alternative methods for malaria vector control. Adapted from (van den Berg, 2009)

#### **8.1. Chemical methods**

and often with high levels of immune impairment, have been found in studies in South Afri‐ ca and Mexico (Aneck-Hahn et al., 2007; Bouwman et al., 1991; De Jager et al., 2006; Yanez et al., 2002), but contemporary peer-reviewed data from India, the largest consumer of DDT, are lacking. The simultaneous presence of, and possible interaction between, DDT, DDE and PYs in human tissue is another area of concern (Bouwman et al., 2006; Longnecker, 2005). In North America, rather high levels of exposure have been recorded in biological samples col‐ lected in the 1960s (Eskenazi et al., 2009). DDT accumulates in fatty tissue and is slowly re‐ leased. The half-life of DDT in humans is > 4 years; the half-life for DDE is probably longer

Several vector control methods are currently available as alternatives to DDT, while others are under development. As previously stated, the use of alternative insecticides in IRS and the use of insecticide-treated bed nets (ITNs), are mainstreamed because of their proven im‐ pact on the malaria burden. Moreover, several non-chemical approaches could play a pivo‐

attractants yes adult under development local, private sector resistance, toxicity

breeding sites no larva available local negligible fungi no adult under development not applicable negligible

methods no adult under development not applicable to be studied

manipulation no larva available local, agricolture sector negligible

improvement no adult available local, development programs resistance

**stage Availability Delivery/Resources Risk**

no larva available irrigation sector negligible

available local toxicity

resistance, effect on ecosystems

tal role in the future. Table 1 summarizes some possible alternative methods to DDT.

(Longnecker, 2005).

**Alternatives to DDT**

chemical

design of irrigation structures

elimination of

genetic

habitat

house

**8. Possible alternatives to DDT**

348 Insecticides - Development of Safer and More Effective Technologies

**Chemical (yes/no)**

botanicals no larva

**Vector**

adult

larviciding yes larva available spray teams

The strength of IRS with insecticides lies in its effect on shortening the life span of adult mosquitoes near their human targets (MacDonald, 1957). Two new approaches are currently being developed with regard to IRS, including some existing insecticides not currently avail‐ able for public health (chlorfenapyr and indoxacarb), potentially effective in areas with pyr‐ ethroid resistance (N'Guessan et al., 2007a; N'Guessan et al., 2007b), and new formulations of existing insecticides with prolonged residual activity (Hemingway et al., 2006).

The main alternative to IRS are ITNs, which have been shown convincingly to substantially reduce all-cause child mortality, under both experimental (Lengeler, 2004) and operational conditions (Schellenberg et al., 2001; Fegan et al., 2007). Various new developments in ITN technology have spread recently. At least one nonpyrethroid insecticide with novel chemis‐ try has been developed for ITNs (Hemingway et al., 2006) to cope with the problem of re‐ sistance; however, safety issues are still a concern. Other new ITN products are not expected to come to market in the short term.

Chemical insecticides as larvicides can play an important role to control mosquito breeding in urban settings, but they are a concern to the integrity of aquatic ecosystems.

Moreover, in order to push away mosquitoes, which usually are attracted by the moisture, warmth, carbon dioxide or estrogens from human skin, a large spectrum of repellents have been developed and are currently used; these substances, manufactured in several forms, in‐ cluding aerosols, creams, lotions, suntan oils, grease sticks and cloth-impregnating laundry emulsions, are usually applied on the skin or clothes, and produce a vapor layer character‐ ized by bad smell or taste to insects (Brown & Hebert, 1997). The ideal repellent should sat‐ isfy several criteria: a) have long-lasting effectiveness; b) do not irritate human skin; c) have a bad odor only to mosquitoes but not to people; d) have no effects on clothes; e) be inert to plastics commonly used, such as glasses or bracelets; f)be chemically stable; and g) be eco‐ nomical (Brown & Hebert, 1997). The list of main insect repellents, some of which are also used as insecticides, includes N,N-diethyl-3-methylbenzamide (DEET), permethrin, picari‐ din, indalone, and botanicals (Prato et al., 2012). Additionally, innovative work is in prog‐ ress on the attractiveness of human odors to malaria vectors, with potential applications as mosquito attractants and repellents for use in trapping and personal protection (Zwiebel & Takken, 2004).

velopment. Several mosquito species vectors of different parasites and viruses have been transformed. Some of the transformed mosquitoes were shown capable of blocking patho‐ gen development via tissue-specific expression of molecules impairing the pathogen attach‐ ment to the midgut (Ito et al., 2002), or activating some biochemical pathways detrimental to pathogen survival (Franz et al., 2006). Paratransgenesis aims to reduce vector competence by genetically manipulating symbionts. Transformed symbionts are spread maternally or via

DDT as Anti-Malaria Tool: The Bull in the China Shop or the Elephant in the Room?

http://dx.doi.org/10.5772/53241

351

Unfortunately, although these approaches are potentially promising, they remain a com‐ plex approach with a limited use (Coutinho-Abreu et al., 2010). Also, data on the cost-ef‐ fectiveness of nonchemical methods are scarce. In a retrospective analysis of data from Zambia, environmental management was as cost-effective as ITNs (Utzinger et al., 2001). Moreover, environmental management can benefit from local resources, reducing the

To date, DDT represents a major tool for vector control in areas endemic for malaria, and in 2010 it was the main stay contributing to reduce malaria burden. Despite the big ongoing debate whether improve or ban its use, no convincing evidence on long-term toxic effects of DDT on humans is currently available. In the future, further constructive research aimed at ascertaining DDT effects on human health will be certainly welcome; also, the concurrent use of safe DDT alternatives (as long as they are effective as DDT, of course), should not be neglected. Nevertheless, DDT benefits appear self-evident up to now, thereby justifying its

and Giuliana Giribaldi1

1 Dipartimento di Genetica, Biologia e Biochimica, Facolta' di Medicina e Chirurgia, Univer‐

2 Dipartimento di Neuroscienze, Facolta' di Medicina e Chirurgia, Universita' di Torino, Italy

[1] Africa Fighting Malaria (2010). Africa Fighting Malaria. Indoor Residual Spraying and DDT. Available from http://www.fightingmalaria.org/pdfs/Africa%20Fighting

coprophagy across an insect population (Durvasula et al., 1997).

need for external funds.

current use as an effective anti-malaria tool.

%20Malaria% 20IRS%20DDT%20issues.pdf

Mauro Prato1,2, Manuela Polimeni1

**9. Conclusion**

**Author details**

sita' di Torino, Italy

**References**

#### **8.2. Nonchemical methods**

The development of non-chemical strategies alternative to insecticides and repellents is al‐ ready available or currently on study. Before the advent of synthetic insecticides, vector con‐ trol depended primarily on environmental management, and a meta-analysis of data mostly from that period indicated that it substantially reduced malaria risk (Keiser et al., 2005).

Elimination of vector-breeding habitats and managements of water bodies plays a key role in vector suppression, (Walker & Lynch, 2007). In irrigated agriculture, vector breeding can be controlled, through land leveling and intermittent irrigation (Keiser et al., 2002).

The role of aquatic predators as control agents of malaria vectors is potentially enhanced through conservation or through the introduction of agents from outside. Larvivorous fish have frequently been reared and released for controlling vector breeding in small water tanks and wells, but successes have generally been limited to more or less permanent water bodies (Walker & Lynch, 2007).

Microbial larvicides such as *Bacillus thuringiensis israelensis* and *Bacillus sphaericus* produce mosquito-specific toxins associated with a low risk of resistance development (Lacey, 2007). Recent field trials and pilot projects have shown good potential of both bacteria to manage mosquito breeding and to reduce biting rates in certain settings (Fillinger et al., 2008).

Also, insect pathogenic fungi have shown promising results for controlling adult *Anopheles* mosquitoes when sprayed on indoor surfaces and have potential to substantially reduce ma‐ laria transmission (Scholte et al., 2005).

Novel methods under development are genetically engineered mosquitoes and the sterile insect technique (Catteruccia, 2007). Genetic control appears a promising tool, comprising all methods by which a mechanism for pest or vector control is introduced into a wild popula‐ tion through mating. These include the sterile insect release method or the sterile insect tech‐ nique (SIT), through which males are sterilized by irradiation or other means and released to mate with wild females, leading them to lay sterile eggs. Additionally, the introduction of genetic factors into wild populations aimed to make pests harmless to humans might be rel‐ evant (Pates & Curtis, 2005).

Finally novel approaches against vector borne diseases include transgenesis and paratrans‐ genesis to reduce vector competence (Coutinho-Abreu et al., 2010). For vector transgenesis, the goal is to transform vectors with a gene (or genes) whose protein(s) impair pathogen de‐ velopment. Several mosquito species vectors of different parasites and viruses have been transformed. Some of the transformed mosquitoes were shown capable of blocking patho‐ gen development via tissue-specific expression of molecules impairing the pathogen attach‐ ment to the midgut (Ito et al., 2002), or activating some biochemical pathways detrimental to pathogen survival (Franz et al., 2006). Paratransgenesis aims to reduce vector competence by genetically manipulating symbionts. Transformed symbionts are spread maternally or via coprophagy across an insect population (Durvasula et al., 1997).

Unfortunately, although these approaches are potentially promising, they remain a com‐ plex approach with a limited use (Coutinho-Abreu et al., 2010). Also, data on the cost-ef‐ fectiveness of nonchemical methods are scarce. In a retrospective analysis of data from Zambia, environmental management was as cost-effective as ITNs (Utzinger et al., 2001). Moreover, environmental management can benefit from local resources, reducing the need for external funds.
