CASE NOTES


RABIES AND LYME DISEASE—CHALLENGES IN DISEASE CONTROL

Matthew Ball- Senior District Veterinarian, Lismore

Posted Flock & Herd March 2011

SUCCESS IN ANIMAL DISEASE CONTROL AND ERADICATION PROGRAMS

The control and eradication of animal diseases should be based on an understanding of their epidemiology and the methods available for their diagnosis, prevention and treatment. For control to be successful there needs to be both adequate funding and recognition by relevant stakeholders that control of the disease is important. Epidemiological, economic and social factors must also be favourable (Animal Health Australia, 2003).

Australia has had considerable experience in disease control and eradication programs. Work on diseases such as bovine tuberculosis, brucellosis, Johne's disease and equine influenza has highlighted that for success there is a need for a clear cost-benefit analysis, effective diagnostic tests, good case definition, a technique to effectively break transmission and, ideally, no adverse effects on natural ecology.

In addition, disease control programs need to have adequate resources, governance, legislative support and an appropriate emphasis on any public health risk of the disease. Disease control is difficult for both developing and developed nations. Attempts to control the recent outbreak of rabies in Bali and Lyme disease in North America are useful case studies for Australian authorities to further appreciate the challenges of animal disease control.

THE INDONESIAN CAMPAIGN AGAINST RABIES

Rabies was first diagnosed in Indonesia in 1884 and became endemic in many provinces, but not in eastern provinces such as Flores and Bali. Dogs are responsible for 98% of disease transmission (Suroso and Simanjuntak 1997). A national control program has been in place since 1926 (Akoso, 2001). In 1989, it was decided to eradicate the disease by the year 2000. This was considered feasible because no wild animal reservoir had been found and the risk of spread by island-island transportation was considered amenable to control.

Eradication programs commenced in Java and Kalimantan in 1993 as a 'Cross-Coordination Program' of both the Health and Agriculture Departments (Suroso and Simanjuntak, 1997). Control strategies were based on those recommended by the World Health Organisation (WHO) and included attempts at mass vaccination of 70% of the dogs and elimination of stray dogs. In very endemic areas, called 'first circle areas', vaccines conferring 3-year immunity were used while in other areas a less expensive but shorter duration vaccine was used. The Health Department ensured that it could provide post exposure treatment (PET) to those bitten and pre-exposure treatment for those at high risk. Surveillance and community participation was also to be implemented (WHO, 1993).

These control strategies ultimately provided freedom from rabies in some areas of Java, reduced the overall number of animal cases of rabies, and reduced both the total number of human patients requiring PET and the number of human deaths (Suroso and Simanjuntak 1997). However, the disease was not eradicated by 2000. Infection re-emerged in West Java after assumed freedom. It also persisted in other endemic areas and spread in 1998 to Flores. The more recent spread to Bali occurred in 2008. The risk that infected animals, especially dogs on fishing or people-smuggling boats, are introduced to northern Australia has now increased (ACIAR, 2010).

The Bali outbreak began following the movement of an infected dog from Flores to the southern peninsular of Bali in July 2008. There was inadequate surveillance to identify the outbreak at that time and the disease was not officially recognised until late 2008 (Clifton, 2010). The Australian Centre has recognized this delay in detecting rabies for International Agricultural Research (ACIAR) as evidence of the need for greater coordination of Indonesian veterinary, quarantine and human health services (ACIAR, 2010). 

The initial disease control program in Bali attempted to restrict the outbreak to the peninsular. Reasons for initial failure in this control program include the high density of free roaming dogs and inadequate control measures. It is estimated that there were between 500,000 and 600,000 dogs in Bali with 150 dogs per square kilometre (FAO, 2009). Balinese usually let their dogs roam free (ABC, 2010). Poor public awareness, limited local diagnostic capacity, fragmented command structures and inappropriate strategies including poor vaccine choices are factors slowing down control (FAO, 2009).

The control program initially exterminated dogs as the primary control method. Some vaccine was also used. Strychnine darts were used for much of the dog control. The dog controls increasingly generated local and international opposition from welfare agencies. Other opposition was based on the recognition that international expertise considers rabies control strategies relying mainly on dog control as being ineffective (Muller, 2009). Ausvetplan (1996) describes how historical outbreaks in the USA were not controlled by very effective dog control but once mass dog vaccination was introduced control was achieved within 12 months. WHO (2010) advises that the most effective control method is mass vaccination of at least 70% of the dog population. No doubt, however, starting dog control was initially easier to implement in Bali than a more complex vaccination strategy.

It is now recognised that the authorities did not vaccinate enough dogs on the peninsular to keep the outbreak confined. FAO (2009) estimated that less than 20% were vaccinated. During the free vaccination campaigns, there was minimal interest by the community with a resultant low turnout. This reluctance to have their dogs vaccinated was probably because of poor knowledge of importance, a misunderstanding that the vaccine could cause the disease or in some cases because dogs were intended for human consumption (FAO, 2009).

The type of animal vaccine used by the Bali administration has also been criticised. Initially imported vaccines were not permitted and vaccination was only allowed in the 'infected area'. The local 'Pusvetma' vaccine used was of unknown quality with duration of only 3 months (FAO, 2009). The more widespread use of a superior 3-year duration vaccine would have created a buffer zone ahead of the disease spread.

By February 2010, it was claimed by Balinese authorities that more than 100,000 dogs had been killed and more than 300,000 dogs vaccinated (Jakarta Post, 2010). Probably just as many dogs remained unvaccinated. The lack of adequate surveillance data makes it difficult to monitor control efforts. Initial and ongoing surveillance has been inadequate (Clifton, 2010). However, by September 2010, rabies is known to have spread to nearly all municipalities in Bali and at least 76 people have died. The number of reported dog bites has continued to increase with 34,000 in the first half of 2010 (Jakarta Post, 2010).

The use of PET is stretching the financial resources of the Indonesian health system with a cost of $AUS350, 000 a month. One suggestion being made to Indonesia is to change from an intramuscular PET to a WHO recommended intradermal PET because this uses 5 times less product (Promed, 2010).

Lack of community support is identified as a reason for poor outbreak control. Community support is needed to ensure enough dogs are vaccinated or removed. Purnama (2010) outlines how more effective control was delivered in Balinese sites where the provincial health and livestock authorities were able to collaborate with the traditional 'pakraman' village leadership. 

To improve community support effective and consistent communication to the community is needed. Improving understanding of the disease, minimising dog bites, responsible dog ownership, animal welfare and promotion of vaccination needs to be covered by public awareness activities. In one example in West Java, a collaborative effort between the Alliance for Rabies Control, Livestock Service Office for Sukabumi and the Centre for Indonesian Veterinary Analytical Studies has worked on developing effective education messages to school children and the wild boar hunting society. This society was chosen as a target audience as there is a low uptake of vaccination of their dogs. Oral presentations, a booklet and a comic book have been developed (Alliance for Rabies Control, 2010). Such work would also be invaluable in Bali.

Interagency collaboration and especially a 'one health' approach by medical and veterinary agencies is recognised as being necessary to deal effectively with zoonotic disease outbreaks. The FAO initial assistance mission in 2009 identified that much greater coordination, communication and cooperation was needed between human and animal health services (FAO, 2009). Better control of rabies in dogs by agricultural agencies is the best way to protect human health. Unfortunately, the disease can be viewed by agricultural services as of lower priority because it does not relate to food production (Suroso and Simanjuntak, 1997).

There still appears to be a lack of a well-organised vaccination strategy in Bali. Such a strategy should be long term and begin by accurately estimating dog density and classification of dogs as to whether they are owned or un-owned. Relative use of parenteral or oral vaccine use should be determined. Ensuring 70% coverage for all dogs, irrelevant of ownership status, is needed in the strategy. Only this will reduce the contact rate between rabid animals and unvaccinated animals to a level too low to sustain rabies transmission.

In September 2010, the Bali administration announced that it hopes to achieve eradication of rabies by 2012. A new campaign, more fitting with international recommendations, has been planned. Attempts will be made to vaccinate all dogs remaining on the island by the end of the year. Two hundred teams with each team comprising dogcatchers and vaccinators will do this mass vaccination drive. An imported, internationally approved, vaccine will be used. This vaccination drive is intended to be followed up again in June 2011. The central government has allocated Rp 15 billion and the Bali administration has allocated Rp 3.3 billion to fund the drive.

The Bali administration also plans to create new laws that will require all dogs to be restrained or risk being impounded and killed (ABC, 2010). It seems unlikely that a high rate of compliance with these laws would be achieved. There is also a suggestion that for a rural village based community such laws would only create animal welfare concerns, as the free roaming nature of dogs is necessary for the dogs' survival.

Despite the optimism associated with these announcements it remains to be seen whether there will be adequate resources and commitment to achieve eradication. It seems likely that without well-designed education campaigns, inter-sectoral cooperation, community participation, adequate resources and local commitment a widespread vaccination campaign will not be effective and rabies will be in Bali for many years to come.

NORTH AMERICAN CAMPAIGN AGAINST LYME DISEASE

Lyme disease in humans was first recognised in Lyme, Connecticut, in 1975. The disease was most likely introduced from Europe in the early 1900's but was not recognised as a distinct illness. Signs of disease in humans include a slowly expanding rash and, if untreated, possible complications from nerve disease, heart disease and arthritis. It is caused by the bacterium Borrelia burgdorferi and is spread by the bite of infected black-legged ticks Ixodes scapularis and Ixodes pacificus. Immature ticks are found on white-footed mice and adult ticks on deer. These animal hosts serve as reservoirs of infection (CDC, 2010).

There is uncertainty as to whether Lyme disease is present in Australia. A number of doctors on the North Coast of NSW report that they have diagnosed the disease but presence of the disease is controversial (Russell, 1998). Studies have not found the bacterium in our local Ixodes ticks. As the debate continues, it is useful to appreciate the control efforts being carried out in the United States of America (USA).

A range of government and non-government agencies has been involved in the surveillance, control and prevention of Lyme disease. Such agencies include the National Centre for Disease Control (CDC), the Department of Health and Human Services, State Departments of Health and Agriculture, National Park Service and research organisations. The disease has a high profile and lobby groups have been able to attract tens of millions of dollars of federal research dollars annually (Nigrovic and Thompson, 2006). Some of that research is summarised here.

In 1982, the CDC began a surveillance program for Lyme disease and in 1991, the disease was made notifiable (CDC 2005). In 20 years, 145,000 cases were reported (Destroy et al, 2007). Endemic areas have been identified throughout north eastern and north central USA. A control program was considered to be of cost benefit when medical costs and loss of work time were considered. It was calculated that a simple case of Lyme disease cost nearly $US200 and a complicated case with neurological signs or arthritis cost over $US60, 000 (CDC, 1999).

Some disease control strategies involve high cost measures to actively reduce disease agent prevalence. For Lyme disease, measures such as reducing host numbers, application of acaricides to the environment and hosts, and vegetation removal are examples of these more complicated high cost measures. Other disease control strategies take a risk-based approach where the community is provided with adequate information and tools to 'protect' itself. For Lyme disease the promotion of protective behaviours and voluntary vaccination are in this category.

Disease control by reduction of mice or deer hosts is discussed in the literature. Mice control is not practical as they are free ranging (Daltroy et al, 2007). Jordan et al (2007) studied Lyme disease incidence rates before and after the removal of white tailed deer within a residential area. There was no apparent decrease in nymph tick numbers and no variation in the Lyme disease incident rate. Moreover, attempting to control Lyme disease by eliminating deer populations inflames conservationists. Deer reduction, although serving other community goals, is unlikely to be a primary disease control method.

Reducing the number of vector ticks should assist in reducing the prevalence of B. burgdorferi. Because Lyme disease is typically associated with bites from nymphal Ixodes recommendations have been made that acaricidal control of this stage of the ticks should be a major component of disease prevention (Falco et al, 1998). The application of 'barrier' chemicals, that are active against nymphal ticks, has been carried out around homes and other places in endemic areas, but this use of an acaricide is only useful in the short term. Schulze et al (2005) showed the use of granular deltamethrin achieved reductions in the short term but by 12 weeks, the tick population had fully recovered. Long-term consequences of repeated environmental acaricides are unknown (Daltroy et al, 2007). The treatments also come at some cost. Gould et al (2008) found that the Connecticut public is unwilling to spend more than $US100 on environmental tick controls.

Self-treatment acaricide systems have been developed for white-footed mice and white tailed deer. Such systems are costly and only effective in the short term (Daltroy et al, 2007). Simple removal of vegetation can reduce tick habitat and numbers but is not always feasible. While it may be practical in urban gardens, it becomes problematic when attempted on a large scale. Ginsberg and Howard (1994) raise valid concerns that the high profile of the disease has encouraged destruction of vital habitats and indiscriminate use of pesticides.

Integrated vector management strategies may be more successful than relying on a single technique. However, Mount et al (1997) found that even if deer reduction, acaricide self-treatment and vegetation reduction are combined tick densities were reduced by less than 50% in 5 years.

The cost and problems with many forms of control make educational campaigns seem appealing as a primary control method. They are relatively low cost, avoid ecological impacts and can have other health benefits. Such campaigns have focused on enabling the disease to be detected and treated promptly and to encourage preventative measures. A large volume of online material relating to the disease is easily available (New York, 2010; CDC, 2010; Department of Health, 2010).

There has been extensive communication with medical staff to assist them in understanding the disease and getting a diagnosis before chronic disease occurs. Diagnosis of Lyme disease can be difficult as there are limitations in laboratory testing but once suspected the disease is easily treated with antibiotics.

Advice to the public is particularly targeted to those who live or work in areas surrounded by tick-infested woods or overgrown brush as these people are at greater risk of disease exposure. Preventative measures promoted include use of insect repellents containing 20% DEET, protective clothing, inspecting one's body for ticks, correct tick removal and awareness of symptoms, such as a rash, which need medical attention.

Other health benefits occurring secondary to advice for Lyme disease include sun protection reducing skin cancers and insect repellents reducing mosquito borne disease. Encouraging body examination for ticks also fits in with other health messages seeking self-examination of moles and breast lumps.

Unfortunately, public education campaigns have not always been effective in reducing the incidence of Lyme disease (Daltroy et al, 2007). Numerous studies have demonstrated that following long-term educational programs knowledge and awareness of Lyme disease in endemic areas is good. However, this does not necessarily translate to a high rate of preventative behaviour as Shadick et al (1997) identified that, while nearly 80% of people did well in a knowledge test, only 40-60% used tick repellents, protective clothing and tick inspections.

Identification and early removal of ticks can substantially reduce the chance of infection. De Vries et al (2002) discuss how tick inspection of children by their parents is inhibited if they do not consider it a 'social norm'. They recommend that future education programs need to 'openly' stimulate awareness of 'peers' who carry out inspections and emphasise the importance of the inspections.

Perhaps other improvements are also needed with educational campaigns being based more on social educational theory and using novel techniques. In one trial in Nantucket the use of an entertainment troupe doing a performance on disease prevention and distributing educational materials was analysed statistically to have been effective (Daltroy et al, 2007).

The development of vaccines is often considered vital for modern disease control. In fact, a vaccine was developed for Lyme disease but it did not achieve good market uptake. This was mainly because despite being approved there was widespread concern about its efficacy and unknown long-term consequences. In 2002, the manufacturer of the vaccine stopped commercial production. Another vaccine may be developed and be more successfully marketed. The problem with any vaccine is that it may reduce preventative behaviours by at risk people who are then prone to other tick borne infections.

By 2009-2010 Lyme disease public lobbying has culminated in the introduction of a Bill to Congress seeking greater expansion of federal efforts to control Lyme disease and to establish a Tick Borne Diseases Advisory Committee. The Bill includes requests for $US20 million to be authorized annually for research and other activities. All this for a non-fatal disease whose cause is known, has an effective treatment and can be prevented if the public was to follow advisory messages.

In developing nations, the control of serious zoonoses, such as rabies, is challenged by lack of resources, public understanding and institutional commitment. In developed wealthy countries, the 'informed' public can have a large influence on resourcing for disease control. Institutional resource allocation may not match either the science or cost benefit analysis but may be politically astute.

Reference list available on request

 


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