Understanding the Burden of Agriculturally Significant Vector-Borne and Parasitic Diseases in Kansas

Bovine anaplasmosis, a disease caused by the bacterium A. marginale, was first described in KS in 1926 (Kocan et al., 2010). The disease is now widespread throughout the state (Spare et al., 2020), with 54 of 105 counties in KS reporting positive cases between the years of 2023 and 2024 (KSVDL, 2024). It can cause severe anemia, fever, icterus, lethargy, weight loss, abortions, and death in cattle, resulting in significant economic losses to the beef and dairy industries. Fatalities are most common in cattle over 2 years of age (Aubry and Geale, 2011), and those that survive the acute phase of infection become persistently infected (Kocan et al., 2010). The overall expected cost of anaplasmosis in cattle has been estimated at $660 per head (Railey and Marsh, 2021). The largest costs are related to treatment of infected animals and death loss, so monitoring A. marginale prevalence within a herd or region with a commercially available enzyme-linked immunosorbent assay can help minimize outbreaks and associated economic losses (Railey and Marsh, 2021).

A. marginale can be transmitted by ticks, biting flies, and fomites contaminated with infected blood. Approximately 20 species of ticks are thought to be capable vectors of A. marginale globally (Kocan et al., 2004), but the tick vector of most concern in KS is Dermacentor variabilis, also known as the American dog tick. It is one of the most common tick species in KS, with peak activity occurring in spring and summer (Hroobi et al., 2021, Ng’eno et al., 2024). Male Dermacentor ticks are known to become persistently infected with A. marginale, making them capable of repeatedly transmitting the disease agent when they transfer between cattle (Kocan et al., 2010). In addition to bovine anaplasmosis, D. variabilis also transmits the bacteria that cause tularemia and Rocky Mountain spotted fever. An increase in abundance of D. variabilis and shifts in its range possibly due to climate change may partially explain why these diseases have increased in incidence (Boorgula et al., 2020). Several studies have demonstrated that prescribed burning of pastures may offer an affordable, chemical-free method of decreasing tick burden on cattle (Gleim et al., 2019; Salazar et al., 2024; Victoria et al., 2013).

T. orientalis is a tick-vectored protozoan parasite capable of infecting red and white blood cells in cattle, resulting in infectious anemia. There are 11 genotypes of T. orientalis, but most do not cause clinical disease. The Ikeda and Chitose genotypes are pathogenic, causing anemia, abortion, fever, weakness, and death in infected cattle (Gebrekidan et al., 2020). Unlike A. marginale, T. orientalis is known to cause disease in calves under 2 years of age. After recovery, animals remain persistently infected reservoirs, and symptoms can reoccur in times of stress (Hanzlicek, 2022). To date, theileriosis outbreaks have been reported in 15 states in the United States, including KS (APHIS, 2024). The economic burden of bovine theileriosis in beef cattle involves losses due to quarantine, decreased production, and euthanasia of infected animals (Almazán et al., 2022), but overall estimates of economic losses in the United States are lacking.

H. longicornis, the Asian longhorned tick, is the primary tick vector of T. orientalis (Dinkel et al., 2021). It is an exotic tick species that was first detected in the United States in 2017 and has since been reported in 19 states (Ponnusamy et al., 2024). The spread of H. longicornis in the United States is facilitated over long distances by companion animal transport and over shorter distances by roaming wildlife (Egizi et al., 2020). Based on the latest data released by the USDA in February of 2023, H. longicornis was detected in Missouri, 50 miles east of the border with KS (APHIS, 2023). This species was also found on cattle in Craig County, Oklahoma, which borders KS to the south, in July of 2024 (Myers and Scimeca, 2024). It is an aggressive biter with a broad host range (humans, domestic animals, and wildlife), building intense infestations upon domestic hosts and causing great stress, reduced growth, and severe blood loss. Females can reproduce parthenogenetically, enabling the establishment of new populations through the introduction of a single female (Herrin and Oliver, 1974). A recent model predicts the spread of H. longicornis within the United States, with highly suitable habitat existing on the east and west coast and in several midwestern and southern states (Rochlin, 2019). If H. longicornis spreads into KS, it is feasible that cases of bovine theileriosis will become more common, threatening the state’s cattle industry. Currently, the dominant control strategy is the use of acaricides to control tick vector populations, but it is financially costly and the widespread use of these chemicals has resulted in increased tick resistance. Selectively breeding cattle that are genetically resistant to the disease may be a cost-effective alternative with promise for the future (Valente et al., 2022).

ASFV is a large DNA virus and the only member of the family Asfarviridae and genus Asfivirus. ASFV is also unique because it is the only known DNA arbovirus. It infects wild and domestic swine, including African warthogs and giant forest hogs, which normally have inapparent infections, and European wild boars, which often show clinical signs. Clinical signs in domestic swine infected with highly virulent ASFV can be peracute with sudden death and a mortality rate near 100% after 6–20 days. Clinical signs with less virulent ASFV can be subacute or chronic (Fernández and White, 2016). This virus has been introduced, eradicated, and reintroduced into various countries in Europe and the Caribbean and, over the past 10 years, has been introduced into the Caucasus, Russia, and Asia. It is not currently found in the United States but is of concern as a potential introduction due to its recent expansion within Europe, Asia, Haiti, and the Dominican Republic (Brown and Bevins, 2018; Cochran et al., 2023; Ruiz-Saenz et al., 2022).

ASFV is highly stable in feed and soil and is transmitted through direct contact with infected pigs or fomites, consumption of contaminated food products, and tick bites (Cochran et al., 2023). Tick vectors include several species within the Ornithodoros genus (Hess et al., 1987). At least one of those species, Ornithodoros turicata, is present in KS. These ticks feed indiscriminately on numerous host species, including cattle and pigs, but can survive for years without feeding. They are long-lived and have highly adaptable feeding behaviors, which makes them excellent vectors (Donaldson et al., 2016). Considering KS is home to a known vector and host species of domestic and feral swine, it is possible that ASFV could become established in KS if it were to be introduced into the United States. The economic burden of such an outbreak would be significant considering there is no commercially available vaccine for ASFV in the United States and control relies heavily on culling all pigs within specified control zones (Cochran et al., 2023). In 2021, a publication from Iowa State University estimated the cost, were ASFV to enter the United States, would be anywhere from $15 billion to $50 billion (Carriquiry et al., 2021).

CVV is a mosquito-borne orthobunyavirus that was first isolated from a Culiseta inornata mosquito in 1956 in Cache Valley, Utah, USA (Holden and Hess, 1959). The virus is now endemic in North America and has been isolated from at least 30 species of mosquitoes, but the primary vector species are unknown (Ayers et al., 2019). Infected mosquitoes can transmit the virus to cattle, sheep, goats, deer, and humans (Uehlinger et al., 2018). Based on serological studies, white-tailed deer are thought to be the main amplifying host (Blackmore and Grimstad, 1998; Muller et al., 2024). However, CVV is primarily a concern in pregnant ewes, because it causes embryonic death, abortion, and fetal malformations (Ayers et al., 2023; Edwards et al., 1989). In rare circumstances, CVV has also caused severe disease in humans even though humans are not part of the virus cycle and are considered incidental hosts (Ayers et al., 2023; Campbell et al., 2006; Wilson et al., 2017).

KS is home to Anopheles punctipennis and Anopheles quadrimaculatus (Garrison, 2018), which are both competent mosquito vectors of CVV (Andreadis et al., 2014). Aedes spp. found in KS are also competent vectors (Ayers et al., 2019). Cases of CVV in small ruminants are reported sporadically in KS, with positive cases being confirmed by the KS State Veterinary Diagnostic Laboratory as recently as 2020 (Cino, 2020). A 2011 study reported a 28% seroprevalence in sheep across 22 states, providing evidence that CVV infections are common throughout the United States (Meyers et al., 2015). There are currently no approved vaccines available for CVV (Ayers et al., 2023), although experimental vaccines have been evaluated and shown to induce an adequate neutralizing antibody response (Ayers et al., 2022; Dunlop et al., 2018). Due to inconsistency in the timing of outbreaks and the lack of longitudinal data in the United States, there are still considerable gaps in knowledge regarding appropriate control measures and the economic burden of CVV (Hughes et al., 2023).

RVFV is a mosquito-borne phlebovirus that affects humans and livestock (Wang et al., 2022). It was first identified in Kenya in 1930 (Daubney et al., 1931), and is now endemic in the eastern and southern regions of Africa (Favier et al., 2006). It has caused major outbreaks in at least 11 countries in Africa and the Arabian Peninsula (Bird et al., 2009) and has spread geographically due to climate change, making it a hazard to nonepidemic countries (Bett et al., 2017; Fouque and Reeder, 2019; Iwamura et al., 2020; Kamal et al., 2018; Samy et al., 2016). Economically, sheep, goats, and cattle are the most important domestic animal hosts (Favier et al., 2006). RVFV-infected pregnant goats, sheep, and cattle experience high rates of spontaneous abortions and high fatality rates in young animals (Coetzer, 1982; Ikegami and Makino, 2011). Experimentally, RVFV can infect white-tailed deer, so the virus has the potential to also become established in wildlife if introduced to the United States (Gaudreault et al., 2015; Kakani et al., 2010; Wilson et al., 2018). The possible impacts of RVFV on North American agriculture and public health are considerable (Bird et al., 2009; Hartley et al., 2011; Pendell et al., 2016). Economic impacts on the agricultural industry could result from decreased production, culling of infected animals, decline in consumer demand for meat and dairy products, and international trade restrictions (Hartley et al., 2011; Pendell et al., 2016). In 2016, a model was created that predicted the entry of RVFV into KS via just 10 mosquitoes could cost the United States roughly $3.5 billion (Pendell et al., 2016). Due to its potential to be used as a bioweapon and absence of FDA-approved antiviral therapies or licensed vaccines for humans, RVFV is listed as a select agent by the Centers for Disease Control and Prevention and U.S. Department of Agriculture and classified as a Category A pathogen by the National Institutes of Health (Ayers et al., 2023a).

RVFV can be transmitted by numerous species of mosquitoes in several genera, including several species within the Aedes genus (Linthicum et al., 2016). KS is home to several Aedes species, including Ae. vexans, Ae. albopictus, and Ae. aegypti (Garrison, 2018), which have all been shown to be competent vectors for RVFV in a laboratory setting (Hoch et al., 1985; Turell et al., 1988; Turell et al., 2013). Aedes mosquitoes are floodwater species, which lay their eggs just above the waterline in aquatic habitats. Their eggs remain dormant during periods of drought and hatch when subsequently flooded with water. Field observations suggest that Aedes spp. are able to vertically transmit RVFV via transovarial transmission. The infected eggs remain dormant during dry spells only to hatch after a heavy rain (Linthicum et al., 1985). Therefore, Aedes spp. could play a key role in the maintenance of RVFV during winter and interepidemic periods if it were introduced into KS. In addition to Aedes spp., other mosquitoes in the Culex and Anopheles genus have been documented as important in the amplification of RVFV during outbreaks (Himeidan et al., 2014). In KS, Culex tarsalis may play a role as an important vector (Gorris et al., 2021; Turell et al., 2010). Other than mosquitoes, the virus infection is acquired through exposure to infectious aerosols, handling of aborted fetal tissue, or during slaughtering or necropsy of viremic animals (Meegan, 1981; Meegan et al., 1981; Van Velden et al., 1977). Control strategies for RVFV in the United States would likely involve the widespread use of insecticides targeting adult female mosquitoes alone or in combination with those that target mosquito larvae (Hartley et al., 2011).

JEV is a mosquito-borne flavivirus endemic to the Asia-Pacific region. Mosquitoes transmit the virus to Ardeid birds (herons, egrets, and bitterns), which act mostly as maintenance hosts, and pigs, which act as amplifying hosts. Humans and horses are dead-end hosts (Mackenzie et al., 2022). JEV is of significant agricultural concern to the United States, because it causes reproductive disease in pigs leading to abortions and stillbirths (Oliveira et al., 2019). The introduction of JEV into Australia in 2021 and its subsequent establishment (Williams et al., 2022) is evidence of the virus’s capacity to spread into new areas where all components of the transmission cycle are present, including susceptible mosquitoes (Huang et al., 2015; VDH, 2025) and susceptible domestic and feral phenotype pigs (Lyons et al., 2018; Park et al., 2018b). If introduced into the United States, the mechanisms by which the virus could survive the winter are unknown but could include transovarial transmission (Dixon et al., 2024; Mourya et al., 1991; Rosen et al., 1980; Rosen et al., 1978; Soman and Mourya, 1985). Economic losses associated with such an introduction have been predicted to total between $306 and $612 million in a 1-year outbreak scenario (Cook et al., 2024).

Susceptible species of mosquitoes, birds, and swine are present in KS. Susceptible species of mosquitoes in KS include Culex pipiens and Culex quinquefasciatus (Gorris et al., 2021). Both species have been shown to be competent vectors for JEV (Auerswald et al., 2021). While there is an approved vaccine for humans, there are currently no approved veterinary vaccines for JEV in the United States. Therefore, until a vaccine could be approved, control mechanisms would likely involve attempting to control mosquito populations around pig production facilities and limiting the movement of pigs (Monath, 2023). Culex mosquitoes are also known vectors of several other disease-causing viruses within and outside of the United States, including eastern equine encephalitis virus, western equine encephalitis virus, Venezuelan equine encephalitis virus, Zika virus, St. Louis encephalitis virus, and WNV (Gorris et al., 2021). Changes to average temperatures and precipitation due to climate change will likely cause shifts in Culex spp. distributions in the coming years, opening up opportunities for these diseases to shift into new geographic areas (Gorris et al., 2021). Since WNV and JEV are closely related and share the same vectors, if JEV were to be introduced here it could likely become established just as WNV has been. However, differences in the transmission cycle, notably the importance of swine as an amplifying host for JEV but not WNV, mean that extrapolation of distribution and incidences must be made with caution.