Introduction to Vector-Borne Disease Risk

**3**

**Chapter 1**

*David Claborn*

**1. Introduction**

Introductory Chapter:

Vector-Borne Diseases

and yellow fever have been extremely important [2].

cycles are as diverse as the range of vectors.

In the waning years of the nineteenth century, Theobald Smith convincingly proved that Texas cattle fever was caused by a protozoan parasite and, perhaps more importantly, was transmitted to cattle by a tick. This was the first definitive proof of vector-borne transmission by an arthropod [1]. Within a few years, scientists demonstrated transmission of human disease agents by vectors for a variety of diseases, from filariasis to malaria. Since then, vector-borne transmission has proven to be a major means of disease for dozens of diseases, some of great public health importance. **Table 1** provides a partial list of vector-borne diseases along with the disease agents and vectors for each. Malaria is probably the vector-borne disease with the largest impact on human health today, though historically typhus, bubonic plague,

Despite extraordinary efforts to control or eliminate vector-borne diseases, they persist. Estimates of mortality due to malaria alone exceed 400,000 per year [3]. For the millions of survivors of malaria infection, the costs of disease and disability are enormous. And this reflects a recent improvement over previous years. Great effort has gone into reducing the incidence of malaria, reflecting the dedication of governments, nongovernmental organizations, charitable agencies, scientists, and medical workers. Despite significant success with reducing the rates of diseases like malaria, typhus, and yellow fever, vector-borne diseases persist. Of the 20 illnesses listed as neglected tropical diseases by the World Health Organization in 2020, 6 are primarily transmitted by vectors: American trypanosomiasis, African trypanosomiasis, dengue (and chikungunya), leishmaniasis, lymphatic filariasis, and onchocerciasis. Some of the others, like trachoma, may also exhibit a vector-borne element through the mechanical transmission of disease agents by filth flies. The vectors represent a wide spectrum of arthropod species, from the ticks and mites of *Arachnida* to the mosquitoes, true bugs, and lice of *Insecta*. The disease transmission

Although the disease transmission cycles of vector-borne diseases can be very complex, they do provide a unique opportunity for prevention or control. For nonvector-borne diseases, prevention can take a variety of forms including immunizations, sanitation, infection control, chemoprophylaxis, curative medicine, and others. For vector-borne disease, however, there is often the possibility of vector control as a means of interrupting the disease cycle. Some vector-borne diseases, such as yellow fever and Japanese encephalitis, can be effectively prevented by immunization, though maintenance of a cold chain to ensure vaccine viability may be necessary and can be difficult to maintain in remote environments. Other diseases such as malaria can be prevented through prophylactic use of drugs. But for many vector-borne diseases, there are no effective vaccines or chemoprophylactic measures. Also, there is no specific treatment for many of the diseases. For such

## **Chapter 1**
